Treatment for Adolescent Marijuana Abuse: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Treatment for Adolescent Marijuana Abuse (NCT00580671), a randomized na study. The primary outcome is Marijuana Abstinence (2 Weeks or Greater).

2. Clinical Question

The trial’s stated aim was to develop and test behavioral treatments intended to enhance treatment outcomes and to learn about mechanisms of change. The registry summary describes prior work motivating a contingency-management approach, but the results concern this randomized study. They describe observed group rates and unadjusted comparisons; they do not, on their own, establish why any group differences occurred.

Further details about eligibility, recruitment, setting, baseline characteristics, and the intended primary statistical model are not reported in the registry record. Those omissions limit assessment of how closely the enrolled participants represent a broader adolescent treatment population and how the reported comparisons relate to any prespecified analysis.

3. Trial Design

This was a completed, randomized, parallel-group behavioral trial with no masking reported. The registry lists a total enrollment of 153 and three arms of 51 participants each. The study began in 2007-11, and primary completion was in 2012-07. The registry identifies Dartmouth-Hitchcock Medical Center as the sponsor.

All three arms received integrated psychosocial counseling described as motivational enhancement therapy and cognitive behavioral therapy. The counseling schedule was 14 weekly sessions. One arm added contingency management, with twice-weekly urine testing and abstinence-based incentives tied to test results. A third arm combined contingency management with 14 weekly behavioral parenting sessions. The design therefore permits comparisons between counseling alone and added behavioral components, as well as between the two arms that included contingency management.

The primary outcome concerns verified abstinence during treatment, not abstinence over a follow-up period. The registry identifies a secondary outcome measuring the proportion of days abstinent across the 14-week treatment period, based on self-report collected twice weekly. Details of any later follow-up outcome are not part of the posted outcome results.

Although allocation was randomized, the method used to generate the allocation sequence, conceal allocation, handle deviations from assigned treatment, and define the analysis population is not reported in the registry record. The original sample-size justification, trial-specific power assumptions, and planned statistical methods are also not reported in the registry record. Accordingly, the summaries support descriptive comparisons among the three randomized groups, but do not reveal every design or analysis decision that would be needed to evaluate the original protocol in full.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: Clients were enrolled into the study and assessed for eligibility, if eligible they were given the choice to proceed. Reasons for ineligibility included no marijuana (MJ) use in past 30 days, failure to meet MJ abuse/dependence criteria, met dependence for another substance, no parent participant, plans to move away, low IQ

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Marijuana Abstinence (2 Weeks or Greater), measured over Testing done twice weekly for 14 weeks..

The primary endpoint is the percentage of participants who achieved at least 2 continuous weeks of marijuana abstinence during the 14 weeks of treatment. Abstinence was verified by urine tests conducted twice weekly. The endpoint is binary at the participant level: each participant either met the stated continuous-abstinence criterion or did not.

A continuous interval of verified abstinence captures a sustained treatment-period outcome rather than a single test result. Repeated urine testing provides an objective verification method for the outcome as defined in the registry. The resulting percentage is straightforward to interpret as the share of participants in each arm who reached the endpoint. It does not describe how many total abstinent days each participant had, nor does it measure abstinence after treatment ended.

The posted results report 72.5% for the arm receiving counseling, contingency management, and behavioral parenting treatment; 68.6% for counseling plus contingency management; and 45.1% for counseling alone. The corresponding endpoint counts are 37 of 51, 35 of 51, and 23 of 51 participants. These rates are the observed group summaries. They do not convey by themselves the uncertainty in the comparisons or establish that treatment assignment caused the observed differences.

The outcome is specific to the registry’s definition and measurement schedule. Missing urine tests, rules for classifying incomplete testing, and the handling of participants who did not complete treatment are not reported in the registry record. Such rules can affect how a binary abstinence endpoint is interpreted, so the posted percentages should be read alongside that limitation.

7. Results Posted in the Registry

• MET/CBT+CM: 68.6% (35/51) versus 72.5% (37/51) on control; risk difference -3.9 percentage points (95% CI -21.6 to 13.7), risk ratio 0.95 (0.74–1.22); unadjusted two-proportion z-test p = 0.664.
• MET/CBT: 45.1% (23/51) versus 72.5% (37/51) on control; risk difference -27.5 percentage points (95% CI -45.8 to -9.1), risk ratio 0.62 (0.44–0.88); unadjusted two-proportion z-test p = 0.005.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Proportion of Days of Marijuana Abstinence Across All Days of Treatment (14 Weeks)

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • MET/CBT+CM: mean 0.82 versus 0.81 on control; difference 0.01 (95% CI -0.11 to 0.13), standardized effect d = 0.04; z-test p = 0.864.
  • MET/CBT: mean 0.79 versus 0.81 on control; difference -0.01 (95% CI -0.13 to 0.10), standardized effect d = -0.05; z-test p = 0.803.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between MET/CBT+CM and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between MET/CBT and the control. The interval gives the range of effects that remain compatible with the data.

The posted secondary outcome summarizes the proportion of days abstinent across the full 14-week treatment period, rather than whether a participant achieved a single continuous interval of abstinence. In broad terms, the group means are similar across the three arms. The unadjusted recalculated comparisons also have intervals that include no difference. This pattern does not mirror a clear separation between the counseling-only arm and the combined contingency-management-and-parenting arm on the primary binary endpoint.

The two measures capture different aspects of behavior. A participant can have a substantial proportion of abstinent days without meeting the primary requirement for 2 continuous weeks, while another participant can meet the continuous-abstinence criterion without having the same overall proportion of abstinent days. Differences between the endpoints are therefore not inherently inconsistent. The secondary measure is based on self-report collected twice weekly, whereas the primary measure uses twice-weekly urine testing to verify the continuous-abstinence criterion.

The secondary comparisons are unadjusted recalculations, and the registry reports no trial analyses for the outcomes. There are three outcome measures listed and a single secondary outcome posted, but a full testing strategy is not reported in the registry record. When multiple outcomes or contrasts are examined, the chance of at least one apparently notable result can increase. Adjustments or prespecified prioritization can address that concern, but neither is documented in the registry record.

For those reasons, the secondary results are best treated as complementary descriptive evidence rather than as an independent confirmation or refutation of the primary comparison. They add information about the distribution of abstinent days over treatment, but they do not settle the interpretation of the verified continuous-abstinence endpoint. Missing-data handling and the analysis population for this measure are also not reported in the registry record.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Proportion of Days of Marijuana Abstinence Across All Days of Treatment (14 Weeks)

9. Statistical Interpretation

10. Statistical Methods Explained

For a binary endpoint such as achieving the stated abstinence criterion, the most direct summary is the proportion meeting the criterion in each group. The registry reports percentages and participant counts. Those summaries preserve the clinical meaning of the endpoint: the percentage of participants whose test results met the continuous-abstinence definition during treatment.

What a risk difference describes

A risk difference is the difference between two group proportions, expressed on the probability scale. A value of zero corresponds to equal observed proportions. The comparisons use the combined counseling, contingency-management, and parenting arm as the reference group. The reported negative estimates mean that the other arm’s observed proportion was lower than the reference arm’s proportion. This direction describes the arithmetic contrast, not a judgment about clinical importance.

The risk difference is useful because it expresses the comparison in percentage-point terms and can be related directly to the observed group rates. It is not the same as a risk ratio or odds ratio. Risk ratios compare proportions multiplicatively, while odds ratios compare odds. Those measures can give a different numerical impression, particularly when an outcome is not rare. The registry also lists recalculated risk-ratio and odds-ratio intervals, but the risk-difference comparisons provide the main interpretation.

Intervals and hypothesis tests

A confidence interval represents a range of values compatible with the observed data under the assumptions of the calculation. Wider intervals indicate less precision. For a difference in proportions, an interval that includes zero is compatible with no group difference as well as with differences in either direction. An interval that excludes zero indicates that the observed contrast is less compatible with equality under the calculation’s assumptions. This is not a guarantee that the contrast is important or that it will recur in another study.

A p value describes how unusual the observed data, or more extreme data, would be under a specified null hypothesis and statistical model. It is not the probability that the null hypothesis is true, and it is not a measure of the size or practical importance of a difference. The comparisons displayed in the registry are unadjusted recalculations from summary counts, rather than reported trial analyses. They should therefore be read as descriptive inferential calculations, not as confirmation of an analysis plan that is not reported in the registry record.

Why the analysis plan matters

Randomization supports comparisons between assigned groups by reducing systematic differences at the point of assignment, on average. It does not remove the need to document the allocation process, analysis population, outcome rules, missing-data approach, and model. Those details determine how the trial’s results should be estimated and how uncertainty should be assessed. They are not reported in the registry record. In particular, without the missing-data rules, readers cannot tell how unavailable or incomplete urine tests contributed to the endpoint classifications.

The registry lists three outcome measures and one posted secondary outcome. It reports no trial analyses in its outcomes record. This means the displayed p values should not be treated as evidence that the trial’s own planned inferential procedure has been reproduced. The protocol’s primary analysis and any adjustment for multiple comparisons are not reported in the registry record.

How to read the continuous secondary outcome

The secondary outcome is the proportion of marijuana-abstinent days across the 14-week treatment period, measured using self-report collected twice weekly. Unlike the primary binary endpoint, this is a continuous summary: it can distinguish participants with different proportions of abstinent days even if they do not meet the primary continuous-abstinence criterion. The registry reports group means and standard deviations, and recalculated mean differences between arms.

A mean difference is the average value in one group minus the average value in the reference group. A difference near zero indicates similar observed averages; its interval conveys the precision of that comparison. A standard deviation describes variability among participant values, not uncertainty in the group mean. The listed secondary comparisons are unadjusted and no trial-reported analyses are present, so they should be interpreted cautiously, especially alongside the number of outcomes considered and the absence of a reported multiplicity plan.

General statistical considerations

General: statistical significance and estimation are related but distinct. A p value evaluates compatibility with a null model, while an interval gives a range of plausible effect sizes under stated assumptions. Both depend on the data and method; neither removes limitations in outcome measurement or missingness. General: over-dispersion matters when the observed variability exceeds what a chosen statistical model expects, because a model that understates variability can make intervals too narrow and tests too liberal. The registry does not report an over-dispersion assessment or a model-based analysis for these outcomes, so this is a general consideration rather than a claim about the trial’s calculations.

11. Confidence Intervals and Precision

Precision varies across the primary comparisons. Each primary arm had 51 participants, so the estimates are based on modest group sizes. The comparison of counseling plus contingency management with the arm also receiving parenting treatment has an interval that spans zero and allows differences in either direction. Its p value is 0.664. The observed rates are close, but the interval does not establish that the groups are equivalent; it leaves uncertainty about the size and direction of the underlying difference.

The comparison between counseling alone and the combined contingency-management-and-parenting arm has an interval that excludes zero, with an unadjusted recalculated p value of 0.005. This indicates greater separation in the observed results than in the other primary comparison, while still leaving uncertainty about the precise magnitude. The interval should be read as a range of effect sizes compatible with the data and calculation, not as a range guaranteed to contain the true effect.

For the secondary proportion-of-days outcome, the registry reports group means and standard deviations, and the recalculated mean-difference intervals include zero for both comparisons. Those results are compatible with little difference in average abstinent-day proportions, but they do not prove equivalence. The registry record does not report a trial analysis or a prespecified equivalence margin.

Confidence intervals and p values come from unadjusted recalculations using the posted summaries. The confidence level and the original trial’s inferential procedures are not reported in the registry record. Precision also cannot be fully assessed without information about missing observations, the analysis population, and the approach to incomplete testing. The participant counts make the denominator clear, but they do not resolve those sources of uncertainty.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are expressed as participants per arm, not as total enrollment or total events. They are illustrations based on the observed effect for each comparison, using a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each planning row considers detecting the stated fraction of the observed effect. The original trial’s sample-size assumptions and justification are not reported in the registry record.

The 80% power column gives the number of participants per arm that the planning calculation would require to have an 80% chance of detecting the specified effect under its assumptions, if that effect were the true one. The 90% power column gives the corresponding planning number for a 90% chance. These are design calculations, not observed characteristics of the completed trial. They do not measure whether the trial actually had a particular probability of finding a result after the data were collected; this is not observed power.

Planning for a smaller fraction of the observed effect requires more participants, because smaller differences are harder to distinguish from random variation. The figures can be very large when the observed effect used for planning is small, as in some comparisons. They should not be interpreted as the trial’s original enrollment target or as a recommendation for a future trial without independent design assumptions. The figures are for two-arm comparisons and do not automatically represent the enrollment needed for a single study comparing all three arms simultaneously.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.725; treatment proportion p₁ = 0.686; average p̄ = 0.706.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6444 = 1.2630.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.6438 = 0.5418.
4. n = (1.2630 + 0.5418)² / (-0.0392)² = 2,118.0, rounded up to 2,119 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.725490196078431                          # control proportion
p1 <- 0.686274509803922                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(580671)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 2,119 (80% power), 2,835 (90% power)
 75% of observed effect: n per arm = 3,730 (80% power), 4,992 (90% power)
 50% of observed effect: n per arm = 8,307 (80% power), 11,121 (90% power)
power.prop.test: 2118 
Simulated power at n = 2,119 per arm: 0.800 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists three outcome measures, including the primary continuous-abstinence endpoint and a posted secondary measure of the proportion of abstinent days. It reports zero analyses in the outcomes record and no trial-reported statistical analyses for the outcomes described. The comparisons discussed are unadjusted recalculations from summary statistics. The protocol’s hierarchy of outcomes, planned contrasts, significance threshold for the primary analysis, and any multiplicity adjustment are not reported in the registry record.

Multiplicity matters when several outcomes or pairwise comparisons are considered. Without a prespecified strategy, an unadjusted p value does not account for the fact that multiple opportunities to observe an unusual result may have been examined. This does not invalidate the descriptive group rates, but it affects how confidently a p value should be treated as confirmatory. The results are accordingly interpreted as unadjusted comparisons rather than as a complete account of a planned testing strategy.

Missing-data methods are also not reported in the registry record. The primary outcome depends on repeated urine testing, but the rules for missed tests, incomplete testing, withdrawal, and endpoint classification are not available. The secondary measure depends on self-report collected twice weekly, and its missing-data rules are likewise not reported. Without these details, readers cannot determine whether all randomized participants contributed to each analysis, whether missing outcomes were imputed, or whether participants with incomplete records were excluded.

The registry reports 51 participants per arm for the primary outcome and different denominators for the secondary means. The reasons for those denominator differences are not reported in the registry record. The analysis population, participant flow, protocol deviations, and use of an intention-to-treat approach are also not reported. These gaps limit evaluation of potential bias due to missing outcomes or exclusions and make it difficult to reproduce the trial’s intended analysis.

15. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 1.96% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: hospitatlization or residential treatment for mental health (11.8%), boot camp, detention, incarceration (11.8%), residential treatment for substance use (7.8%), overdose (2.0%).

For serious adverse events, the registry lists 15 affected participants among 51 at risk in the arm with counseling, contingency management, and parenting treatment; 8 among 51 in the counseling-plus-contingency-management arm; and 6 among 51 in the counseling-only arm. For other adverse events, the corresponding figures are 7, 8, and 4 participants among 51 at risk in each arm. These are counts of participants reported as affected, not a measure of event severity beyond the registry’s serious-versus-other classification.

The registry’s most frequently listed serious-event terms include hospitalization or residential treatment for mental health and boot camp, detention, or incarceration, each reported as 11.8%; residential treatment for substance use, reported as 7.8%; and overdose, reported as 2.0%. The record does not explain whether terms can overlap or whether the listed terms account for all serious events. Death counts are not reported in the registry record.

These figures describe adverse-event reporting within the trial record. They do not establish that an event was caused by an assigned treatment, and the available summary does not provide enough detail to compare event timing, duration, or severity beyond the listed classification. The safety data should be interpreted in the context of the limited reporting detail.

16. What the Result Does, and Does Not, Mean

The posted results show different observed primary abstinence rates across the randomized arms during the 14-week treatment period. The counseling-only arm had a lower observed rate than the arm combining counseling, contingency management, and behavioral parenting treatment. That unadjusted recalculated comparison has an interval that excludes no difference and p = 0.005. By contrast, the observed rate in the counseling-plus-contingency-management arm was close to the rate in the arm that also included parenting treatment; that comparison has p = 0.664 and an interval spanning no difference.

These results do not show which component produced the pattern. Comparing the combined arm with counseling alone changes both contingency management and parenting treatment. Comparing the two arms that include contingency management does not provide a clear distinction in the posted primary outcome, but it also does not establish that the approaches are equivalent. The separate comparison of counseling plus contingency management with counseling alone is uncertain in the registry’s unadjusted results.

The results do not establish that the same differences would occur in other adolescents, treatment settings, or treatment schedules. The registry record does not report detailed eligibility criteria, participant characteristics, trial analysis plans, missing-data rules, or follow-up outcomes sufficient to answer those broader questions. The primary endpoint describes verified abstinence during treatment; it does not establish what happened after treatment ended.

Statistical evidence should not be translated into a claim about an individual participant or a treatment decision. A p value is not the probability that a treatment will produce an outcome, and an interval does not guarantee a future result. The findings are best read as group-level estimates from one randomized trial, with the precision and reporting limitations. No conclusion about clinical care follows from these registry summaries alone.

17. Why This Trial Matters Statistically

This trial is statistically useful because its three-arm structure distinguishes counseling alone, counseling with contingency management, and counseling with both contingency management and behavioral parenting treatment. That arrangement raises a component-attribution question: a difference between the combined arm and counseling alone cannot identify which added component accounts for the contrast. The comparison between the two contingency-management arms helps address the additional parenting component, although its primary outcome estimate is imprecise.

The primary endpoint also illustrates why the outcome definition matters. A binary criterion for at least 2 continuous weeks of verified abstinence answers a different question from the proportion of abstinent days across the treatment period. The two outcomes need not show identical patterns because they summarize different features of participant behavior and use different measurement approaches.

The results demonstrate the distinction between an observed group difference and a precisely estimated contrast. The comparisons have different levels of uncertainty, despite each primary arm having 51 participants. The planning illustrations likewise show that required enrollment depends strongly on the effect size one aims to detect; observed effects that are small yield large planning requirements. Those calculations are not a substitute for a prospective design justification.

Finally, the record underscores the value of reporting analysis plans, missing-data procedures, outcome hierarchies, and participant flow alongside outcome summaries. Without those details, readers can interpret the reported rates and recalculations, but cannot determine how closely they correspond to the trial’s intended confirmatory analysis. The trial therefore offers informative observed comparisons while leaving important statistical design and analysis questions unresolved in the registry record.

18. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.
• Participant counts were reconstructed from posted percentages and arm sizes, so small rounding differences are possible.

Several trial-specific limitations affect interpretation. The total enrollment was 153, with 51 participants in each arm. The primary comparisons therefore rely on a limited number of outcome observations, and at least one interval is broad enough to include no difference and differences in either direction. A lack of clear separation in an unadjusted comparison should not be read as proof that the interventions are identical.

The primary outcome is restricted to verified abstinence during the 14-week treatment period. The registry does not report the detailed rules for missed urine tests or incomplete testing, and it does not provide post-treatment outcome results in the posted outcomes. The secondary measure uses self-report, so it is based on a different measurement source from the primary endpoint. The record does not explain missingness or denominator changes for the secondary outcome.

The trial is unmasked, as reported in the registry. Masking may be difficult to apply to behavioral treatment, but awareness of assigned treatment can matter for expectations, behavior, and self-reported outcomes. The record does not report assessor masking or other procedures that might limit measurement influence.

Other important details are not reported in the registry record: eligibility criteria, baseline characteristics, allocation-sequence methods, concealment, treatment adherence, the original sample-size justification, the planned statistical analysis, multiplicity procedures, analysis populations, and handling of protocol deviations. The posted comparisons are unadjusted recalculations rather than analyses reported by the trial. These limitations do not erase the observed group rates, but they restrict causal interpretation, reproducibility, and generalization.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Treatment for Adolescent Marijuana Abuse — NCT00580671.
• Registry record last updated 2015-08-20; status last verified 2015-07.
• Results first posted 2013-06-05.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

22. Record Summary

The registry record describes NCT00580671, Treatment for Adolescent Marijuana Abuse, a completed randomized, unmasked, parallel-group behavioral trial sponsored by Dartmouth-Hitchcock Medical Center. Enrollment was 153, with three arms of 51 participants each. Each arm received integrated motivational enhancement and cognitive behavioral therapy; two arms added contingency management, and one of those also added behavioral parenting treatment.

The primary outcome was the percentage achieving at least 2 continuous weeks of marijuana abstinence verified by twice-weekly urine testing during 14 weeks of treatment. The posted rates were 72.5%, 68.6%, and 45.1% across the three arms. The registry also posts a secondary measure of the proportion of abstinent days over treatment. Trial-reported analyses, the original sample-size justification, missing-data procedures, and multiplicity methods are not reported in the registry record. The group summaries and unadjusted recalculations should be interpreted with those omissions in mind.