This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Doxazosin for Psychostimulant Dependence (NCT01371851), a randomized phase 1, phase 2 study. The primary outcome is Change in Psychostimulant-positive Urines Over Time.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01371851 |
| Phase | Phase 1, Phase 2 |
| Condition | Methamphetamine or Cocaine Dependence |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Triple |
| Enrollment | 22 |
| Arms in the primary outcome | n/a |
| Lead sponsor | University of Arkansas |
| Results posted | Yes |
2. Clinical Question
Population
Eligible participants with methamphetamine or cocaine dependence who received at least one dose of study medication were included in the stated primary-outcome population. The registry record gives an enrollment of 22, but does not report further eligibility details or the characteristics of participants in the outcome analysis.
Intervention
Doxazosin extended release was started at 4 mg/day. The planned dose increased to 8 mg/day on day 8, with participants maintained on the study until its end.
Comparator
The comparison group received placebo, described as cellulose, throughout the trial. The registry record describes randomized allocation and a parallel-group model.
Primary question
The primary outcome concerns change over time in the proportion of urine samples positive for methamphetamine or cocaine. The registry record does not report numerical outcome results or a single treatment-effect estimate, so the magnitude and precision of any difference between groups are not reported in the registry record.
The study was intended to assess whether doxazosin would reduce stimulant use relative to placebo among participants with psychostimulant dependence. The endpoint relies on urine drug screens collected twice weekly during the 8-week trial, rather than on a self-reported measure alone. The registry description says weekly urine results were averaged within participants and group means were calculated for graphic representation.
The clinical question is narrower than whether doxazosin changes all aspects of dependence or recovery. It asks about a repeated urine-based measure of stimulant-positive samples during the study period. Since no numerical results for this outcome are reported in the registry record, the record cannot establish the direction, size, or statistical precision of a treatment contrast. It also does not report a single primary comparison derived from the outcome's several categories or time points.
3. Trial Design
This was a randomized, parallel-group trial with doxazosin extended release compared with placebo. The registry lists the trial as phase 1 and phase 2, with an enrollment of 22. The sponsor was the University of Arkansas. The record lists the study as completed, with a start date of 2011-06 and primary completion date of 2014-05.
The planned treatment period is described as 8 weeks in the brief summary. Doxazosin was initially administered at 4 mg/day, with an increase to 8 mg/day on day 8. The placebo arm was maintained on cellulose throughout the trial. The registry identifies masking as triple, while the brief summary calls the study double blind. The identities of the masked roles and an explanation for the difference in those descriptions are not reported in the registry record.
The primary outcome is titled “Change in Psychostimulant-positive Urines Over Time.” Urine drug screens were collected twice weekly and assessed for methamphetamine or cocaine. The stated primary-outcome population consists of eligible participants who received at least one dose of study medication. The record does not specify how many randomized participants received medication, completed follow-up, or contributed outcome data at each time point.
Although the record identifies randomization and masking, it does not report the randomization procedure, allocation concealment, or the practical procedures used to maintain masking. It also does not report the statistical analysis plan, the planned primary contrast, or a sample-size justification for the trial. A planning illustration based on the observed effect is distinct from the design rationale for this completed study; the trial's own design justification is not reported in the registry record.
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.
Overall Study
| Stage | Doxazosin | Placebo |
|---|---|---|
| STARTED | 11 | 11 |
| COMPLETED | 3 | 2 |
| NOT COMPLETED | 8 | 9 |
Reasons for not completing this period:
| Reason | Doxazosin | Placebo |
|---|---|---|
| Lost to Follow-up | 5 | 8 |
| was arrested and put in jail | 0 | 1 |
| non study related adverse event | 1 | 0 |
| Blood Pressure outside study parameters | 2 | 0 |
Analysis population for the primary outcome, as defined in the registry: Those eligible participants who received at least one dose of study medication.
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.
Population: Those eligible participants who received at least one dose of study medication.
| Characteristic | Unit | Doxazosin | Placebo | Total |
|---|---|---|---|---|
| Participants analysed | 11 | 11 | 22 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 11 | 11 | 22 |
| Age, Categorical: >=65 years | Participants | 0 | 0 | 0 |
| Sex: Female, Male: Female | Participants | 4 | 6 | 10 |
| Sex: Female, Male: Male | Participants | 7 | 5 | 12 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Asian | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Black or African American | Participants | 5 | 4 | 9 |
| Race (NIH/OMB): White | Participants | 6 | 7 | 13 |
| Race (NIH/OMB): More than one race | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 0 | 0 | 0 |
| Region of Enrollment: United States | participants | 11 | 11 | 22 |
6. Primary Endpoint
The registry lists the primary outcome as Change in Psychostimulant-positive Urines Over Time, measured over twice-weekly urine samples (8 weeks).
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Deviation |
| Unit | proportion of psychostimulant-pos urines |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is a repeated urine-based measure of stimulant use: the proportion of urine samples positive for methamphetamine or cocaine over time. Samples were collected twice weekly during the 8-week trial. The registry description says weekly urine results were averaged within each participant, then the mean proportion across participants in each group was calculated for graphic representation.
This endpoint uses a biological measure rather than relying only on participants' reports of use. A positive screen records detection of either named stimulant in a collected sample. The proportion expresses the positive samples relative to the samples considered for a participant, while the group mean describes the average participant-level proportion. This is a continuous summary measure, even though the underlying urine results are positive or negative. In general, repeated measurements can describe a pattern during follow-up rather than a single observation at one moment.
The endpoint title refers to change over time, but the registry record does not report numerical values for the outcome, a definition of a specific baseline-to-follow-up change, or a single group contrast. It therefore does not provide enough information to describe the observed trajectory, estimate a treatment difference, or assess the precision of that difference. Handling of missed or unavailable urine samples is not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies a clinically relevant measurement strategy: repeated urine screens for methamphetamine or cocaine during treatment, summarized as proportions. It also identifies the treatment groups and an analysis population for the primary outcome. However, it does not give the primary outcome values, group estimates, a treatment-effect estimate, a confidence interval, or a p-value. Consequently, the posted information does not quantify whether the groups differed, in which direction they differed, or how precisely any difference was estimated.
The outcome title emphasizes change over time, and the description indicates that weekly results were averaged within participants before group-level means were calculated for graphic representation. Repeated observations from the same participant are related, so they should not automatically be treated as independent observations. An analysis of a time pattern may also need to address how effects vary across follow-up. The registry does not report the inferential method used for these measurements, or whether the graphic summaries were accompanied by a model-based or other statistical comparison.
The record states that the primary outcome has several categories or time points and was not reduced to one comparison. That matters for interpretation: a set of results across time cannot be replaced by a single treatment-effect claim without specifying which contrast or overall summary is being assessed. The registry record does not describe how the investigators selected or tested comparisons across time, nor does it report a multiplicity adjustment. These omissions prevent a reader from determining whether any particular time-point finding was prespecified, how uncertainty was evaluated, or how multiple comparisons were handled.
Numerical safety summaries are available separately. The registry lists one serious adverse event among 11 participants at risk in the doxazosin group and none among 11 at risk in the placebo group. It lists other adverse events for 8 of 11 at risk in the doxazosin group and 4 of 11 at risk in the placebo group. These are descriptive counts in a small enrolled trial, not estimates of a precise comparative safety effect. The registry also names suicidal ideation as a top serious-event term at 9.1%; event-level detail and any analysis of between-group safety differences are not reported in the registry record.
Overall, the posted results support a description of the design, endpoint, and reported adverse-event counts, but not a quantitative conclusion about the primary outcome. In the absence of endpoint estimates and their uncertainty, neither the size nor the reliability of a treatment contrast can be judged from the registry record.
9. Statistical Methods Explained
What kind of measure is the primary outcome? The registry classifies the endpoint as a mean of a continuous measure, with standard deviation as the stated dispersion. The underlying observations are urine screens, each recorded as positive or negative for methamphetamine or cocaine. The endpoint then summarizes the proportion positive for each participant and describes group means. In general, reporting a mean together with a standard deviation gives information about both the average and the spread of participant-level measurements. The registry record does not provide the actual mean or standard deviation values.
Why summarize repeated samples? Multiple urine samples during follow-up can reflect a pattern of stimulant-positive tests over the treatment period. Averaging weekly results within each participant gives each participant a summary for that period, and calculating a group mean describes the average of those participant-level summaries. This approach is distinct from treating every sample as if it came from a different person. In general, repeated measurements from one person tend to be related, so analyses that use all observations need to account for that within-person dependence. The registry describes the averaging used for graphic representation but does not state how repeated measures were handled in inferential testing.
What does a confidence interval mean? In general, a confidence interval expresses the statistical uncertainty around an estimated quantity under the assumptions of the method used. A narrower interval indicates greater precision than a wider interval, while an interval that includes values on both sides of a no-difference value may be compatible with several possible effects. Interpretation depends on the outcome scale and the contrast being estimated. No confidence interval for the primary outcome is reported in the registry record, so its precision cannot be assessed.
What does a p-value answer? In general, a p-value measures how unusual data at least as incompatible with a specified null hypothesis would be, if that hypothesis and the analysis assumptions held. It does not measure the size or clinical importance of an effect, nor does it give the probability that a treatment works. The registry record does not report a primary-outcome p-value or identify the test or model used to produce one. A p-value alone, even if available, would not replace an effect estimate and its uncertainty.
Why does the planned comparison matter? A treatment effect needs a defined contrast, such as a comparison between group averages at a specified time or an overall comparison across follow-up. The primary outcome is described as change over time and includes several categories or time points; the record says it was not reduced to one comparison. Without the exact contrast and analysis method, the direction and magnitude of any single treatment effect cannot be reconstructed from the endpoint description. The statistical model, adjustment variables, and handling of baseline measurements are not reported in the registry record.
How should sample-size illustrations be understood? In general, a planning calculation estimates how many participants would be needed under assumptions about the target effect, variability, significance level, allocation, and statistical method. Such a calculation is not a measure of the trial's observed power and does not substitute for the results. The stated planning assumptions use a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the target effect defined as a stated fraction of the observed effect. The illustration is based on the observed effect, rather than being the trial's own design justification. It should therefore be read as planning context, not as a description of the study's original sample-size rationale. That rationale is not reported in the registry record.
What does over-dispersion mean in general? For outcomes analyzed with a model that assumes a particular variance pattern, over-dispersion means the observed variability is greater than the model expects. If not accounted for, standard errors may be too small and uncertainty may appear understated. The registry record does not identify a count model or report an over-dispersion assessment for this continuous proportion endpoint, so this is general statistical context rather than a claim about the trial's analysis.
What is needed to evaluate the reported outcome? A fuller statistical interpretation would require participant-level or group-level outcome summaries over time, an explicit treatment contrast, and measures of uncertainty. It would also require the analysis population, rules for unavailable samples, and the method used to account for repeated observations and any multiple comparisons. These details are not reported in the registry record. Accordingly, the endpoint can be described, but its treatment comparison and statistical precision cannot be evaluated from the posted results.
10. Multiplicity, Missing Data and Analysis Populations
The primary outcome is described across several categories or time points, and the registry record indicates that it was not reduced to one comparison. This creates an interpretive issue: multiple time-specific comparisons can generate a collection of findings, while a single overall conclusion requires a defined summary or test. The record does not identify a primary time point, an overall repeated-measures contrast, or a multiplicity strategy. Whether the analyses used an adjustment or another prespecified approach is not reported in the registry record.
Missing urine samples could affect a proportion-based endpoint because the number and timing of samples considered contribute to the summary. The registry record does not report how missed visits, unavailable specimens, or incomplete follow-up were handled. It does not describe imputation, exclusion rules, sensitivity analyses, or the amount of missing outcome data. These details are needed to judge whether the calculated summaries represent all planned observations or only available samples.
The primary-outcome population is specified as eligible participants who received at least one dose of study medication. This describes an exposed-participant population, but the registry does not say whether an intention-to-treat analysis was also conducted, or how participants were analyzed if they discontinued treatment or missed follow-up. The analysis population used for the reported safety counts is described by participants at risk in each group; the relationship between that population and all randomized participants is not further detailed.
These omissions do not establish that a particular method was or was not used. They mean the relevant analysis choices are not reported in the registry record, limiting assessment of the robustness and completeness of the primary-outcome findings.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Doxazosin | 1 | 11 | 9.1% |
| Placebo | 0 | 11 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Doxazosin | 8 of 11 |
| Placebo | 4 of 11 |
Most frequent serious adverse event terms
| Event term | Organ system | Doxazosin | Placebo |
|---|---|---|---|
| Suicidal Ideation | Psychiatric disorders | 1 of 11 | 0 of 11 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Doxazosin | Placebo |
|---|---|---|---|
| Headache | Nervous system disorders | 1 of 11 | 2 of 11 |
| nausea, abdominal cramps | Gastrointestinal disorders | 1 of 11 | 1 of 11 |
| Drowsiness, Fatigue | General disorders | 1 of 11 | 1 of 11 |
| Sleep Disturbances | General disorders | 1 of 11 | 1 of 11 |
| Elevated blood pressure | Cardiac disorders | 2 of 11 | 0 of 11 |
| Muscle Pain | Musculoskeletal and connective tissue disorders | 1 of 11 | 0 of 11 |
| Numbness in fingertips | Nervous system disorders | 1 of 11 | 0 of 11 |
| black eye | Eye disorders | 1 of 11 | 0 of 11 |
| palpitations with shortness of breath | Psychiatric disorders | 1 of 11 | 0 of 11 |
| Sweating | General disorders | 0 of 11 | 1 of 11 |
Serious events with the highest arm-level rate: suicidal ideation (9.1%).
The registry lists serious adverse events for 11 participants at risk in each group. One participant in the doxazosin group was affected, compared with none in the placebo group. The registry names suicidal ideation as a top serious-event term at 9.1%. It does not provide a full serious-event breakdown or report a statistical comparison between groups.
For other adverse events, the record lists 8 affected participants among 11 at risk in the doxazosin group and 4 among 11 at risk in the placebo group. These counts describe the posted safety summaries; they do not indicate how many events each participant experienced or how long each participant was observed. The registry record does not report definitions for the “other” category or event-level details for all affected participants.
Small group counts can make safety summaries imprecise, and a difference in observed counts does not by itself establish a causal treatment effect. No deaths are listed as a numerical result; death information is not reported in the registry record. The safety figures should therefore be read as descriptive records of affected participants, not as a definitive comparison of risk.
12. What the Result Does, and Does Not, Mean
The registry record establishes that a randomized, placebo-controlled study of doxazosin extended release was conducted in participants with methamphetamine or cocaine dependence, and that the primary outcome focused on urine-positive proportions over time. It also reports adverse-event counts by group. These registry entries describe the design and the outcomes collected; they do not provide a numerical primary efficacy result.
Because group outcome values, a treatment-effect estimate, a confidence interval, and a p-value are not reported in the registry record, the direction and magnitude of the primary outcome cannot be determined from the posted information. There is no basis in the record for saying how much the groups differed, whether a difference was statistically distinguishable from no difference, or how precise an estimate might be. The outcome's several time points also mean a single conclusion would require a specified comparison that is not reported.
The safety counts likewise should not be treated as proof of a comparative safety effect. They show the number of participants listed as affected in each group, but do not provide a statistical analysis, detailed event timing, or a full account of event severity beyond the serious-event classification. The suicidal ideation term is listed at 9.1%, but no additional interpretation of that percentage is reported in the registry record.
In general, a completed trial can still have results that are not sufficiently reported in its registry entry to support an assessment of treatment effect. The record's completed status does not fill in missing outcome estimates or analysis methods. The appropriate conclusion from the posted information is therefore limited: the trial's endpoint and some safety counts are described, while its quantitative primary-outcome result and inferential interpretation are not reported in the registry record.
13. Why This Trial Matters Statistically
This trial is statistically informative as an example of the gap between defining an outcome and reporting an interpretable treatment estimate. The record specifies a repeated biological measure, summarizes how weekly urine results were averaged, and identifies the outcome population. Those elements help readers understand what was intended to be measured. Yet without numerical group results, a contrast, and uncertainty, the main endpoint cannot be assessed quantitatively.
The repeated-measure structure also matters. Samples are collected over time from the same participants, so a time-course analysis raises questions about dependence among observations, the treatment contrast of interest, and the handling of incomplete follow-up. The registry does not report the inferential approach or missing-data rules. Clear reporting of these methods would help readers distinguish descriptive trajectories from an adjusted or model-based test of treatment differences.
The stated planning illustration is another useful distinction. A calculation based on an observed effect can illustrate the sample size associated with specified planning assumptions, but it is not evidence that the trial was designed with those assumptions and is not observed power. The original sample-size justification is not reported in the registry record. Keeping design rationale separate from a retrospective illustration prevents the planning calculation from being mistaken for a feature of the trial protocol.
Finally, the safety information is expressed as participant counts and a listed serious-event term. These summaries are useful for describing what the record reports, but the small group counts and lack of comparative analysis limit inference. Together, the missing primary estimates and analysis details show why complete numerical reporting is essential for readers to evaluate statistical evidence, independently of whether a study is listed as completed.
14. 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.
The main limitation for interpreting efficacy is that the registry record does not report numerical results for the primary outcome. It gives no group means, standard deviations, treatment-effect estimate, confidence interval, or p-value. Without these, the size, direction, and precision of the primary comparison cannot be assessed.
The endpoint spans repeated urine samples and several time points, but a single comparison is not reported. The statistical model, handling of correlation among repeated observations, multiplicity approach, and missing-sample rules are not reported in the registry record. The outcome population is described as eligible participants who received at least one dose, but the number contributing data and the handling of participants with incomplete follow-up are not stated.
The enrollment was 22, and the adverse-event summaries list 11 participants at risk in each group. The record does not provide enough detail to establish how the primary-outcome analysis population relates to all randomized participants. Participant characteristics, treatment adherence, withdrawals, and the completeness of urine collection are not reported in the registry record. These are relevant details for understanding who contributed to the endpoint and how representative the observed data may be.
The descriptions of masking differ: the registry lists triple masking, while the brief summary describes the trial as double blind. The record does not explain the difference or identify the masked roles. It also does not report the trial's own sample-size justification. These limits are specific to the available registry description and should not be filled in by assumptions about common trial practice.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Doxazosin for Psychostimulant Dependence — NCT01371851.
- Registry record last updated 2015-07-27; status last verified 2015-07.
- Results first posted 2015-07-27.
- 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.
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18. Record Summary
The registry record describes a completed, randomized, parallel-group phase 1 and phase 2 trial of doxazosin extended release versus placebo for methamphetamine or cocaine dependence. Enrollment was 22. The planned regimen began at 4 mg/day and increased to 8 mg/day on day 8; the placebo group received cellulose throughout the 8-week trial.
The primary endpoint was the proportion of urine samples positive for methamphetamine or cocaine over time, based on twice-weekly screens. The outcome population is described as eligible participants who received at least one dose. Numerical primary-outcome results and a single treatment comparison are not reported in the registry record. Safety summaries list serious and other adverse events by group, including suicidal ideation as a top serious-event term at 9.1%. Details of the statistical analysis, missing-data handling, multiplicity, and trial sample-size justification are not reported in the registry record.