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 Mirtazapine to Reduce Methamphetamine Use Among MSM With High-risk HIV Behaviors (NCT00497081), a randomized phase 2 study. The primary outcome is Change in Number of Positive Methamphetamine Urine Tests, Comparing Baseline (Week 0) to Final Visit (Week 12)..
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00497081 |
| Phase | Phase 2 |
| Condition | Substance Abuse, HIV Infections |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Quadruple |
| Enrollment | 60 |
| Arms in the primary outcome | 2 |
| Lead sponsor | San Francisco Department of Public Health |
| Results posted | Yes |
2. Clinical Question
Population
Men who have sex with men (MSM) with high-risk HIV behaviors and methamphetamine use were the intended population. The registry record lists substance abuse and HIV infections as conditions, but it does not specify that participants had HIV infection.
Intervention
The intervention was mirtazapine, described as 30 mg daily. The study aimed to assess whether it reduced methamphetamine use during follow-up.
Comparator
The comparator was placebo, also described as 30 mg daily. The record labels the arms as active comparator and placebo comparator.
Primary question
The primary endpoint was the change in the number of positive methamphetamine urine tests from baseline at week 0 to the final visit at week 12, expressed as percentage reduction. The central clinical research question was whether this measure differed between the mirtazapine and placebo groups.
This framing describes the study question, not a conclusion about treatment. A randomized comparison is intended to assess whether outcomes differ between assigned groups, but an interpretable answer requires a reported between-group estimate and information about its uncertainty. The registry record gives arm-level endpoint values, but it does not report a comparative estimate, confidence interval, or analysis result for the primary outcome.
The study is identified as phase 2 and randomized, with a parallel-group design and quadruple masking. Its brief summary describes an intermediate-size study with 3 months of follow-up. Those descriptions set the context for the question, but do not establish which statistical model was used, how missing observations were handled, or whether the posted arm-level values reflect all randomized participants.
3. Trial Design
The registry describes a randomized, parallel-group, quadruple-masked phase 2 trial. Participants were assigned to mirtazapine or placebo. The intervention descriptions specify mirtazapine 30 mg daily and placebo 30 mg daily. The record does not identify which participant, clinician, investigator, or assessor roles were included in quadruple masking, nor does it report the allocation method beyond saying that allocation was randomized.
The registry enrollment field is 60. The two reported outcome groups each list 30 participants. These are record entries; the record does not clarify whether the group counts represent everyone randomized, everyone analyzed, or participants with endpoint observations. The analysis population and handling of participants who did not complete follow-up are not reported in the registry record.
The primary endpoint compares baseline, defined as week 0, with the final visit at week 12. The brief summary characterizes follow-up as 3 months. The record lists the study status as completed, a start of 2007-05, and primary completion of 2010-03. The sponsor is the San Francisco Department of Public Health.
A parallel design compares outcomes from groups assigned to different treatments over the study period. Randomization can support a fair comparison when the analysis preserves the assigned groups and appropriately handles incomplete data. However, the registry record does not report the randomization procedure, concealment details, adherence, co-interventions, or analysis approach. It also does not provide a protocol rationale for the enrollment target. These unreported details limit what can be concluded about execution and analysis from the registry entries alone.
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 | Active Comparator: | Placebo Comparator: |
|---|---|---|
| STARTED | 30 | 30 |
| COMPLETED | 28 | 28 |
| NOT COMPLETED | 2 | 2 |
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.
| Characteristic | Unit | Active Comparator: | Placebo Comparator: | Total |
|---|---|---|---|---|
| Participants analysed | 30 | 30 | 60 | |
| Age, Continuous | years | 40.9 (SD 8.0) | 40.1 (SD 10.1) | 40.5 (SD 9.0) |
| Sex: Female, Male: Female | Participants | 0 | 0 | 0 |
| Sex: Female, Male: Male | Participants | 30 | 30 | 60 |
| Race/Ethnicity, Customized: White | participants | 18 | 19 | 37 |
| Race/Ethnicity, Customized: African American | participants | 6 | 5 | 11 |
| Race/Ethnicity, Customized: Latino | participants | 3 | 4 | 7 |
| Race/Ethnicity, Customized: Other | participants | 3 | 2 | 5 |
6. Primary Endpoint
The registry lists the primary outcome as Change in Number of Positive Methamphetamine Urine Tests, Comparing Baseline (Week 0) to Final Visit (Week 12)., measured over Baseline (week 0) and Final Visit (week 12).
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | Percentage reduction |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is the change in the number of positive methamphetamine urine tests between baseline at week 0 and the final visit at week 12. The unit is percentage reduction. Urine testing provides an objective measure of methamphetamine detection at the times samples are collected; comparing results over time is intended to capture change in detected use during follow-up.
The registry reports a 40.0 percentage reduction for the mirtazapine arm and a 6.0 percentage reduction for the placebo arm. These are arm-level endpoint values. They do not, on their own, describe the variation among participants or establish the size and precision of a treatment-group contrast. The record does not report the number of urine tests collected per participant, the distribution of positive tests, or the method used to calculate the percentage reduction.
As a general statistical consideration, a baseline-to-final change measure condenses information from two assessment points. It does not show the pattern of observations between those points, and the result can depend on how incomplete or unavailable tests are handled. The registry record does not report those handling rules. It also does not provide a confidence interval or a statistical test for the primary comparison. Thus, the endpoint definition explains what the trial intended to measure, while the posted summaries alone do not provide a complete estimate of the comparative effect.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The posted primary outcome values are 40.0 percentage reduction in positive methamphetamine urine tests for the mirtazapine arm and 6.0 percentage reduction for the placebo arm. The endpoint is defined as change between baseline at week 0 and the final visit at week 12. These figures describe the arm-level summaries recorded for that outcome; they should not be read as percentages of participants who stopped using methamphetamine, or as percentages of participants with negative urine tests.
The registry record does not report a between-arm effect estimate, confidence interval, or p-value for the primary endpoint. It also marks the two-arm comparison as not estimable for this count-other endpoint. Consequently, the posted values do not establish how precisely the groups differed, whether the observed arm-level pattern is compatible with chance variation, or whether an adjusted comparison would produce a different result. No comparative conclusion should be substituted for the analysis that is absent from the record.
The group entries list 30 participants in each arm. The registry does not clarify whether these are randomized, treated, or analyzed participants, and it does not say how many contributed measurements at both visits. The uncertainty around each group’s result therefore cannot be reconstructed from the arm sizes alone. No variability measure, participant-level distribution, or missing-data summary is reported for this endpoint.
In general, an arm-level change can help describe what was observed in each group, but the causal question concerns the contrast between assigned groups. A direct comparison should account for the trial design and the outcome data, and should report both an effect estimate and its uncertainty. Without those items, the reader cannot judge the precision of the contrast from the registry record. The absolute values also cannot show whether the result was consistent across participants or driven by a small number of observations.
The brief study summary states that the trial was intended to assess mirtazapine’s effect on methamphetamine use among high-risk MSM. Intent and posted results are distinct: the aim does not establish that the intervention caused a change. The registry status is completed, but completion status is not evidence of a particular outcome. No secondary outcome results are posted, and no analyses are listed. The primary result should therefore be described as an arm-level summary with no reported inferential comparison, rather than as a definitive finding for or against the intervention.
Planning calculations based on a fraction of an observed effect, when considered, are illustrations for future study design rather than evidence about this trial’s statistical power. They do not replace the missing uncertainty estimate, and they are not observed power. The registry record does not report the trial’s own sample-size justification or analysis plan, so the relationship between the enrollment and the planned precision cannot be assessed from this record.
9. Statistical Methods Explained
The record identifies a randomized, parallel-group comparison and a count-related primary outcome expressed as percentage reduction. It does not report the statistical test or model used to analyze that outcome. The method should therefore not be inferred from the endpoint label or from the two arm-level values. The explanation below describes general statistical principles relevant to this kind of endpoint, not a claim about the analysis performed in this trial.
What does an arm-level value tell us?
An arm-level summary describes the observed outcome within a group. Here, the reported endpoint values are 40.0 percentage reduction for mirtazapine and 6.0 percentage reduction for placebo. A comparison of treatment groups requires an estimate of the contrast between those summaries, or another contrast suited to the analysis. The registry record does not report that estimate. Nor does it provide a confidence interval, which in general expresses the range of values compatible with the data and analysis under the method’s assumptions.
A confidence interval is useful because an estimate without uncertainty can give an incomplete picture. A narrow interval generally indicates greater precision under the chosen model, while a wide interval indicates less precision. The interval does not remove uncertainty or by itself establish clinical importance. No interval is reported for this primary comparison, so the precision of a between-arm effect cannot be assessed from the record.
Why can count outcomes need careful modeling?
Counts can vary in ways that make a simple model unsuitable. In general, a count model often begins with assumptions about how the mean and variability of counts relate. If the observed variation is greater than the model allows, a condition called over-dispersion, standard errors may be too small and confidence intervals or tests may be misleading. Other features can matter too, including repeated observations within a participant, many zero counts, or unequal observation opportunities. These are general considerations, not reported properties of this trial’s data.
The endpoint is framed as a change in the number of positive urine tests, summarized as a percentage reduction. The registry record does not report the underlying test counts, how many observations were expected or obtained per participant, or whether the count was modeled directly. It also does not say whether the analysis used baseline adjustment, a repeated-measures model, a transformation, or another method. Without the analysis details and data structure, it is not possible to determine which assumptions were used or whether they were appropriate.
Why does the comparison need to reflect randomization?
In general, randomization supports comparisons between groups assigned to different treatments. A treatment-effect analysis commonly aims to preserve that comparison by analyzing participants according to assigned group, while specifying how missing outcomes and protocol departures are handled. Other analysis populations may be defined for particular purposes, but their definitions should be stated. The registry record does not report an analysis population, and the arm counts do not establish who was included in the primary analysis.
Baseline-to-final change can be analyzed in more than one way. A direct comparison of changes is one possibility; an analysis of final outcomes adjusted for baseline is another. Repeated assessments may call for a method that accounts for measurements from the same participant being related. In general, the method and its assumptions affect the estimate and its uncertainty. The record supplies no model description or analysis results with which to determine the approach used in this trial.
What is the role of significance testing?
A significance test, when specified, evaluates how compatible the observed data are with a stated null hypothesis under a statistical model. A p-value does not measure the probability that the null hypothesis is true, the size of an effect, or its clinical importance. A p-value also does not replace an effect estimate and confidence interval. No primary-outcome p-value is reported in the registry record, so significance cannot be assessed from the posted endpoint summaries.
The planning assumptions describe illustrations using a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the effect to detect expressed as a fraction of the observed effect. These are planning assumptions, not evidence that the trial used the same analysis or was designed with that method. The registry record does not report a trial-specific sample-size justification. Any planning illustration is distinct from observed power; sample-size calculations for future studies should not be interpreted as a probability that this completed trial detected an effect.
What can be concluded from the posted analysis status?
The record lists no analyses and says that a two-arm comparison is not estimable for this count-other endpoint. This means the arm summaries cannot be turned into a reported inferential comparison using the registry information. It would be inappropriate to fill that gap by choosing a test and calculating a new result from incomplete summary data. A valid reanalysis would require sufficient outcome information and a defensible prespecified or clearly described method.
In general, transparent reporting would include the analysis population, outcome definition, model or test, effect estimate, measure of uncertainty, and handling of missing observations. For count data, reporting the observation structure and relevant model assumptions can help readers assess whether the analysis fits the data. Those details are not reported in the registry record for this trial’s primary comparison. The available values remain descriptive arm-level summaries, not a complete statistical analysis of the treatment contrast.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists three outcome measures, but it does not post secondary outcome results. It lists no analyses, and the primary two-arm comparison is not estimable in the record. A multiplicity plan—how the analysis would account for testing more than one outcome or comparison—is not reported in the registry record. It is therefore not possible to determine whether any adjustment was planned or used, or how any secondary findings should be interpreted relative to the primary endpoint.
Missing-data handling is also not reported. The registry does not state how absent urine tests, missed final visits, or incomplete endpoint records were treated. The group entries each list 30 participants, but the record does not clarify whether those counts are the randomized groups or the analysis denominators. It gives no missingness counts, reasons for missing observations, imputation method, or sensitivity analysis.
The analysis populations are not reported in the registry record. In general, readers need to know whether the analysis followed randomized assignment, included only participants who completed treatment, or used another defined population. These choices can affect interpretation, especially when outcomes are unavailable for some participants. The record also does not report an interim-analysis plan, stopping rules, or a statistical analysis plan. Their absence from the registry record should not be taken as evidence that a particular procedure was or was not used outside the record.
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 |
|---|---|---|---|
| Active Comparator: | 1 | 30 | 3.3% |
| Placebo Comparator: | 1 | 30 | 3.3% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Active Comparator: | 27 of 30 |
| Placebo Comparator: | 24 of 30 |
Most frequent serious adverse event terms
| Event term | Organ system | Active Comparator: | Placebo Comparator: |
|---|---|---|---|
| Compression (spine) | Injury, poisoning and procedural complications | 0 of 30 | 1 of 30 |
| Meth-induced Psychosis | Psychiatric disorders | 1 of 30 | 0 of 30 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Active Comparator: | Placebo Comparator: |
|---|---|---|---|
| Increased ALT | Hepatobiliary disorders | 7 of 30 | 9 of 30 |
| Drowsiness | Nervous system disorders | 13 of 30 | 0 of 30 |
| Increased AST | Hepatobiliary disorders | 5 of 30 | 8 of 30 |
| Skin and Soft Tissue Infection | Infections and infestations | 3 of 30 | 7 of 30 |
| Gastroenteritis | Gastrointestinal disorders | 4 of 30 | 4 of 30 |
| Hyperglycemia | Metabolism and nutrition disorders | 4 of 30 | 3 of 30 |
| Upper Respiratory Infection | Respiratory, thoracic and mediastinal disorders | 3 of 30 | 4 of 30 |
| Hyperbilirubinemia | Hepatobiliary disorders | 2 of 30 | 4 of 30 |
| Increased Alkaline Phosphatase | Hepatobiliary disorders | 1 of 30 | 4 of 30 |
| Gonorrhea | Infections and infestations | 3 of 30 | 1 of 30 |
Serious events with the highest arm-level rate: compression (spine) (3.3%), meth-induced psychosis (3.3%).
For serious adverse events, the registry lists 1 affected participant among 30 at risk in the mirtazapine arm and 1 among 30 at risk in the placebo arm. The record does not report deaths. These entries describe the reported counts and denominators; they do not by themselves establish whether the events were caused by treatment or whether the groups differed in safety.
The serious-event terms listed are Compression (spine) and Meth-induced Psychosis, each reported as 3.3%. The record does not clearly map these terms to an individual treatment arm, so they should not be assigned to a particular group based on the information available. A term’s listing also does not establish causality, severity beyond its registry classification, timing, or whether it occurred in a participant counted elsewhere.
Other adverse events are listed for 27 participants at risk of 30 in the mirtazapine arm and 24 at risk of 30 in the placebo arm. These are separate registry counts from the serious-event entries. The record does not provide further definitions, event-level detail, duration, or comparative statistical analysis. Safety counts are descriptive and should be read in light of the reporting information and the limited follow-up described for the study.
12. What the Result Does, and Does Not, Mean
The registry record describes a randomized, quadruple-masked phase 2 study comparing mirtazapine with placebo among MSM with high-risk HIV behaviors. Its primary endpoint concerns percentage reduction in positive methamphetamine urine tests from baseline at week 0 to the final visit at week 12. The recorded arm-level values are 40.0% for mirtazapine and 6.0% for placebo.
Those figures indicate what the record reports for each group’s endpoint summary. They do not mean that 40.0% of participants in the mirtazapine group stopped using methamphetamine, nor that 6.0% of placebo participants did so. The outcome is a reduction in positive tests, not a participant-level cessation measure. The record does not provide the underlying counts or individual-level outcomes needed to characterize who changed or how consistently.
The figures also do not establish a statistically supported difference between treatment groups. No comparative estimate, confidence interval, or p-value is reported for the primary endpoint, and the registry marks the two-arm comparison as not estimable. Thus the posted results do not quantify the uncertainty around the apparent arm-level contrast. They also do not establish causation, clinical importance, or whether the observed pattern would be reproduced in another study.
The absence of posted analyses and secondary results does not establish that no analyses were performed outside the registry. It means the registry record does not provide them for interpretation. Similarly, completion status and the stated study objective describe the trial’s status and intent, not the efficacy of the intervention. The sound conclusion is limited: the record contains arm-level primary endpoint summaries and safety counts, but it does not contain enough statistical reporting to make a precise comparative assessment.
13. Why This Trial Matters Statistically
This trial illustrates why descriptive group summaries and a treatment-effect analysis are not interchangeable. The registry reports a percentage reduction for each arm, but a clinical research question about treatment comparison requires an estimate of the contrast and an account of its uncertainty. Without those elements, readers cannot judge the precision of the apparent difference or how strongly the data support a comparative interpretation.
The endpoint also highlights the importance of defining the measurement and its analysis together. A count of positive urine tests, summarized as a percentage reduction between baseline and a final visit, can depend on the number and timing of tests, the baseline values, and how missing observations are handled. These details are not reported in the registry record. For count outcomes generally, the model should reflect the way observations are collected and their variability; over-dispersion and repeated measurements may matter depending on the data.
Reporting the analysis population, missing-data approach, and prespecified statistical method is important for understanding whether the result aligns with randomized assignment and the intended endpoint. The record does not provide those details, or a primary comparison, and it lists no secondary analyses. This makes the trial a useful example of the limits of interpreting outcome summaries without the accompanying analysis.
Planning calculations have a different purpose from outcome reporting. Illustrations based on an observed effect can inform future study planning under stated assumptions, but they cannot supply missing evidence about the precision or significance of this completed trial. The registry record does not report the trial’s own sample-size justification. Keeping planning assumptions separate from observed results is therefore essential to an accurate statistical reading.
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 registry record leaves important details about the primary endpoint and its analysis unspecified. It reports arm-level percentage reductions but does not provide the underlying positive-test counts, the number of tests per participant, the distribution of outcomes, or a measure of variability. It also does not report a between-group estimate or confidence interval. The primary comparison is marked as not estimable, so the main treatment contrast cannot be assessed statistically from the posted results.
The record does not explain how the percentage reduction was calculated, including how participants with unavailable baseline or final measurements were handled. Although each arm lists 30 participants, it does not establish whether every listed participant contributed to the endpoint. Missing-data counts, reasons, and sensitivity analyses are not reported. The analysis population is also unspecified.
Important design and conduct details are not reported in the registry record, including the specific randomization procedure, the roles covered by quadruple masking, adherence, and any additional treatments. The protocol rationale and trial-specific sample-size justification are not reported. No statistical analysis plan, interim-analysis information, or multiplicity approach is given. These omissions limit assessment of the planned and conducted analysis, rather than proving that a procedure was absent.
The brief summary describes 3 months of follow-up, while the endpoint compares week 0 with week 12. The record does not provide additional outcome trajectories between those visits. Serious-event terms are listed without a clear arm mapping, and deaths are not reported. These limitations call for a restrained reading of both efficacy and safety summaries; they do not by themselves establish that the results are biased or that the trial was conducted improperly.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Mirtazapine to Reduce Methamphetamine Use Among MSM With High-risk HIV Behaviors — NCT00497081.
- Registry record last updated 2015-01-05; status last verified 2014-12.
- Results first posted 2014-10-20.
- 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
NCT00497081 is a completed, randomized, parallel-group, quadruple-masked phase 2 trial sponsored by the San Francisco Department of Public Health. It studied mirtazapine 30 mg daily versus placebo 30 mg daily among MSM with high-risk HIV behaviors. The registry lists enrollment of 60, with 30 participants in each outcome group, and describes follow-up as 3 months.
The primary endpoint was percentage reduction in the number of positive methamphetamine urine tests from baseline at week 0 to the final visit at week 12. The recorded arm-level reductions are 40.0% for mirtazapine and 6.0% for placebo. The registry does not report an inferential two-arm comparison, confidence interval, p-value, analysis population, or missing-data method. No analyses or secondary results are posted. Serious adverse events are listed for 1 participant in each arm; deaths are not reported in the registry record.