Genetic and Brain Mechanisms of Naltrexone's Treatment Efficacy for Alcoholism: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Genetic and Brain Mechanisms of Naltrexone's Treatment Efficacy for Alcoholism (NCT00920829), a randomized phase 4 study. The primary outcome is Percent Heavy Drinking Days by mu Opioid Receptor Gene.

2. Clinical Question

3. Trial Design

The registry record describes a randomized, triple-masked, factorial Phase 4 trial, with 358 participants enrolled. The study is marked completed and lists alcohol dependence as its condition. Its listed interventions are naltrexone and placebo, and its arm descriptions distinguish participants by OPRM1 genotype as well as medication assignment. Genotype is a participant characteristic, not a treatment assigned by investigators; the registry does not give further detail about how the factorial structure was implemented.

The naltrexone arms are described as receiving 50 mg after 2 days at 25 mg for 16 weeks. The A/A naltrexone arm description specifies medication management at 9 visits during 16 weeks. The placebo arm descriptions specify medication management during 16 weeks, although the Any G placebo description contains text referring to naltrexone dosing. That internal inconsistency prevents a confident reading of the described regimen for that arm.

The record says masking was triple, but does not identify which roles were masked or describe the masking procedures. It does not report the randomization sequence, allocation concealment, or the factorial allocation details. The study’s stated aims include treatment response, neuroimaging response to alcohol cues, possible mediation, and the relationship of compliance or adverse effects to treatment response. The record gives no detailed statistical plan explaining how those aims were analyzed.

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: A118G genotyping was performed for 355 of these, 259 were A/A (Asn40) allele and 96 were any G (asp). Of the 259 Asn40 subjects, 89 were selected to participate 5 met exclusion criteria and 7 were lost or declined. Of the 96 Asp subjects, 9 met exclusion; 12 were lost or declined.

Allocation

Reasons for not completing this period:

Available for Analysis

Reasons for not completing this period:

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 Percent Heavy Drinking Days by mu Opioid Receptor Gene, measured over Time Line Follow-Back drinking collected at each of 9 visits (weeks 1, 2, 3, 4, 6, 8, 10, 12 and 16).

The primary outcome is titled “Percent Heavy Drinking Days by mu Opioid Receptor Gene.” It is a continuous measure, expressed as a percentage of days, and is summarized as a mean with standard error. The registry describes drinking data as collected with Time Line Follow-Back at visits in weeks 1, 2, 3, 4, 6, 8, 10, 12 and 16. A definition of a heavy drinking day, including any threshold used, is not reported in the registry record.

As a general measurement concept, the proportion of days involving heavy drinking describes the frequency of this drinking pattern over a defined observation period. It can represent a treatment outcome in a way that reflects repeated drinking behavior rather than a single measurement. The registry title indicates that the outcome was considered by OPRM1 genotype, consistent with the trial’s stated interest in genetic differences in response. However, the outcome values, group comparisons, and precise analysis period are not reported in the registry record, so the magnitude or direction of any observed pattern cannot be described.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry labels the study randomized, triple-masked, and factorial. Randomization is a design method for assigning treatment in a way intended to reduce systematic differences between groups. Masking is intended to limit the influence of treatment knowledge on behavior, assessment, or interpretation. The record does not state which people were masked, how the randomization was carried out, or how the factorial design was operationalized, so those details cannot be evaluated.

The primary measure is continuous and reported as a mean with standard error. In general, a mean gives the central average of observed values, while a standard error describes the sampling precision of that average under a statistical model. Standard error is not the same as the spread of individual observations. A confidence interval, when reported, uses an estimate and its uncertainty to describe a range of values compatible with the data under the method’s assumptions. The registry record does not report confidence intervals or the underlying outcome estimates.

The outcome is a percentage of days and was collected repeatedly during follow-up. In general, repeated measurements on the same participant are correlated, so treating every observation as independent may understate uncertainty. Analyses of repeated outcomes can account for within-participant correlation and can estimate change over time or an average across specified visits. The registry record does not report the model used, how visits were incorporated, or whether the primary estimate concerns a particular visit, an average across visits, or another summary.

The trial’s genetic question concerns whether treatment response differs by OPRM1 genotype. In general, this is assessed through an interaction or a comparison of treatment effects across genotype groups. It is distinct from asking whether average outcomes differ by genotype regardless of treatment. The record does not report the exact contrasts, interaction estimate, or model specification. It also does not say whether genotype groups were defined before analysis or how genotype data were handled.

Because a percentage is bounded, general modeling considerations include whether the outcome distribution and residual behavior suit the chosen method. Repeated observations can also have different variability at different times or across groups. General methods may address such features through an appropriate outcome model or robust uncertainty estimates. The registry does not identify a model, diagnostics, variance assumptions, or any adjustment for the bounded nature of the measure. These are methodological considerations, not claims about what the investigators did.

The study’s broader aims include neuroimaging and mediation. In general, a mediation analysis asks whether a measured intermediate response may help account for an association between treatment and an outcome. Such analyses require a defined pathway and assumptions about relationships among treatment, mediator, and outcome. The registry record does not report the mediation method, its assumptions, or any results. It also does not report how compliance or adverse effects were incorporated into analyses; those post-randomization measures can require careful interpretation because they may relate to participant characteristics and treatment exposure.

The record states that two analyses were reported, but does not describe their methods. It does not identify whether estimates were adjusted, what covariates were included, how uncertainty was calculated, or whether any model-based assumptions were checked. There are no recalculated estimates in the available details to compare with sponsor analyses. Thus, the analysis approach cannot be independently assessed from the registry description, and no statistical result can be reconstructed from the endpoint title alone.

The sample-size assumptions describe a planning illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is described as a stated fraction of the observed effect. Such calculations are planning illustrations, not observed power and not evidence that the study was designed around a particular clinically important difference. The actual illustration values are not reported in the registry record. The registry also does not report the trial’s own sample-size justification, so the illustration should not be treated as that justification.

10. Multiplicity, Missing Data and Analysis Populations

The trial lists several scientific aims: treatment response by OPRM1 genotype, genotype-dependent effects on alcohol cue-induced brain activation, possible mediation, and relationships involving medication compliance or adverse effects. The record identifies one primary outcome measure and says that two analyses were reported, but does not describe how those analyses relate to the aims or which tests were designated primary. A multiplicity strategy, such as a hierarchy of hypotheses or adjustment for multiple comparisons, is not reported in the registry record.

When a study examines multiple outcomes, groups, time points, or interactions, interpreting an isolated statistical test can be difficult unless the testing plan is clear. This is a general issue: repeated testing can increase the chance of results that appear notable by chance. The registry’s primary outcome is collected at several visits, but it does not say how those visits were combined or whether separate visit-specific tests were performed. No correction method or prespecified testing sequence is reported.

Missing-data methods are not reported in the registry record. The record does not describe the amount or pattern of missing drinking assessments, how incomplete follow-up was handled, or whether any imputation or sensitivity analyses were used. The analysis populations are also not defined: it is not stated whether analyses included all randomized participants, participants with available outcome data, or another set. The enrollment figure alone does not establish the number included in any analysis.

These omissions limit evaluation of the reported analyses’ robustness and the scope of their conclusions. They do not show that a particular method was or was not used; they mean the registry record does not describe it.

11. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry lists serious adverse events and deaths by treatment and genotype group. It records zero participants affected by serious adverse events in each listed group. The numbers at risk for serious adverse events are 38 in Placebo/ASN, 35 in Placebo/ASP, 35 in Naltrexone/ASN, and 38 in Naltrexone/ASP. The record lists no serious adverse event terms.

Deaths are recorded as zero in Placebo/ASN, Placebo/ASP, and Naltrexone/ASN, and one in Naltrexone/ASP. The record does not give further information about the death, including its cause or relationship to treatment. These counts do not establish causality.

For other adverse events, the record lists affected counts of 16, 20, 30, and 29 in those same group orderings, with 38, 35, 35, and 38 at risk, respectively. The registry does not provide event types or severity details for these entries. Counts should be read as registry-reported affected participants, not as a measure of whether events were related to treatment or as a complete account of safety.

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

The record establishes that a randomized, triple-masked, factorial trial was conducted to study naltrexone, placebo, OPRM1 genotype, and alcohol-related outcomes. It identifies percent heavy drinking days by genotype as the primary outcome and describes repeated drinking assessments during 16 weeks. It also records aims involving brain response to alcohol cues, medication compliance, and adverse effects.

It does not provide the primary outcome values or estimates of treatment effects. Therefore, the direction and magnitude of any difference in heavy drinking days cannot be determined from this record. There is also no reported estimate of whether treatment response differed by genotype, no uncertainty interval for such an effect, and no reported result for the neuroimaging or mediation aims. These are missing results, not evidence of no effect.

The serious adverse event counts and other adverse event counts provide a limited description of recorded safety events by group. The record reports no participants affected by serious adverse events in the listed groups and records one death in Naltrexone/ASP. It does not provide details establishing a cause or treatment relationship. The other adverse event entries lack event descriptions, so their clinical meaning cannot be assessed from the counts alone.

More broadly, statistical significance, if reported elsewhere, would not by itself establish the importance or precision of an effect. Interpretation would require the estimates, uncertainty, analysis definitions, and appropriate context. Because those details are not reported in the registry record, no treatment conclusion or genotype-specific conclusion can be drawn from the information available.

13. Why This Trial Matters Statistically

This trial raises a statistically important question about whether a treatment effect may vary by a genetic characteristic. Such questions require more than comparing outcomes between genotype categories: the treatment contrast itself must be assessed across categories, with uncertainty made clear. The registry’s design and aims identify this question, while the absence of interaction estimates means the evidence cannot be evaluated from the record.

The study also links a behavioral outcome to a proposed biological pathway involving alcohol cue-related brain activation. Distinguishing treatment effects on behavior from treatment effects on a mediator, and assessing whether the mediator accounts for part of an effect, requires clearly specified models and assumptions. Those methods and results are not reported. The trial therefore illustrates why a stated mechanistic aim should not be confused with evidence that a mechanism was demonstrated.

Repeated drinking measurements create another relevant statistical issue. Measurements across visits can inform patterns over time, but the analysis must account for their relationship within participants and define how the visits contribute to the primary estimate. The registry identifies the measurement schedule but does not give the model or estimand.

Finally, interpreting a completed randomized trial requires more than its design label and enrollment count. Outcome estimates, uncertainty, analysis populations, missing-data handling, and the testing strategy are essential for judging what the results support. Their absence in the registry record sharply limits the conclusions that can be drawn about this trial.

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 primary endpoint is named and its measurement schedule is described, but its heavy drinking day definition is not reported in the registry record. The actual primary outcome means, standard errors, comparisons, and inferential results are also absent. This prevents assessment of effect direction, magnitude, and precision.

The arm descriptions contain an internal inconsistency: the Any G placebo arm is labeled placebo but its text describes naltrexone dosing. The record does not resolve which description is accurate. It also does not specify who was masked, how allocation was conducted, or the details of the factorial structure. These gaps make it difficult to reconstruct the trial procedures from the record alone.

The record does not describe the repeated-measures model, exact contrasts, covariate adjustment, missing-data approach, or analysis populations. It names several aims without reporting a multiplicity strategy or clarifying which tests were primary. For the broader mechanistic aims, methods and results for neuroimaging, mediation, and compliance analyses are not reported.

Safety information is limited to affected counts and numbers at risk, with no serious adverse event terms and no details about the recorded death. Other adverse event types and their treatment relationships are not reported. These limitations concern the information available in the registry record and do not establish what may appear in other study materials.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Genetic and Brain Mechanisms of Naltrexone's Treatment Efficacy for Alcoholism — NCT00920829.
• Registry record last updated 2018-07-10; status last verified 2018-06.
• Results first posted 2018-06-04.
• 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.

18. Record Summary

The registry record describes NCT00920829 as a completed, randomized, triple-masked, factorial Phase 4 study sponsored by the Medical University of South Carolina, with 358 participants enrolled. The condition is alcohol dependence, and the listed interventions are naltrexone and placebo.

The primary outcome is percent heavy drinking days by mu opioid receptor gene, summarized as a mean with standard error and assessed using repeated Time Line Follow-Back visits. The study’s stated aims include genotype-related treatment response, alcohol cue-induced brain activation, mediation, compliance, and adverse effects.

Primary outcome estimates, analysis details, missing-data methods, and multiplicity procedures are not reported in the registry record. The Any G placebo arm description is inconsistent with its label. Safety entries report no serious adverse events in the listed groups and one death in Naltrexone/ASP, without further detail.