Effects of Pioglitazone, a PPARgamma Receptor Agonist, on the Abuse Liability of Oxycodone: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Effects of Pioglitazone, a PPARgamma Receptor Agonist, on the Abuse Liability of Oxycodone (NCT01395784), a non-randomized phase 2 study. The primary outcome is Subjective Ratings of "Good" Drug Effect.

2. Clinical Question

The study asked whether subjective responses to oxycodone differed after maintenance on placebo or either of two pioglitazone doses in non-dependent people who misuse prescription opioids. Its primary focus was participants’ ratings of the good drug effect; other aims concerned analgesic, cognitive, and physiological responses.

The study therefore addresses a laboratory question about subjective responses under different maintenance conditions, rather than a clinical treatment outcome. Its stated aims do not establish what the outcome results were or whether the conditions differed.

3. Trial Design

This phase 2 study was completed and enrolled 32 participants. The registry classifies its allocation as non-randomized, its masking as single, and its model as crossover. A crossover design assesses outcomes under more than one condition across maintenance periods; the record describes outcome measures after placebo, pioglitazone 15 mg, and pioglitazone 45 mg maintenance. It does not report the sequence of conditions or how that sequence was determined.

Each maintenance period was described as lasting 2-3 weeks, with outcome measures collected during a laboratory session at its end. The primary outcome was peak subjective rating of oxycodone’s good drug effect. The stated secondary aims included analgesic, cognitive, and physiological effects; the listed secondary outcome is analgesic responses using the cold pressor test.

Non-randomized allocation matters when interpreting condition comparisons: differences may reflect the maintenance condition, but they may also be associated with the way participants entered or experienced conditions. The registry specifically cautions that the conditions are not a like-for-like control comparison. Although masking is identified as single, who was masked is not reported in the registry record. Details about the sequence, washout between periods, adherence, and changes in treatment are also not reported.

The registry gives the study start as 2010-08 and primary completion as 2014-01. These dates describe the study timeline, not the availability or quality of the outcome data. The record does not report numerical primary outcome estimates or analysis results, so the design alone cannot establish the direction or size of any condition differences.

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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Shown below are peak drug effects from each of the 3 maintenance periods (Placebo, Pioglitazone (PIO) 15, and PIO 45)

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: Recreational prescription opioid users.

6. Primary Endpoint

The registry lists the primary outcome as Subjective Ratings of "Good" Drug Effect, measured over Measured during the lab session conducted at the end of each maintenance period.

The primary endpoint is titled “Subjective Ratings of ‘Good’ Drug Effect.” It measures participants’ reported experience of oxycodone during laboratory assessment after each maintenance period. Ratings were collected on a visual analog scale described as 0-100 mm, where 0 means “Not at all” and 100 means “Extremely.” The registry identifies the outcome as a mean of a continuous measure and specifies that the reported value represents peak drug effects from the placebo, pioglitazone 15 mg, and pioglitazone 45 mg periods. The measure’s dispersion is identified as standard deviation.

As a general measurement rationale, a self-report scale can capture a participant’s subjective appraisal of a drug effect that may not be represented by a physiological measurement. Asking about a good effect is relevant to a study of abuse liability because it focuses on a positively experienced subjective response. That rationale does not make the rating a direct measure of misuse, dependence, or future behavior, and it does not establish that a higher or lower rating predicts a clinical outcome.

For interpretation, the scale anchors and timing matter: the rating is a peak response during a laboratory session after a maintenance period, not a measure of longer-term behavior. The registry record does not report the observed means or standard deviations for the conditions, so the magnitude and precision of the ratings cannot be assessed from the record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a continuous rating summarized as a mean, with standard deviation as the measure of dispersion. General statistical interpretation separates the average response from its variability. A mean indicates the center of the observed ratings; a standard deviation describes participant-to-participant spread. Neither is a direct measure of how certain a comparison is. Precision for a contrast is usually communicated with a confidence interval or another uncertainty measure, but no such result is reported for the primary outcome in the registry record.

What does a crossover design imply?

In general, a crossover study measures participants under more than one condition, so each person may contribute data to multiple condition summaries. This can be useful because stable characteristics of a participant are shared across their measurements. A paired analysis can use the within-person changes rather than treating all observations as independent. However, the registry record does not state which statistical method was used, whether comparisons were paired, or whether all participants contributed measurements under each condition. The design description by itself does not establish the analysis method.

Condition order is important in crossover studies. Ratings can be associated with period or sequence, and an earlier condition can potentially influence a later assessment. General crossover analyses may account for period effects or evaluate whether carryover is plausible. The registry record does not report the order of the placebo and pioglitazone periods, a washout procedure, or a model addressing period and carryover. With non-randomized allocation, the record’s caution against treating the conditions as like-for-like controls is especially relevant. It is not possible to infer that the order or other sources of systematic differences were balanced.

How should the scale be read?

The scale runs from 0-100 mm, with anchors of 0 for “Not at all” and 100 for “Extremely.” The recorded endpoint is peak good drug effect during the laboratory session at the end of each maintenance period. In general, a mean on this scale summarizes average reported intensity, but the numerical value should be interpreted in light of the anchors, variation among participants, and the conditions under which ratings were collected. The record does not report the observed means or standard deviations, so no scale value or comparison can be interpreted.

What do the planning assumptions mean?

The stated planning framework uses a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It describes an effect to detect as a stated fraction of the observed effect. These are assumptions for a planning illustration, not evidence about what the study was powered to detect or the precision actually achieved. The record does not report the study’s own sample-size justification. Any sample-size illustration should be understood as planning rather than observed power; it cannot show that an effect was or was not present.

General power calculations depend on assumptions about the target effect, variability, significance threshold, allocation, and analysis. If the target effect is defined relative to an observed effect, the illustration is conditional on that observed estimate and does not independently establish the size of a clinically important effect. For a crossover study, the relationship between repeated measurements also matters to precision. The record does not report the correlation between repeated ratings or enough detail to assess whether the planning assumptions match the analysis structure.

What can be said about statistical testing?

A hypothesis test evaluates the compatibility of data with a specified null model under stated assumptions. A p-value, if reported, would not quantify the size or importance of a condition difference, and it would not substitute for an estimate with an interval. Here, the registry lists zero analyses and gives no test statistics, p-values, contrasts, or confidence intervals. Thus there is no reported inferential result to interpret. It would be inappropriate to infer the outcome from the design, enrollment, or safety counts.

Because the available record does not report the model, handling of repeated measures, or uncertainty estimates, readers cannot determine how dependence among measurements was represented or whether adjustment was made for any other factors. Such details are important in general because treating repeated observations as independent can misstate uncertainty. This is a methodological consideration, not a claim that the study used an inappropriate method.

10. Multiplicity, Missing Data and Analysis Populations

The registry describes a primary subjective rating and lists analgesic responses using the cold pressor test as a secondary outcome. The study summary also identifies cognitive and physiological responses as secondary aims. Testing several outcomes or comparing multiple maintenance conditions creates a multiplicity issue: in general, the more comparisons considered, the greater the chance that at least one result appears notable by chance when all null hypotheses are true. This concern is ordinarily addressed by defining a testing hierarchy, adjusting significance thresholds, or interpreting secondary findings as exploratory. The registry record does not report a multiplicity plan or adjustment.

The record lists zero analyses and does not provide outcome estimates or tests, so there are no reported comparisons on which to assess multiplicity adjustment. It does not state whether the primary outcome was analyzed as one overall test or as multiple pairwise comparisons among placebo, 15 mg, and 45 mg conditions. The statistical plan and prespecified analysis details are not reported in the registry record.

Missing-data handling is also not reported. The enrollment count is 32, but that does not establish how many participants completed each maintenance period or contributed endpoint measurements. The record does not report missing ratings, reasons for missingness, imputation, or sensitivity analyses. In general, missingness can affect both the estimate and its uncertainty, especially when the chance of a missing measure is related to the participant’s response or condition. No conclusion about completeness can be drawn from the enrollment figure alone.

The analysis population is not reported in the registry record. It is therefore unclear whether analyses were intended to include all enrolled participants, only those completing all periods, or another defined group. These reporting gaps limit assessment of the strength and reproducibility of any analysis, and they cannot be resolved from the design description alone.

11. 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 0% reporting threshold.

The registry reports that all participants were included in the group described as at risk for serious adverse events: 32 at risk and 0 affected. For other adverse events, it also reports 32 at risk and 0 affected. The record lists no serious adverse event terms. These are the posted event counts for the group, not a complete characterization of every possible safety outcome.

The death count is not reported in the registry record. A blank or null count should not be read as a reported zero. Similarly, zero affected in the recorded categories means that no events were entered for those categories in this record; it does not prove that an event was impossible or that there was no safety risk. The record does not provide details about surveillance, event definitions, duration of observation, or condition-specific exposure for these counts.

Because the safety figures are reported for all participants together, they do not show whether events differed across placebo and pioglitazone maintenance periods. These data also do not answer the primary question about subjective ratings of oxycodone’s good drug effect. Safety counts and efficacy-related outcome measurements address different questions and should be interpreted separately.

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

The registry record describes a laboratory study of subjective oxycodone responses after placebo or pioglitazone maintenance. It identifies the primary measure, its scale, the assessment timing, and the broad crossover design. It does not report numerical primary outcome results. Therefore, the posted record does not establish whether the average good drug effect rating was higher, lower, or similar across the maintenance conditions.

The missing estimates also mean that the size and precision of any possible difference cannot be judged. Without condition means, variability, contrasts, or confidence intervals, there is no basis for saying whether the data are compatible with a small difference, a large difference, or substantial uncertainty. No statistical test result is reported, so statistical significance cannot be assessed either.

Even if numerical differences were available, a subjective rating in a controlled laboratory session would address a limited outcome. As a general distinction, a report of perceived good drug effect is not itself a measure of long-term misuse, dependence, treatment success, or behavior outside the laboratory. The registry does not report those outcomes as the primary endpoint. Nor does the design description alone establish a causal effect: allocation was non-randomized, and the record cautions that the conditions are not a like-for-like control comparison.

The safety record lists zero serious and zero other adverse events among 32 participants at risk, while the death count is not reported. These figures describe the registry’s event reporting and do not supply the absent primary outcome findings. The appropriate interpretation is therefore limited: the record documents the planned question and some design and safety information, but it does not provide the numerical evidence needed to characterize the primary outcome result.

13. Why This Trial Matters Statistically

This study illustrates how a clinical question and an outcome definition can be reported without the numerical results needed to answer that question. The endpoint is clearly framed as a peak subjective rating, with scale anchors and an assessment time. That makes the intended measurement understandable, but an endpoint description is not a result. Without condition-specific estimates and uncertainty, readers cannot assess the size or precision of a difference.

The crossover design also highlights why design labels and analysis details should be read together. Repeated measures can make within-participant comparisons informative in general, but condition order, period effects, carryover, and missing measurements can matter. The registry identifies a crossover model while also describing non-randomized allocation and cautioning against a like-for-like comparison. It does not report the sequence or statistical model, leaving important aspects of the comparison unclear.

The record also makes clear that statistical interpretation requires more than an enrollment count. Sample-size planning depends on assumptions, and an illustration based on an observed effect is not observed power. Likewise, a standard deviation would describe spread, whereas a confidence interval would help convey uncertainty in a contrast. Neither the primary estimates nor the comparison uncertainty are reported.

Finally, multiplicity, missing data, and the analysis population affect how findings should be evaluated, yet these details are not reported in the registry record. The case therefore demonstrates a central principle of biostatistical reading: a trial’s design and measurement framework can be described, but conclusions about an outcome require transparent results and enough analysis detail to judge their reliability.

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.

Several limitations are specific to what the registry record reports. Allocation is identified as non-randomized, and the record explicitly warns that the conditions are not a like-for-like control comparison. Consequently, any comparison could be influenced by differences associated with allocation or assessment order, in addition to the maintenance condition. The record does not describe how conditions were sequenced or whether order was accounted for analytically.

The crossover model makes period and carryover details relevant, but the record does not report washout procedures, condition sequence, or a statistical method for repeated measures. Masking is described as single, while the identity of the masked party is not reported. These omissions prevent a detailed assessment of how expectations or time-related effects may have influenced subjective ratings.

The most direct limitation is that numerical primary results are not reported. Means, standard deviations, contrasts, confidence intervals, and p-values are absent, and the registry lists zero analyses. Without those results, the primary question cannot be answered from the posted record. The analysis population and handling of incomplete measurements are also not reported; enrollment of 32 does not establish how many participants contributed to each condition’s endpoint.

The registry does not report a multiplicity plan, a detailed statistical analysis plan, or the study’s own sample-size justification. Its general planning assumptions do not resolve these gaps. The record also does not provide detailed participant characteristics, which limits assessment of how broadly the study population represents other groups. These are reporting limitations; they do not establish that the underlying study lacked procedures or analyses that were not entered in the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Effects of Pioglitazone, a PPARgamma Receptor Agonist, on the Abuse Liability of Oxycodone — NCT01395784.
• Registry record last updated 2016-02-23; status last verified 2013-11.
• Results first posted 2016-02-23.
• 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 describes a completed phase 2, single-masked, non-randomized crossover study with enrollment of 32. It examined peak subjective ratings of oxycodone’s good drug effect after placebo, pioglitazone 15 mg, and pioglitazone 45 mg maintenance periods, each described as lasting 2-3 weeks. The primary measure used a 0-100 mm visual analog scale. Analgesic responses using the cold pressor test are listed as a secondary outcome, alongside broader stated aims concerning cognitive and physiological effects.

The record reports zero serious adverse events and zero other adverse events among 32 participants at risk; the death count is not reported. It lists zero analyses and does not report numerical primary outcome results, uncertainty estimates, or the analysis population. As a result, the posted registry information defines the research question and gives selected design details, but does not establish the direction, magnitude, or precision of the primary outcome findings.