Prescription Medication Interactions

Prescription Medications: Pharmacodynamics and Interaction Effects

This study will examine the effects of doses of opioid/placebo and doses of sedative/placebo, alone and in combination. The primary outcomes are related to pharmacodynamic measures (subjective ratings of drug liking and other abuse-related effects; physiological outcomes) to determine the interaction effects of these compounds.

Study Overview

• Status: Completed
• Conditions: Opioid Use; Sedative Use
• Intervention / Treatment: Drug: Opioid Agonist; Drug: Sedatives

Detailed Description

Gabapentin and oxycodone are commonly used in combination for the treatment of chronic pain. Gabapentin is now widely misused/abused with studies indicating that gabapentin abuse is especially common among individuals with opioid misuse. The nature of gabapentin's abuse-related effects have been described in case reports and online as sedative-like and opioid-like, with descriptive reports including sedation, euphoria, talkativeness and increased energy. Despite their widespread co-administration both for licit and illicit purposes, no controlled psychopharmacological studies to our knowledge have directly examined the effects of oxycodone (or another opioid agonist) and gabapentin in combination. This study's objective is to characterize the subjective effect profile of gabapentin, examine the interaction between gabapentin and oxycodone, and assess the acute analgesic response to gabapentin and oxycodone, alone and in combination, across a range of doses for each drug.

• Study Type: Interventional
• Enrollment (Actual): 11
• Phase: Phase 1

Contacts and Locations

Study Locations

• United States
  • Kentucky
    • Lexington, Kentucky, United States, 40508
      • Center on Drug and Alcohol Research

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 55 years (Adult)
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Healthy adults, ages 18-55
• Current non-medical use of opioids and sedatives

Exclusion Criteria:

• Physical dependence on opioids, alcohol, or benzodiazepines/sedatives/hypnotics
• Seeking treatment for drug use
• Significant medical problems

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: Double

Number of Arms

9

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Placebo Comparator: Placebo / Placebo; Participants will receive non-therapeutic experimental doses of gabapentin (600 and 1200 mg, p.o.), alone and in combination with oxycodone (20 and 40 mg, p.o.). The experimental sessions are designed to capture the time-action curves for the test drugs (Tmax for gabapentin ≈ 2.5 hr; oxycodone ≈ 1.5 hr). Therefore, oxycodone will be administered 1 hr after gabapentin to align peak responses.	Drug: Opioid Agonist; Abuse liability evaluation.; Drug: Sedatives; Abuse liability evaluation.
Experimental: Placebo / Oxycodone 20mg; Participants will receive non-therapeutic experimental doses of gabapentin (600 and 1200 mg, p.o.), alone and in combination with oxycodone (20 and 40 mg, p.o.). The experimental sessions are designed to capture the time-action curves for the test drugs (Tmax for gabapentin ≈ 2.5 hr; oxycodone ≈ 1.5 hr). Therefore, oxycodone will be administered 1 hr after gabapentin to align peak responses.	Drug: Opioid Agonist; Abuse liability evaluation.; Drug: Sedatives; Abuse liability evaluation.
Experimental: Placebo / Oxycodone 40mg; Participants will receive non-therapeutic experimental doses of gabapentin (600 and 1200 mg, p.o.), alone and in combination with oxycodone (20 and 40 mg, p.o.). The experimental sessions are designed to capture the time-action curves for the test drugs (Tmax for gabapentin ≈ 2.5 hr; oxycodone ≈ 1.5 hr). Therefore, oxycodone will be administered 1 hr after gabapentin to align peak responses.	Drug: Opioid Agonist; Abuse liability evaluation.; Drug: Sedatives; Abuse liability evaluation.
Experimental: Gabapentin 600mg / Placebo; Participants will receive non-therapeutic experimental doses of gabapentin (600 and 1200 mg, p.o.), alone and in combination with oxycodone (20 and 40 mg, p.o.). The experimental sessions are designed to capture the time-action curves for the test drugs (Tmax for gabapentin ≈ 2.5 hr; oxycodone ≈ 1.5 hr). Therefore, oxycodone will be administered 1 hr after gabapentin to align peak responses.	Drug: Opioid Agonist; Abuse liability evaluation.; Drug: Sedatives; Abuse liability evaluation.
Experimental: Gabapentin 1200mg / Placebo; Participants will receive non-therapeutic experimental doses of gabapentin (600 and 1200 mg, p.o.), alone and in combination with oxycodone (20 and 40 mg, p.o.). The experimental sessions are designed to capture the time-action curves for the test drugs (Tmax for gabapentin ≈ 2.5 hr; oxycodone ≈ 1.5 hr). Therefore, oxycodone will be administered 1 hr after gabapentin to align peak responses.	Drug: Opioid Agonist; Abuse liability evaluation.; Drug: Sedatives; Abuse liability evaluation.
Experimental: Gabapentin 600mg / Oxycodone 20mg; Participants will receive non-therapeutic experimental doses of gabapentin (600 and 1200 mg, p.o.), alone and in combination with oxycodone (20 and 40 mg, p.o.). The experimental sessions are designed to capture the time-action curves for the test drugs (Tmax for gabapentin ≈ 2.5 hr; oxycodone ≈ 1.5 hr). Therefore, oxycodone will be administered 1 hr after gabapentin to align peak responses.	Drug: Opioid Agonist; Abuse liability evaluation.; Drug: Sedatives; Abuse liability evaluation.
Experimental: Gabapentin 1200mg / Oxycodone 20mg; Participants will receive non-therapeutic experimental doses of gabapentin (600 and 1200 mg, p.o.), alone and in combination with oxycodone (20 and 40 mg, p.o.). The experimental sessions are designed to capture the time-action curves for the test drugs (Tmax for gabapentin ≈ 2.5 hr; oxycodone ≈ 1.5 hr). Therefore, oxycodone will be administered 1 hr after gabapentin to align peak responses.	Drug: Opioid Agonist; Abuse liability evaluation.; Drug: Sedatives; Abuse liability evaluation.
Experimental: Gabapentin 600mg / Oxycodone 40mg; Participants will receive non-therapeutic experimental doses of gabapentin (600 and 1200 mg, p.o.), alone and in combination with oxycodone (20 and 40 mg, p.o.). The experimental sessions are designed to capture the time-action curves for the test drugs (Tmax for gabapentin ≈ 2.5 hr; oxycodone ≈ 1.5 hr). Therefore, oxycodone will be administered 1 hr after gabapentin to align peak responses.	Drug: Opioid Agonist; Abuse liability evaluation.; Drug: Sedatives; Abuse liability evaluation.
Experimental: Gabapentin 1200mg / Oxycodone 40mg; Participants will receive non-therapeutic experimental doses of gabapentin (600 and 1200 mg, p.o.), alone and in combination with oxycodone (20 and 40 mg, p.o.). The experimental sessions are designed to capture the time-action curves for the test drugs (Tmax for gabapentin ≈ 2.5 hr; oxycodone ≈ 1.5 hr). Therefore, oxycodone will be administered 1 hr after gabapentin to align peak responses.	Drug: Opioid Agonist; Abuse liability evaluation.; Drug: Sedatives; Abuse liability evaluation.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Subject-Rated Outcome: Visual Analog Scale (VAS) Drug Liking	Participants rated their subjective drug liking on a standardized VAS scale (0 to 100). Raw data transformed to peak scores. Higher scores indicate greater drug effects.	This outcome was recorded prior to and in regular intervals after drug administration for the duration of the session (approx. 8 hours per session).

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Subject-Rated Outcome: Visual Analog Scale (VAS) Drug Effect	Participants rated their subjective drug effect on a standardized VAS scale (0 to 100). Raw data transformed to peak scores. Higher scores indicate greater drug effects.	This outcome was recorded prior to and in regular intervals after drug administration for the duration of the session (approx. 8 hours per session).
Change in Respiration Rate	Respiration rate (number of breaths per minute). Raw data transformed to trough scores. Lower scores indicate greater impairment.	Respiration rate was recorded prior to and in regular intervals after drug administration for the duration of the session (approx. 8 hours per session).
Change in End-tidal Carbon Dioxide (EtCO2)	EtCO2 collected via capnograph monitored throughout each session. Raw data transformed to peak scores. Higher scores indicate greater impairment.	EtCO2 recorded prior to and in regular intervals after drug administration for the duration of the session (approx. 8 hours per session).
Change in Oxygen Saturation	Oxygen saturation (measured as a percentage through pulse ox) monitored throughout each session. Raw data transformed to trough scores. Lower scores indicate greater impairment.	Oxygen saturation recorded prior to and in regular intervals after drug administration for the duration of the session (approx. 8 hours per session).

Collaborators and Investigators

• Sponsor: Sharon Walsh
• Collaborators: National Institute on Drug Abuse (NIDA)
• Investigators: Principal Investigator: Sharon L Walsh, Ph.D., University Of Kentucky

Study record dates

Study Major Dates

• Study Start (Actual): March 25, 2019
• Primary Completion (Actual): May 6, 2023
• Study Completion (Actual): May 6, 2023

Study Registration Dates

• First Submitted: March 17, 2020
• First Submitted That Met QC Criteria: March 17, 2020
• First Posted (Actual): March 19, 2020

Study Record Updates

• Last Update Posted (Estimated): October 20, 2025
• Last Update Submitted That Met QC Criteria: October 14, 2025
• Last Verified: October 1, 2025

More Information

Terms related to this study

• Keywords: opioid; sedative; opiate
• Additional Relevant MeSH Terms: Physiological Effects of Drugs; Peripheral Nervous System Agents; Central Nervous System Depressants; Sensory System Agents; Analgesics; Narcotics; Pharmacologic Actions; Chemical Actions and Uses; Therapeutic Uses; Central Nervous System Agents; Analgesics, Opioid; Hypnotics and Sedatives
• Other Study ID Numbers: 46591; R01DA016718 (U.S. NIH Grant/Contract)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: We have no plans to share individual participant data with other researchers.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No