Vaporized THC at higher doses helped rats unlearn aversive memories associated with opiate withdrawal, while injected THC at a moderate dose actually prolonged those memories fourfold.
Read this if you are interested in the neuroscience of addiction and how cannabis might interact with withdrawal and recovery.
Injected THC prolonged aversive withdrawal memories 4x at moderate dose
What the researchers found
Researchers tested whether THC could help rats extinguish conditioned place aversion, a learned avoidance behavior triggered by memories of opiate withdrawal. They compared vaporized and injected THC at multiple doses.
Vaporized THC at 5mg and 10mg facilitated extinction of the aversive memory, meaning rats more quickly stopped avoiding the location they associated with withdrawal. However, the lowest vaporized dose (1mg) did not help.
Injected THC showed the opposite pattern: the middle dose (1.0 mg/kg) prolonged the aversive memory fourfold compared to vehicle, while the lowest and highest injected doses had no effect. This suggests both dose and route of administration critically determine whether THC helps or hinders extinction of withdrawal-related memories.
Why it matters
Aversive memories associated with drug withdrawal drive relapse by creating powerful avoidance and craving. If THC can facilitate extinction of these memories, it could have therapeutic applications in addiction treatment, but the route and dose matter enormously.
The numbers in context
Vaporized 5mg and 10mg THC facilitated extinction; 1mg did not; injected 1.0 mg/kg prolonged aversion fourfold; 20-28 extinction trials per group
How the study worked
Rats were conditioned to associate a floor cue with naloxone-precipitated morphine withdrawal. During 20-28 extinction trials, they received either vaporized THC (1, 5, or 10mg) or injected THC (0.5, 1.0, or 1.5 mg/kg) before each trial.
What this study cannot tell us
Animal study that may not translate directly to human addiction. The conditioned place aversion model is a simplified version of human withdrawal memories. Dose equivalency between routes is approximate.
How to read the evidence
Controlled animal study with clear dose-response data, but translation to human addiction treatment is uncertain.
When this study was published
Published in 2015. Research on cannabinoids in addiction treatment has continued to evolve.
The bigger picture
The finding that the same drug can either help or hinder memory extinction depending on how it is delivered has broad implications for therapeutic use of cannabinoids. It also highlights that vaporized cannabis may have fundamentally different pharmacological effects than other routes.
Questions still open
- Could vaporized THC enhance exposure therapy for addiction in humans? Why does route of administration so dramatically alter the effect? Would CBD or other cannabinoids show similar route-dependent effects on extinction learning?
Common questions
Could THC help with opiate addiction?
Why did the route of delivery matter so much?
Read the original research
Comparative effects of pulmonary and parenteral Δ⁹-tetrahydrocannabinol exposure on extinction of opiate-induced conditioned aversion in rats.
Psychopharmacology, 232(9), 1655-65
Citation
Manwell, Laurie A; Mallet, Paul E. (2015). Comparative effects of pulmonary and parenteral Δ⁹-tetrahydrocannabinol exposure on extinction of opiate-induced conditioned aversion in rats.. Psychopharmacology, 232(9), 1655-65. https://doi.org/10.1007/s00213-014-3798-5
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