An Opiate Blocker Also Blocked THC Effects in Rats, Suggesting Shared Brain Pathways | Research

The takeaway

An irreversible opiate antagonist inhibited THC-induced pain relief, body temperature reduction, tolerance, and physical dependence in rats, suggesting cannabis and opiates share some overlapping brain mechanisms.

Read this if you want to understand the scientific basis for the connection between cannabis and opioid systems in the brain.

An opiate blocker inhibited four distinct THC effects in rats

What the researchers found

Researchers administered chlornaltrexamine (beta-CNA), a long-acting irreversible opiate receptor blocker, to rats before giving them THC. The opiate blocker inhibited several key THC effects: pain relief (analgesia), body temperature reduction (hypothermia), the development of tolerance to hypothermia, and the development of physical dependence.

These results suggested that some of THC's effects in the brain are mediated through opioid-related mechanisms, meaning cannabis and opiates share common features in how they interact with the central nervous system.

Why it matters

This study provided early pharmacological evidence for cross-talk between the cannabinoid and opioid systems in the brain. This connection has since become a major area of research, with implications for pain management, addiction treatment, and understanding why cannabis and opioids can sometimes substitute for each other.

The numbers in context

Beta-CNA inhibited four measured THC effects: analgesia, hypothermia, hypothermia tolerance, and physical dependence.

How the study worked

Animal study in rats using chlornaltrexamine (beta-CNA), a selective irreversible opiate antagonist, administered before THC. Measured analgesia, hypothermia, hypothermia tolerance, and physical dependence.

What this study cannot tell us

Animal study in rats; results may not translate directly to humans. Chlornaltrexamine is not perfectly selective, so some effects could involve non-opioid mechanisms. The study did not identify which specific opioid receptor subtypes were involved.

How to read the evidence

An animal pharmacology study providing mechanistic insight. Valuable for understanding biological pathways but cannot be directly applied to human clinical use.

When this study was published

Published in 1981. The endocannabinoid system was not discovered until 1988-1992, so the full picture of cannabinoid-opioid interaction was not yet understood.

The bigger picture

The cannabinoid-opioid interaction documented here was foundational. Decades of subsequent research confirmed extensive overlap between these systems, leading to investigations of whether cannabis might reduce opioid requirements for pain management, a question with major public health implications during the opioid crisis.

Questions still open

Which specific opioid receptors mediate THC's effects? Does this cross-talk exist in humans at clinically relevant doses? Could this interaction be leveraged therapeutically to reduce opioid requirements?

Common questions

Does this mean cannabis works like an opiate?

Not exactly. It means some of THC's effects appear to involve opioid-related pathways in the brain, but cannabis and opiates are distinct drug classes with different primary mechanisms.

Is this relevant to using cannabis for pain?

Yes. The overlap between cannabinoid and opioid systems is now a major area of research, particularly regarding whether cannabis can reduce the amount of opioids needed for pain management.

Read the original research

Antagonism by chlornaltrexamine of some effects of delta 9-tetrahydrocannabinol in rats.

European journal of pharmacology, 70(2), 219-24

View on PubMed ↗

Citation

Tulunay, F C; Ayhan, I H; Portoghese, P S; Takemori, A E. (1981). Antagonism by chlornaltrexamine of some effects of delta 9-tetrahydrocannabinol in rats.. European journal of pharmacology, 70(2), 219-24.