The FAAH inhibitor URB597 reduced most morphine withdrawal symptoms in rats at multiple dose levels, supporting endocannabinoid modulation of opioid dependence.
Read this if you follow opioid addiction research and want to understand endocannabinoid-based treatment approaches.
Effective at 4 out of 5 dose levels tested
What the researchers found
Rats made dependent on morphine through 7 days of daily injections received URB597, a FAAH inhibitor that boosts anandamide levels, before naloxone-precipitated withdrawal. URB597 at doses of 0.1 to 1 mg/kg reduced most withdrawal symptoms including jumping, teeth chattering, paw tremor, wet dog shakes, face grooming, and weight loss.
Only the lowest dose tested (0.03 mg/kg) failed to produce significant effects. The broad dose-response range suggested robust endocannabinoid involvement in opioid withdrawal modulation.
The results demonstrated that endocannabinoids interact with the opioid system during withdrawal, and that boosting endocannabinoid tone through enzyme inhibition could be a therapeutic strategy for managing morphine addiction.
Why it matters
Opioid withdrawal is a primary driver of continued opioid use. Finding that boosting natural endocannabinoids reduces withdrawal opens a potential treatment path that avoids the psychoactive effects of directly using cannabinoid drugs.
The numbers in context
URB597 effective at 0.1, 0.3, 0.5, and 1 mg/kg. Ineffective at 0.03 mg/kg. 10 withdrawal symptoms measured over 30-minute observation period. 7-day morphine dependence protocol.
How the study worked
Morphine dependence was induced by 7 consecutive days of morphine injections in rats. URB597 (0.03, 0.1, 0.3, 0.5, 1 mg/kg) was administered before naloxone-precipitated withdrawal. Ten different withdrawal symptoms were recorded during 30 minutes after naloxone injection.
What this study cannot tell us
Rat model of opioid dependence. Naloxone-precipitated withdrawal is more abrupt than natural withdrawal. Only acute URB597 administration was tested. Long-term safety of FAAH inhibition was not assessed.
How to read the evidence
Animal study with dose-response data. Consistent with findings from other labs but no human data available.
When this study was published
Published in 2011. FAAH inhibitor development has continued, though clinical trials have faced setbacks including a serious safety incident with a different FAAH inhibitor (BIA 10-2474) in 2016.
The bigger picture
This study complemented RTHC-00512 (which tested both FAAH and MAGL inhibitors) and strengthened the case that endocannabinoid enzyme inhibitors could become tools for managing opioid withdrawal. The consistent findings across labs increased confidence in the approach.
Questions still open
- Would URB597 or similar FAAH inhibitors work in human opioid withdrawal? Could FAAH inhibitors be combined with standard withdrawal medications for better outcomes? What is the long-term safety profile?
Common questions
What is FAAH and why does blocking it help?
Is this the same as using cannabis for opioid withdrawal?
Read the original research
Behavioral effects of fatty acid amide hydrolase inhibition on morphine withdrawal symptoms.
Brain research bulletin, 86(1-2), 118-22
Citation
Shahidi, Siamak; Hasanein, Parisa. (2011). Behavioral effects of fatty acid amide hydrolase inhibition on morphine withdrawal symptoms.. Brain research bulletin, 86(1-2), 118-22. https://doi.org/10.1016/j.brainresbull.2011.06.019
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