Can cannabis-lowered brain receptors come back in about 4 weeks?
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Can the brain's cannabinoid receptors come back after a break from cannabis?
In a PET study at the US National Institutes of Health (Hirvonen et al., Molecular Psychiatry, 2012), 30 men who used cannabis daily (about 10 joints a day for about 12 years) had about 20% fewer CB1 receptors in the cortex than 28 men who didn't. 14 of them stayed cannabis-free on a monitored unit and were scanned again after 26 days on average: receptors returned to normal levels in most regions. One region, the hippocampus, did not bounce back in that time.
Sources
Hirvonen J, Goodwin RS, Li CT, et al. Reversible and regionally selective downregulation of brain cannabinoid CB1 receptors in chronic daily cannabis smokers. Mol Psychiatry 2012;17(6):642-649. doi:10.1038/mp.2011.82
What the study says
- “we measured CB 1 receptors using PET and [18 F]FMPEP- d 2 in chronic daily cannabis smokers (N = 30 subjects) and in control subjects with minimal lifetime exposure to cannabis (N = 28 subjects).”
- “Participants smoked an average of 10 ± 6 joints or blunts per day (range 1–30) for 12 ± 7 years (range 4–37).”
- “BMI-adjusted V T was ~20% lower in neocortex and limbic cortex, but not in other brain regions (basal ganglia, midbrain, thalamus, pons, or cerebellum; Figures 1 and 2).”
- “we repeated PET measurements in 14 cannabis smokers after 26 ± 5 days of monitored abstinence (range 13–32 days).”
- “After ~4 weeks of continuously monitored abstinence from cannabis on a secure research unit, CB 1 receptor density returned to normal levels.”
Where it falls short
Small, men only, one study.
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