How quickly does tolerance to cannabis develop, and does it reverse?

Tolerance to THC's psychoactive and some therapeutic effects develops rapidly with regular use. CB1 receptor downregulation and desensitization begin within days of daily use. PET imaging studies show CB1 receptor density decreases by 15–20% after 4 weeks of daily cannabis use. Tolerance to antiemetic effects appears to develop more slowly than tolerance to euphoria. Tolerance reverses with abstinence — CB1 receptor density returns to near-baseline within 4 weeks of cessation in most studies. Tolerance to CBD is less well-characterized; animal studies suggest minimal tolerance development, which may explain why Epidiolex maintains efficacy long-term. Cross-tolerance between THC and synthetic cannabinoids (dronabinol, nabilone) is well-documented.