Rats Built Tolerance to THC but Didn't Show Withdrawal When It Stopped

Male and female Sprague-Dawley rats received THC (3 mg/kg, subcutaneous) or vehicle twice daily for 7 days. Tolerance assessed on day 8 by comparing THC's effects in pre-treated vs. naive rats. Spontaneous withdrawal monitored for 5 days after final dose using voluntary home cage wheel running as the primary outcome measure.

Cannabis withdrawal in humans is well-documented (RTHC-00037, RTHC-00004), but animal models have struggled to replicate it. This study used a dose that clearly produced tolerance — proving the brain adapted to THC — yet found no withdrawal when THC stopped. This disconnect between human and animal findings raises important questions about what drives cannabis withdrawal: is it purely pharmacological, or do psychological and environmental factors play a larger role in humans?

Previous animal studies using much higher THC doses reported only mild withdrawal symptoms. This study, using a moderate dose, found none — even with a more sensitive measurement tool. The human withdrawal literature tells a different story: clearly documented symptoms including sleep disruption (RTHC-00037, RTHC-00012), irritability, and appetite changes. This species difference could mean that human cannabis withdrawal involves learned associations, stress responses, or cognitive factors that rats don't experience, or that the dose and duration in animal models need to be much longer to produce dependence.

The 3 mg/kg dose, while producing clear tolerance, may not be high enough to induce dependence. Seven days of dosing is relatively short. Rats metabolize THC differently than humans. Wheel running, while sensitive, measures only motor activity — other withdrawal symptoms (sleep disruption, anxiety, appetite changes) weren't captured. The subcutaneous injection route doesn't match human inhalation.