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

The takeaway

Male and female rats developed clear tolerance to THC's effects after seven days of dosing, but when THC was abruptly stopped, no spontaneous withdrawal symptoms were detected — even using a sensitive behavioral measure.

Addiction researchers studying cannabis dependence mechanisms, neuroscientists modeling withdrawal in animals, anyone curious about why cannabis withdrawal differs from other drugs.

What the researchers found

Researchers injected male and female rats with THC (3 mg/kg, twice daily) or vehicle for seven days, then abruptly stopped and monitored for withdrawal symptoms over five days using voluntary home cage wheel running — chosen as a sensitive, objective, and continuous measure.

On day 1, THC profoundly decreased wheel running in both sexes compared to vehicle-treated rats — confirming the drug's acute sedating effects. By day 8, rats that had received seven days of THC showed significantly less suppression of wheel running from a THC injection than THC-naive rats, demonstrating clear tolerance development. There was no sex difference in the magnitude of tolerance.

However, when THC was stopped after day 8, no measurable spontaneous withdrawal was detected in either sex. Wheel running returned to baseline without the rebound disruption that would indicate withdrawal. This was notable because the study specifically chose wheel running as a more sensitive withdrawal measure than the behavioral checklists used in earlier studies, which had also found minimal spontaneous withdrawal from THC.

Why it matters

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?

The numbers in context

THC dose: 3 mg/kg twice daily for 7 days. Clear tolerance demonstrated on day 8. No spontaneous withdrawal detected over 5 days of monitoring. No sex difference in tolerance development. Wheel running used as primary behavioral measure.

How the study worked

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.

Who was studied

Male and female Sprague-Dawley rats were used in the study.

What this study cannot tell us

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.

How to read the evidence

Controlled animal experiment — rigorous for demonstrating tolerance and measuring withdrawal in rats, but the human-animal translation gap limits direct clinical applicability.

When this study was published

Published in 2026, contributing to the ongoing debate about how well animal models capture human cannabis dependence.

The bigger picture

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.

Replication

Not stated in abstract.

Funding

Not reported in abstract.

Conflicts of interest

Not reported in abstract.

Questions still open

Would longer dosing periods or higher doses eventually produce spontaneous withdrawal in rats? Are there other behavioral measures that might detect subtler withdrawal effects? Does the human-animal disconnect in cannabis withdrawal point to a fundamentally different withdrawal mechanism than other drugs of abuse?

Read the original research

Tolerance but No Spontaneous Withdrawal Following Repeated THC Injections in Male and Female Rats.

Cannabis and cannabinoid research, 11(1), 68-77

Cannabis and Cannabinoid Research is a peer-reviewed journal focusing on cannabis science and its applications.

View on PubMed ↗Publisher’s paper ↗

Citation

Hickey, Christa M; Poling, Casey; Grimes, Wyatt; Calvert, Alexa R; Morgan, Michael M. (2026). Tolerance but No Spontaneous Withdrawal Following Repeated THC Injections in Male and Female Rats.. Cannabis and cannabinoid research, 11(1), 68-77. https://doi.org/10.1177/25785125251404395