Daily cannabis use may cause cannabis-induced hyperalgesia.

BACKGROUND AND OBJECTIVES: Public opinion about cannabis as a medical treatment is generally favorable. As many as 35% of primary care patients report medical use of cannabis, most commonly for pain treatment. We designed a way to test whether cannabis helps chronic pain.

METHODS: A retrospective cohort study was conducted to explore whether daily long-term cannabis use was associated with increased pain sensitivity using the cold pressor test (CPT) to measure pain tolerance. Patients who used cannabis every day were compared to patients who inhaled tobacco and control patients who never used tobacco or cannabis. The effect of cannabis use on CPT was assessed using a generalized linear model.

RESULTS: Patients using cannabis daily had a median CPT of 46 s, similar to those who did not use cannabis but who inhaled tobacco (median CPT 45 s). Patients who used both cannabis and tobacco had the lowest CPT (median 26 s). The control group had a median CPT of 105 s. Cannabis use was associated with a significantly decreased pain tolerance (χ²  = 8.0, p = .004). The effect of tobacco on CPT was only marginally significant (χ²  = 3.8, p = .052).

CONCLUSION AND SCIENTIFIC SIGNIFICANCE: This suggests a phenomenon similar to opioid-induced hyperalgesia; a drug that reduces pain short term, induces pain long term-opponent process. Daily cannabis use may make chronic pain worse over time by reducing pain tolerance. In terms of risk/benefit, daily cannabis users risk addiction without any long-term benefit for chronic pain.