MD, PhD, MAE, FMedSci, FRSB, FRCP, FRCPEd.

Cannabis use is a frequently-discussed subject, not just in the realm of so-called alternative medicine (SCAM). In general, SCAM advocates view it as an herbal medicine and recommend it for all sorts of conditions. They also often downplay the risks associated with cannabis use. Yet, these risks might be substantial.

Cannabis potency, defined as the concentration of Δ9-tetrahydrocannabinol (THC), has increased internationally, which could increase the risk of adverse health outcomes for cannabis users. The first systematic review of the association of cannabis potency with mental health and addiction was recently published in ‘The Lancet Psychiatry’.

The authors searched Embase, PsycINFO, and MEDLINE (from database inception to Jan 14, 2021). Included studies were observational studies of human participants comparing the association of high-potency cannabis (products with a higher concentration of THC) and low-potency cannabis (products with a lower concentration of THC), as defined by the studies included, with depression, anxiety, psychosis, or cannabis use disorder (CUD).

Of 4171 articles screened, 20 met the eligibility criteria:

  • eight studies focused on psychosis,
  • eight on anxiety,
  • seven on depression,
  • and six on CUD.

Overall, higher potency cannabis, relative to lower potency cannabis, was associated with an increased risk of psychosis and CUD. Evidence varied for depression and anxiety. The association of cannabis potency with CUD and psychosis highlights its relevance in healthcare settings, and for public health guidelines and policies on cannabis sales.

The authors concluded that standardisation of exposure measures and longitudinal designs are needed to strengthen the evidence of this association.

The fact that cannabis use increases the risk of psychosis has long been general knowledge. The notion that the risk increases with increased potency of cannabis seems entirely logical and is further supported by this systematic review. Perhaps it is time to educate the public and make cannabis users more aware of these risks, and perhaps it is time that SCAM proponents negate the harm cannabis can do.

3 Responses to High potency cannabis is associated with an increased risk of psychosis

  • This one is so tough Edzard, with so much anecdotal junk on social media and so much hype from vested interests. So far as I can see there are only 3 medically valid justifications for use (not going to criticise those who use it safely, recreationally): nausea caused by chemotherapy, one specific type of seizure, and palliatively for psychological comfort for chronic incurable conditions and at end of life if desired. Even then it appears cannabis can make nausea and seizures worse – there are still risks.

    My main interest is in non-malignant chronic pain without sufficient explanatory pathology. There are massive amounts of studies and anecdotes around cannabis for chronic pain, but a wide review of the literature shows no such thing. The biggest study to date, an Australian one, reported that some 70% of users said it helped their pain, but their actual pain scores were higher, and they reported reduced ability to cope, more distress, and no decrease in opioid or other pain medication.

    With some exceptions, medical cannabis appears to be a con.

  • Not to question the need for research, anecdotally anyone working in psychiatric services knows this! There is also the added problem that you have literally no guarantee what you are being sold (why people trust drug dealers is as interesting as why they trust SCAM practitioners! 😉), and so much street cannabis is adulterated with synthetic psychoactive substances.

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