When one thinks of hallucinogenic drugs, cannabis does not normally cross the mind first. Often seen as a relaxing drug, many patients even use it to ease anxiety.
However, emergency service workers have seen an increase in recent years in the hospital visits from patients hallucinating from cannabis, especially in the wake of recreational legalization across North America.
Many cannabis clinics across Canada and the US screen patients before assessing them for cannabis therapy. If a patient has a family history of psychosis, or if the patient themselves have had issues with schizophrenia and paranoia, they would usually be denied a prescription by a physician.
Having worked in a cannabis clinic for over two years, I have seen some cases, though uncommon, where patients experienced anxiety and sometimes did hallucinate due to ingesting too much tetrahydrocannabinol (THC), the psychoactive part of cannabis. Cannabidiol (CBD), the non-psychoactive part of the cannabis plant, does not seem to cause hallucinogenic reactions in patients. In fact, it may be used to counter the amount of THC in a strain.
Some people mistakenly believe that edibles are more potent and therefore are more likely to cause hallucinogenic reactions. However, this is simply untrue. The answer more likely is due to the fact that people ingest more edibles than they do when they inhale the substance. Edibles also take longer to manifest in the body, so symptoms may not be felt for hours after consumptions. This propels people to eat more in the meantime.
There is also a possibility that illegal cannabis could be laced with hallucinogens. Some agents like salvia, or K2, or spice, when bought in an illegal manner, may be laced with hallucinogens that can impact users.
Several studies have linked marijuana use to increased risk for psychiatric disorders, including psychosis in schizophrenia, depression, anxiety, and substance use disorders, but whether and to what extent it actually causes these conditions is not always easy to determine. Studies are ongoing to understand the effects.