Cannabis Side Effects And Drug Interactions: Everything You Need To Know

This article was originally published on The Cannigma, and appears here with permission.

There are over 140 different kinds of cannabinoids out there, and out of the few, we’ve begun to study we’ve already discovered a multitude of health benefits and treatment targets. Whether it’s helping cancer patients, or curbing inflammation and beyond, the therapeutic potential of this plant offers many medical patients a chance at a better, more pain-free life.

Despite its many medical benefits, patients should proceed with caution as cannabis does have side effects, and it can also interact with other drugs. While more conclusive research is ultimately needed before we can determine the full extent of the plant’s drug interactions, researchers have already identified several common ones.

These findings are presented below to help you make better choices regarding your healthcare options, but you should always consult with a doctor before initiating treatment. Elderly patients and those with chronic diseases such as kidney, heart, and liver conditions should use extreme caution.

Common Adverse Reactions of Cannabis

Much of the current research regarding negative adverse reactions of medical marijuana is inconclusive. A 2016 research paper summed up the known adverse effects of cannabis neatly:

Short-term Use

  • Impaired short term memory, making it difficult to learn and retain information
  • Impaired motor coordination, interfering with driving skills and increasing the risk of injuries
  • Altered judgment
  • In high doses, paranoia, and psychosis

Long-term Use

  • Potential dependence: less than 10% of users meet DSM criteria
  • Altered brain development
  • Cognitive impairment, with lower IQ among those who were frequent users during adolescence
  • Symptoms of chronic bronchitis
  • Increased risk of chronic psychosis disorders in persons with a predisposition to such disorders

Adverse Effects of THC

THC, Paranoia, and Psychosis

One of the more serious side effects to note with THC is its potential link to psychosis. Research notes that the link to psychosis is especially potent among people with a “preexisting genetic vulnerability and exacerbates the course of illness in patients with schizophrenia.” THC can also increase feelings of paranoia and reduce working memory capacity. Patients who have a history of psychosis are strongly discouraged from taking any potentially psychotropic substances.  

Cognitive Function and Brain Development

Researchers have noted that cannabis use in adolescence (prior to age 21) can result in impaired neural connectivity (fewer fibers) in several brain regions. Image studies conducted on users also reveal decreased volume in the hippocampus, the region of the brain responsible for the formation of new memories, as well as decreased activity in prefrontal regions. This decreased frontal activity can negatively affect areas related to executive function including working memory and the ability to process habits and routines. 


Researchers estimate that less than 10% of cannabis users meet the criteria for dependence according to DSM criteria (the Diagnostic and Statistical Manual of Mental Disorders). This figure increases to “about 1 in 6 among those who start using marijuana as teenagers and to 25 to 50% among those who smoke marijuana daily.”

Cannabinoid Hyperemesis Syndrome

A rare side effect of chronic use is cannabinoid hyperemesis syndrome (CHS), a condition that causes severe and repeated instances of vomiting. 

A recent study noted that the transient receptor potential vanilloid subtype 1 (TRPV1) —a receptor involved in gastric motility—“is centrally involved in the pathogenesis of CHS”. Researchers postulate chronic cannabis use decreases signaling of TRPV1, resulting in said gastric motility issues. 

Many CHS patients report relieving their symptoms through frequent hot baths or use of topical capsaicin …

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