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Understanding the Side Effects of Medical Cannabis

There is only one thing that all medications and that is side effects. Even seemingly harmless drugs can have unintended consequences, such as Tylenol rarely causing liver failure.  Understanding the side effects of a medication are crucial to safe prescription practices and use. In this respect, cannabis is no different than any other prescription medication. Fortunately, the potential side effects of cannabis are well-known and tend to be quite mild. I will briefly review the known side effects of cannabis and how to ensure safe usage.

Common Side Effects of Cannabis

Although not potentially fatal, there are side effects that are important to be aware of. Through numerous studies of cannabis for various purposes, the most common side effects are dizziness, fatigue, dry mouth or eyes, decreased coordination, euphoria, increased appetite, and confusion. Out of these, the side effects that patients tend to be bothered most by are the fatigue and dry mouth/eyes. For patients new to cannabis therapy, side effects are most likely to occur during therapy initiation and when doses and/or formulations are adjusted. This is because the body is seeing a new chemical for the first time or in a different dosage than previously. For many patients, these side effects subside over time and some resolve completely. When starting cannabis therapy, it may help ease any side effect burden if therapy is started during a time when other responsibilities are lessened (ex: if you work during the week, try starting therapy on Friday night or over the weekend to give yourself a chance to adjust).

Rare Side Effects of Cannabis

It is also important to be aware of the rarer side effects, in order to prevent alarm in case they happen to you. Cannabinoid hyperemesis syndrome results in uncontrollable nausea and vomiting. Although the disease isn’t dangerous and does not progress beyond these symptoms, nausea, and vomiting are obviously never experiences that one hopes for in life. Fortunately, the symptoms typically last only a few hours, or less, before resolving spontaneously. And for faster resolution, exposure to heat (ex: hot shower, capsaicin cream) is known to improve the symptoms quite quickly for most people. Also, very rarely at high doses marijuana can cause hallucinations, although this shouldn’t affect anyone using medical cannabis if used properly. If you experience hallucinations, stay calm as they too will likely resolve on their own as the cannabis wears off. You should then contact your doctor or dispensary, as your dosage is likely too high or you may be using your cannabis-based products incorrectly.

Cannabis Lacks the Potential for Fatal Overdose

The most advantageous aspect of medical cannabis, whether it is used for chronic pains or for any other reason, is the lack of overdose potential, an unfortunate side effect of opiates like Percocet or Oxycontin. At high enough doses, opiates decrease function in the brainstem, the part of the brain responsible for necessary functions of life such as breathing. The reason cannabis cannot cause a fatal overdose is because the brainstem simply does not have enough cannabinoid receptors to cause the same effect as opiates. To date, there are no known cases of fatal cannabis overdose in adolescents or adults. The inability to lead to a fatal overdose is incredibly important to the success of cannabis as a potential replacement for other medications (i.e. opiates) for pain control.

Activities to Avoid

Much like any other substance, legal or illegal, that can cause fatigue and decrease coordination, it is important to stay safe when using cannabis for medical purposes. As mentioned before, cannabis can alter perception, coordination, and reaction times, much in the same way that alcohol can. In this regard, safe cannabis use can be considered in the same manner as safe alcohol use. There is substantial evidence of an association between cannabis use and increased risk of motor vehicle crashes (up to 30% increased risk). For reasons mentioned above, activities that require significant coordination and other skills impacted by cannabis should be avoided,   driving, skiing, and hunting (to name a few). It is important to consider safety first, especially when starting therapy or changing doses.

Take Home Message

The side effect profile for cannabis is really quite manageable when used safely. It is important for patients routinely follow up with their medical providers and discuss any side effects with their medical providers, as well as with the dispensary staff. This will help patients to obtain optimal benefits and avoid unwanted side effects.


Campbell FA, Tramer MR, Carroll D, Reynolds DJM, Moore RA, McQuay HJ. Are cannabinoids an effective and safe treatment option in the management of pain? A qualitative systemic review. BMJ. 2001. 323: 1-5.

By |2019-04-18T19:56:33+00:00March 7th, 2019|Editorials, Marijuana|0 Comments

About the Author:

Dr. Bressman attended Swarthmore College, where he received a bachelors degree with a focus on biology, before attending the NYU School of Medicine, currently ranked as the #3 medical school by the US News Rankings. He is currently a resident in Internal Medicine at Montefiore Medical Center in the Bronx, NY. Dr. Bressman has participated in both basic science research, as well as clinical research, with multiple publications and awards. Most recently he was named the winner of the Trainee Award at the national conference for Society of Hospitalist Medicine for a rare case involving licorice toxicity. When not hard at work, Dr. Bressman can usually be found on the golf course or cooking at home.

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