Side Effects of Medical Cannabis

Safety Profile of Medical Cannabis

• Average effective oral dosing range of plant based cannabinoids is 0.05-25mg/kg/day. When starting medical cannabis, it is a good rule of thumb to “start low and go slow” when titrating the dose up. The lowest effective dose should be consumed.

• No deaths occurred in monkeys treated acutely with delta-9-tetrahydrocannabinol (THC) with up to 9,000mg/kg.

Acute fatal cases in humans have not been substantiated.

Myocardial infarction may be triggered by inhaled THC due to effects on circulation in individuals who are unable to tolerate orthostatic hypotension or tachycardia.

Safety and side effects of Medical Cannabis

Further study is needed, however medical cannabis use is generally considered safe. Different strains of cannabis have different amounts of THC and other cannabinoids and side effects may vary with the different strains.

The adverse effects of medical cannabis are within the range tolerated for other medications. A 2008 review found that in 23 randomized controlled trials there was no higher incidence of serious adverse events following medical cannabis use compared with control, while non-serious adverse events were significantly higher in the cannabinoid groups. Dizziness was the most common non-serious adverse effect.

Some side effects of medical cannabis include, but are not limited to:

  • Euphoria, altered consciousness
  • Acute panic or paranoid reaction
  • Altered motivation
  • Orthostatic hypotension
  • Headache
  • Dry mouth (xerostomia)
  • Dry eyes
  • Lightheadedness
  • Dizziness
  • Drowsiness
  • Fatigue
  • Nausea
  • Paranoid thinking
  • A disconnected state (dissociation)
  • Increased appetite
  • Coughs
  • Breathing problems, for people who smoke cannabis
  • Impaired attention, memory, and psychomotor performance
  • Increased heart rate (tachycardia)
  • Increased risk of heart attack or stroke
  • Withdrawal symptoms

Don’t drive or operate machinery when using cannabis.

Patients should consider discontinuing medical cannabis if it is not beneficial or if they are experiencing adverse effects.

Cannabis-naïve patients demonstrate more frequent adverse effects, while regular users experience less psychotomimetic, perceptual altering, and amnestic effects. THC can broaden its own therapeutic window over time due to heterogeneous tolerance-building to various effects, with therapeutic effects more resistant to tolerance development than side effects.

The adverse effects of medical cannabis cannot and should not be equated with the effects of illicit cannabis use or cannabis abuse.

While smoking is not the preferred delivery method for medical use, even long-term heavy cannabis smokers have no increased incidence of lung cancer, although they can suffer other pulmonary symptoms suggestive of obstructive lung disease.

If you have a mental health condition, use cannabis with caution. Cannabis use might worsen manic symptoms in people who have bipolar disorder. If used frequently, cannabis might increase the risk of depression. Cannabis use also might worsen depression symptoms. Research suggests that cannabis use increases the risk of psychosis in people who have schizophrenia.

Caution should be exercised when considering medical cannabis for individuals under the age of 25 years because the brain continues to develop until this age, and the potential for cannabis to have a lasting impact on cognitive performance is unknown.

Cannabis has a central nervous system (CNS) depressant effect. As a result, cannabis use in combination with anesthesia or other drugs used during or after surgery might cause an additive effect. Don’t use cannabis two weeks before planned surgery.

Pregnancy, Breast Feeding, and Medical Cannabis

Medical cannabis should not be used during pregnancy.  When cannabis is smoked or eaten, the chemicals reach the fetus by crossing the placenta. Research is limited on the harms of cannabis use during pregnancy. There are possible risks of cannabis use, including babies that are smaller at birth and stillbirth. Using cannabis also can be harmful to a pregnant woman’s health (see above for the list of side effects). The American College of Obstetricians and Gynecologists recommends that pregnant women not use cannabis.

It is recommended that you stop using cannabis before trying to get pregnant. The effects of cannabis on the fetus may occur even during the first trimester.

Researchers are still learning about the effects of cannabis during pregnancy. However, experts agree on the following:

  • Cannabis exposure may disrupt normal brain development of a fetus.
  • Babies whose mothers used cannabis during pregnancy may be smaller at birth.
  • Research suggests an increased risk of stillbirth. It is not known if this is only because of cannabis use or due to use of other substances, such as cigarettes.
  • Some studies suggest that using both cannabis and cigarettes during pregnancy can increase the risk of preterm birth.

Little is known about the effects of cannabis on breastfeeding babies. Because it is not clear how a baby may be affected by a mother’s cannabis use, the American College of Obstetricians and Gynecologists recommends that women who are breastfeeding not use cannabis.

If you live in a place with a medical cannabis program please have an honest conversation with your Physician to see if medical cannabis is a good fit for you. If you live in Missouri and you don’t have a Primary Care Physician, you can come see my wife, Dr. Strong in St. Louis. Dr. Strong will be providing Medical Marijuana Physician Certificates starting in June 2019.


Russo, Ethan B., Alice P. Mead, and Dustin Sulak. “Current Status and Future of Cannabis Research.” The Clinical Researcher 29:2 (2015): 58-64.

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