Should you be worried if you lose consciousness after smoking marijuana?

"My niece has fainted right 3 times in the last year after smoking marijuana."

It is hard to know for sure what is behind her fainting spells, but marijuana can have some properties that could contribute to feeling lightheaded or faint. Side effects of marijuana are associated with the dose consumed, i.e. how "strong" it is, or how much THC is in it, as well as how it is consumed. The sudden onset of a smoked product would be very different than the effect of a milder product that is swallowed for instance, so different products and different routes of administration can definitely have different effects. Marijuana, particularly smoked marijuana which is predominantly THC, can lead to temporary changes in heart rate and blood pressure. Sometimes the heart can seem to "race" or go faster, and blood pressure can go down, particularly when first standing up. For a person who is dehydrated for instance, or with low or borderline blood pressure, this could theoretically lead to fainting as you described. Of course it would be very difficult to know for sure what happened specifically those 3 times, but it is something that she would definitely want to look into so it can be prevented from happening again. Fainting spells in young people aren’t usually due to something dangerous, but depending on your niece’s age, health level, heart health, etc it is hard to say what the cause is, so the safest approach would be to see her doctor and get checked out.


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