Hello! Thank you for asking on HCM! Your symptoms seem to be related to cardiac tachyarrhythmia, induced from marijuana. Marijuana smoking can lead to marked increase in heart rate, lesser increases in supine blood pressure and frequent occurrence of postural hypotension. The latest would explain the feeling of fainting. On the one hand, these effects seem to be dose dependent, but on the other hand, the frequent use over a relatively short period of time results in tolerance. This means that after smoking regularly for some time, your body gets used to marijuana effects and you don t experience such symptoms when smoking marijuana any more. But, I would recommend consulting with a GP for a careful physical examination, a resting ECG, a chest x ray and some blood lab tests (complete blood count, thyroid hormone levels, blood electrolytes, fasting glucose, etc), to rule out any possible underlying conditions. Meanwhile I would advise you to avoid smoking marijuana, because of these side effects on your cardio-vascular system and other side effects on different body organs. It can lead to tolerance (you need high doses to have the same effect) and addiction (you can t live without that). Hope to have been helpful! Best wishes, Dr. Iliri