Transient ischemic attack in heavy cannabis smokers--how 'safe' is it?

Drugs are lately considered high-risk factors for cerebrovascular disease. Three male patients (mean age 24.6 years) who were heavy cannabis smokers presented with transient ischemic attacks (TIA) shortly after cannabis abuse. The complete examination of all 3 consisted of: EEG, brain CT scan, brain MRI, cerebral vessel angiography (digital subtraction and magnetic resonance angiography); also a full cerebrospinal fluid, urine and blood analysis (immunological, biochemical and hormonal tests were included). Urine was further examined for drug metabolites. An extensive cardiological investigation was carried out. Small vessel leukoencephalopathy was revealed by the brain CT and MRI. EEG recordings of the first patient showed paroxysmal sharp waves with left hemispheric dominance. The other 2 patients had diffuse delta and theta activity in their EEG tracings. The urine analysis was positive for cannabis metabolites. There were no other abnormal findings in the rest of the meticulous and thorough study of all 3 patients, which leads to the conclusion that cannabis was the only risk factor responsible for the observed TIA, contradictory to other studies, which support that cannabis is a 'safe' drug. More research is required in order for this issue to be completely elucidated.