Quote Originally Posted by Mark Bryan
Correction,cannabis is a cardiovascular DILATOR. Evidence of course can be the reddenin' of the eyes.
Believe it or not, it's actually both a constrictor and a dilator, Mark. THC and some of the other CBDs are great vaso-dilators after they begin to work their merry way through your neurochemistry. But for some reason, in the first hour or two after people smoke--and this may be from the pulmonary effects and smoking itself instead of an effect from the cannabinoids--there's some vaso-constriction that occurs in a large majority of people. My theory is that sativa strains are responsible for this construction/stimulation effect a lot more than the sedating indicas.

Anyway, this part of the response is adrenergic--as if you've had a shot of adrenalin. Your heart beats faster. You're stimulated and energized. Some people get the shakes or twitches. There's a diuretic effect that's caused by the increased heart rate, which moves blood through your kidneys at a faster rate, causing you to need to go to the bathroom more. This is when paranoia and panic attacks happen--during the adrenergic period. It's because of this adrenergic effect that weed-smoking puts people at a five-fold greater risk of heart attacks within the first two hours of smoking.

At the same time, some dilation action is occurring, too. The bloodshot eyes can happen right away. BP often goes down, especially after the initial adrenergic phase is over. Veins and muscles that at first constrict begin to relax noticeably. You being to chill and feel stoned instead of feeling jumpy and jittery. Again, I think much of these constriction vs relaxation effects have a lot to do with the specific sativa-vs-indica content because a pure indica probably doesn't cause nearly as much adrenergic effect even in the two-hour post-smoking period.

Anyway, this baffling, wonderful and also at times potentially dangerous substance is both a constrictor and a dilator.