Perhaps this is a psychological issue? Personally, I find that mind set affects the consequences of weed a lot. If I am relaxed and feel the unity of everything(which is one of the lessons cannabis has taught me) during smoking, I find that it does not affect me much. In fact I cant take 5-6 heavy tokes, and still be pretty functional.
Before I knew this, too much weed would simply get my system overworked. There have been times that after 3 tokes from a bong, my heart beat would go real fast. I would experience epiphanies(one of which I learnt was the unity of all), my chakras would start firing up with energy(BTW I did not believe in chakras before I smoked week
) and I would end up just crashing on the bed really hard. Intensely vivid dreams would then follow.
I find that meditating on the third eye( a spot on the middle of your forehead) helps to calm you down a lot. By meditating, I do not mean doing the lotus position,etc. Just keep your focus there. The side effects however may be that you may start seeing visions. have loss of ego, etc much like smoking a lot of salvia does. However, after doing it a couple of times you will know your optimum point and will find out when to stop your 3rd eye meditation and get overly relaxed.
Sorry if my answer is not exactly what you are looking for. Perhaps instead of biology, a bit of psychology might be the answer you are looking for. Just my 2c.
Regards.
This is it. This is what it was. This is what it will be.