I recently got into a bit of a debate about the neurochemistry of marijuana. Someone was asking if smoking pot would affect her SSRI. Someone replied that marijuana causes depression so it may cancel it out, to which I replied with what I knew which was this: where did you hear that pot makes you depressed? Perhaps amotivational syndrome could be a little depressing. But, marijuana doesn't affect the neurotransmitters (serotonine, dopamine, and norepinephrine) which are said to cause depression when the brain doesn't have enough of those happy little molecules firing back and forth, but instead it works on the cannabinoid receptors. Actually, cannabis is thought to have anti-depressant and anti-anxiety properties. Weed enhances all the functionings of the cannabinoid network. The primary functions of the cannabinoid network are believed to be regulating the immune cells and the sleep/wake cycle. There are lots of natural cannibinoids (as opposed to synthetic and endogenous) but the most common ones (and the ones present in marijuana) are: tetrahydrocannabinol (THC), cannabidiol (CBD) and cannabinol (CBN). There are two known cannibinoid receptors: CB1 an CB2. THC appears to moderate pain and to be neuroprotective and has a greater affinity for the CB1 receptors than for the CB2 receptors. Its effects are mostly cerebral. CBD seems to moderate the euphoric effects of THC and it appears to relieve convulsion, inflammation, anxiety, and nausea. CBD has a greater affinity for the CB2 receptor than for the CB1 receptor. It is thought to have more effect on the body. CBN is the primary product of THC degradation, and there is usually little of it in a fresh marijuana plant. CBN content increases as THC degrades in storage, and with exposure to light and air. It is only mildly psychoactive, and is perceived to be sedative or stupefying. Marijuana actually works as a stimulant and depressant as far as the central nervous system is concerned and that isn't related to depression. Rather, marijuana balances the autonomic nervous system (ANS) by its sedative / stimulant qualities which take place by its action on the hypothalamus part of the brain (the place from whence the autonomic system receives its instructions). The ANS is that part of our system which is responsible for all non-voluntary activity of the body / mind, such as rate of heart beat, size of pupils, rate of breath, chemical mixes in body fluids, etc. Stimulant effects of marijuana include an increase in pulse rate, blood pressure, and heartbeat. Some of the depressant effects are: relaxation, stress reduction, slowness, lethargy. Sorry, I didn't mean to turn this into some sort of lecture or something. I was just bored this morning and mainly decided to put this together as information for myself. --- To which she replied that it was in psychology textbooks that marijuana is said to decrease serotonin. I searched the net for more info on this, but many sites say different things: Some sites say that marijuana is a bit of an SSRI (this is probably why one would get depressed when quitting marijuana after long-term use I believe, that or it's just a case of the blues and learning to live sober), some sites say that it lowers serotonin, and some say that it has no effect whatsoever. I was wrong in saying that marijuana doesn't affect neurotransmitters, but the only neurotransmitters that I can find much reliable information about how cannabis affects the brain is some of the GABA receptors and of course anandamide. Does anyone know more about how cannabis affects other neurotransmitters such as serotonin and provide a legitimate unbiased source. I can't seem to find any good info.