The Neurochemical Effects of THC
As told to me by my teacher, neuroscientist Dr. Thom Knoles, PhD.
The active ingredient in marijuana is tetrahydrocannabinol (THC), one of the most powerful sympathetic nervous system depressants commonly abused. The THC molecule weakly mimics part of certain bliss neurotransmitters, and it mimics them well enough to fill the receptor sites that are designed to respond to those endogenous brain chemicals associated with full-spectrum bliss.
The receptor gets "tricked" into triggering part of its bliss and de-excitatory repertoire. The THC molecule is capable of triggering only a limited range of the receptor cell's bliss repertoire (not all), but the first major cost is that THC blocks reception of many of the endogenous bliss chemicals released by meditation or other natural mood-elevating experiences.
Normally, after an endogenous molecule triggers the full-spectrum bliss response, the receptor expels the molecule, having "juiced" it, more or less.
However, THC is not endogenous, it is exogenous; that is, it's a drug from outside the human body. The first harmful consequence of this is that the receptor cannot eject the molecule for at least fifteen days - actually what happens is that after about fifteen days the contaminated cell dies and gets replaced.
Think of the way in which a poorly-cut counterfeit key may open a lock, but then cannot be removed from the keyhole. When the genuine key comes along, the keyhole is already filled and blocking entry by the true key. Then the locksmith has to replace the lock.
The millions of dead cells containing useless "stuck" THC molecules are scavenged from the body, and replaced by new cells that still carry a trace of the distorted memory of their contaminated predecessors, but can be rehabilitated to trigger their full repertoire if meditation becomes habitual and THC ingestion ceases.
The point here is when someone says "I only had like one puff (and I didn't inhale)", nonetheless, an incursion of millions of THC molecules into the body has occurred. In fact, the lungs are not laden with the greatest number of receptors - the greatest numbers exist in the mouth and nasal passages. That is why even passive THC smoke has a detrimental effect on the sympathetic nervous system.
An exogenous molecule is a "psychoactive drug" when:
1) it counterfeits a naturally occurring, endogenous substance for which receptors exist
2) it triggers part of the range of that receptor's repertoire, giving rise to a perceived desirable effect
3) it blocks the reception of endogenous molecules and thereby inhibits the cell's display of its full range, ultimately killing the receptor cell
4) it "trains" the cell to downgrade its expectation and settle for the limited range provided by the drug
5) its presence signals the body to cease production of endogenous bliss molecules because of perceived "plenty" in the receptors.
6) it causes dependency on the exogenous supply when the endogenous supply is "trained" to dry up.
Marijuana satisfies all these criteria in spades.
People who argue that marijuana is not addictive often are people who cannot stop easily. Marijuana is notoriously addictive.
It also induces long term intransigent unipolar depression and paranoia, and damages the immune system by suppressing t-cell production and anti-viral responses. People who breathe marijuana smoke get sick more easily and more often.
All this puts Maharishi Mahesh Yogi's reaction to marijuana in perspective. When asked what effect smoking ganja had for the sadhus who imbibed he said "it has a killing effect on spirituality".