THC and other cannabinoids (Such as CBD) bind to the cannabinoid receptors in our brain. These receptors are what mediates the psychoactive effects. Interestingly enough, these receptors also have their hands (so to speak) in other physiological roles in our bodies.
There is not a single side effect that makes it illegal.
Cannabis is illegal in many places because it gets lumped in with hard drugs, is misunderstood, or it’s a power move/control by the government.
Latest Answers