The reason humans, and mammals in general, are susceptible to getting high when smoking or ingesting cannabis is because cannabis produces a more powerful version of a number of chemicals our own bodies already produce.
The main agent of high is THC, a compound which is abundant in cannabis and which tricks our body into a stronger reaction compared to its naturally produced cannabinoids.
All vertebrates like mammals, birds, reptiles, amphibians and even fish have CB1 receptors whose function is to regulate the intensity of signals from the nervous system when these become too intense. When this happens, the brain releases its own natural cannabinoids similar to THC, which bind to the CB1 receptors and lower the intensity of the signal.
THC acts like our own endocannabinoids, but instead of acting only on those cells whose signals are too intense it affects all CB1 receptors all at once, with a much higher dose than is naturally produced and lasting for a much longer period of time
When nerve cells, primarily in the brain and spinal cord, become very active they release cannabinoids to dampen the incoming signal. The cannabinoids not only bind with the CB1 receptors to quiet the signal, but also puts a brake on the production of GABA, an inhibitory chemical which limits the production of dopamine, the body’s own natural pleasure chemical. The result is that dopamine levels increase for a short period of time.
Scientists believe that this endocannabinoid system (from the ancient Greek word endon meaning internal) plays a role in learning and motivation among other things, with the body rewarding the pursuit of difficult tasks like studying, running or repeating a movement to perfect it. To prove this scientists have tested blocking the production of cannabinoids in adult mice and have observed that these were less willing to work for a reward like food.
Our brains learn that certain signals are good predictors of a reward (for example following a light led to food in the experiment on adult mice) and our brain rewards the effort needed to pursue these signals by releasing cannabinoids which limit the production of dopamine-blocking chemicals thus giving us and the mice a dopamine hit, an incentive predicting that the real reward is about to come.
THC acts like our own endocannabinoids, but instead of acting only on those cells whose signals are too intense it affects all CB1 receptors all at once, with a much higher dose than is naturally produced and lasting for a much longer period of time. These receptors are common throughout the brain in areas like memory, coordination and senses explaining why cannabis can make us forgetful, clumsy, distort our sense of time, or make food and music feel more intense.
Seamus Walsh CC BY 2.0Cannabis, in many ways, is very similar to other drugs as nearly all addictive drugs end up boosting dopamine, but each one gets there by a different route.
Alcohol, for example, slows down our cells’ ability to communicate with each other making us overall slower, working in some ways like sleeping pills and anti-anxiety drugs. The end effect is that we are more relaxed, less anxious and less inhibited as alcohol targets the brain's alarm circuits, including fear and self-control, holding back impulses and thinking about consequences; and clumsier and slurring, as our coordination centers, our balance and our fine motor skills needed for speech are affected. Furthermore alcohol also affects the production of dopamine increasing our sense of pleasure and well-being.
Cocaine on the other hand, triggers the release of the body’s natural cannabinoids and hence increases the amount of dopamine in a way which mimics the effects of cannabis. However, its main effect is to block the removal of dopamine which the body normally takes care of, causing an accumulation and a much stronger high than cannabis or alcohol.
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