system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 How does marijuana actually work?

When we smoke marijuana, what does it do to create the effect and the trip we see? And what are the side effects which makes it illegal in most countries around the world?
gpt
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.