Although we understand that illicit drugs like cocaine, heroin, and methamphetamine can be addictive to a life-ruining extent, it can still be hard for many of us to appreciate how that happens.
Indeed, each of these drugs works differently but end up having similar effects of teaching the brain to expect and depend on certain chemical circumstances. According to McGill University, cocaine does this by blocking transporters that normally remove excess levels of dopamine from the brain's reward circuits.
If the drug is used frequently enough, this not only makes the brain get used to these artificially elevated levels of dopamine, but actually influences it to build new receptors for the brain chemical.
This explains why addicts feel depressed and crave the drug so intensely when it runs out, but one TikTok user explained how the race to alleviate those feelings over the course of his adult life all but ruined it.