Scientists used to think that the rush of the neurotransmitter dopamine caused the feeling of euphoria (the “high”) during drug use, but we're learning that it’s more complicated than that.
Dopamine was sometimes called the brain’s “pleasure chemical.” Now we know it’s more like the teaching chemical.
What causes pleasure in the brain is still a bit of a mystery. But the brain’s “reward circuit” releases dopamine as a response to things that are pleasurable, like biting into a tasty treat, laughing with friends, or hearing a catchy song. Because of that surge of dopamine, the brain remembers these rewards and reinforces the desire to seek them out again.
Nicotine, cocaine, and marijuana affect the brain’s reward circuit. They can take control of the system, causing the brain to release large amounts of dopamine and "teaching" the brain to repeat the act of taking the drug.
With repeated drug use, the brain releases dopamine mainly in response to things that are associated with the drug.
For people who repeatedly use drugs, things in their environment could trigger the release of dopamine. For example, if they see a person who used drugs with them or if they visit a place where they used drugs, the brain could release dopamine in response. The result? An intense motivation to seek the drug again.
So, dopamine does not cause the feeling of euphoria (the “high”); instead, it reinforces the desire to use drugs.