Drugs and alcohol are processed by a part of the brain called the ventral tegmental area, more commonly known as the "reward center." It's where the brain processes anything that makes a person feel good. The reward center is responsible for producing a chemical you've probably heard of: dopamine.
An article for Slate explains that dopamine -- while famous for being held responsible for everything from love to drug addiction -- is just one chemical of many that affect human behavior. From Slate:
What is dopamine? Dopamine is one of the chemical signals that pass information from one neuron to the next in the tiny spaces between them. When it is released from the first neuron, it floats into the space (the synapse) between the two neurons, and it bumps against receptors for it on the other side that then send a signal down the receiving neuron.That sounds very simple, but when you scale it up from a single pair of neurons to the vast networks in your brain, it quickly becomes complex. The effects of dopamine release depend on where it’s coming from, where the receiving neurons are going and what type of neurons they are, what receptors are binding the dopamine (there are five known types), and what role both the releasing and receiving neurons are playing.
So it's not as simple as "dopamine goes in, bad behaviors come out." It's not even as simple as saying that dopamine makes you feel good.
When you have sex, do drugs, or partake in something else you find pleasurable, you end up with high levels of dopamine in a part of your brain called the nucleus accumbens.
Once it's there, dopamine does something kind of crazy. It doesn't exactly make you feel good on its own, but it signals to your brain and body that you should pay attention to the action you just took, and associate it with the feelings it just produced.
Some drugs can elevate dopamine levels to as much as 10 times higher than normal. And if a person starts taking those drugs regularly, the brain will adapt to the massive dopamine overload by reducing its number of receptors for the chemical.
That means an addict may end up needing more and more drugs to sustain the same high. Meanwhile, everyday producers of dopamine, such as food and hugs, will seem way less enjoyable than they did before, because they can't trigger enough of a dopamine rush to get noticed.
But breaking the cycle isn't impossible. If you or someone you know needs help recovering from addiction, check out the resources available on the National Recovery Month Web site.