All drugs change the way the brain works by changing the way nerve cells communicate. Nerve cells, called neurons, send messages to each other by releasing chemicals called neurotransmitters, telling us how to act and behave. These neurotransmitters attach to molecules on neurons called receptors. (Learn more about how neurotransmitters work.)
There are many neurotransmitters, but dopamine is the one that reinforces cravings for pleasurable behaviors, like eating a piece of chocolate cake or playing a video game. With repeated use, stimulants like methamphetamine can disrupt how the brain’s dopamine system works, reducing a person’s ability to feel pleasure from normal, everyday activities. People will often develop tolerance, which means they must take more of the drug to get the desired effect. If a person becomes addicted, they might take the drug just to feel “normal.”
After the "high" of methamphetamine wears off, many people experience a "crash" and feel tired or sad for days. They also experience a strong craving to take methamphetamine again to try to feel better.
Learn more about how the brain works and what happens when a person uses drugs.