Chemicals in drugs interact with the natural chemical messenger dopamine in the brain. Addictions to any of these drugs affect the user's state of mind and can ruin lives. Beginning users do not anticipate their craving for the drug and expect to quit when they want. Continued use builds up a resistance to the drug, so users take more to feel the euphoria. This process grows into a heavy addiction.
Abusers often resort to stealing and selling drugs in order to fund their addictions.
Thus, illegal drugs cause a much higher crime rate. In addition to the short-term problems with drug abuse, it can affect users much later in life, also. A deadly spiral is set up, making it more and more difficult for the addict to quit. Continued drug abuse becomes increasingly a matter of brain damage and less a matter of weak character. Besides the physical effects of the chemical and addiction, substance abuse can also lead to long term brain damage.