Many drugs can change your physical appearance as well as damage your body from the inside out. Drugs like meth and others alike cause an individual to not feel hunger, so they don't tend to eat and become very underweight and unhealthy. Drugs can also cause a lack of luster to the hair, skin and nails. But other than the superficial stuff, using substances can cause liver damage, cause a weak heart, make it harder to fight off infection and even cause death.

Tolerance is a person's diminished response to a drug that is the result of repeated use. It is another physical effect of repeatedly using drugs. Tolerance occurs because when an individual take a certain drug for an extended period of time, the receptors or enzymes in the brain and body are less activated by the drug, therefore it becomes less effective. So, in order for an individual to experience the same high they once had, they now have to increase the dosage they have each time so that they experience the same effects. This is how people tend to overdose or even switch to harder drugs; because they have built up a high tolerance.