Another one of the risks of heroin use is that all heroin users--not just those who inject the drug-- becoming addicted. Individuals who abuse heroin over time develop a tolerance for the drug, meaning that they must use increasingly larger doses to achieve the same intensity or effect they experienced when they first began using the drug. Heroin ceases to produce feelings of pleasure in users who develop tolerance; instead, these users must continue taking the drug simply to feel normal. Addicted individuals who stop using the drug may experience withdrawal symptoms, which include heroin craving, restlessness, muscle and bone pain, and vomiting.

Of high school seniors in 2001, 8.2% reported having ever used cocaine.

According to the UN's estimate, 141 million people around the world use marijuana. This represents about 2.5 percent of the world population.

Injecting Meth is a popular method for use, also known as slamming, but carries quite serious risks. The hydrochloride salt of methamphetamine is soluble in water; injection users may use any dose from 125 milligrams to over one gram using a hypodermic needle (Although it should be noted that typically street methamphetamine is "cut" with a water-soluble cutting material which constitutes a significant portion of that street meth dose).