Often these heroin users are under the misconception that if they do not inject the drug they will not become addicted. Those who have entered rehab to recover from heroin addiction include every method of heroin user. Annual admissions to substance abuse treatment for primary heroin abuse increased from 228,000 in 1995 to 254,000 in 2005; however, the proportion of primary heroin admissions remained steady at about 14 to 15 percent of all admissions. Between 1995 and 2005, inhalation and injection accounted for at least 94 percent of annual primary heroin admissions.

Heroin withdrawal begins as early as a few hours after the drug was last used. The body needs time to recover, and heroin withdrawal symptoms result. Heroin withdrawal can occur whenever any chronic use is discontinued or reduced. Users also experience severe craving for the drug during withdrawal, precipitating continued abuse and/or relapse. Major withdrawal symptoms peak between 48 and 72 hours after the last dose and typically subside after about a week; however, some individuals may show persistent withdrawal symptoms for months. Some people experience heroin withdrawal during hospitalization for health conditions other than their addiction. There are a few people in these circumstances that do not even realize they are experiencing withdrawal and think they just have the flu.

In 1885 the U.S. manufacturer Parke-Davis sold cocaine in various forms, including cigarettes, powder, and even a cocaine mixture that could be injected directly into the user.s veins with the included needle. The company promised that its cocaine products would .supply the place of food, make the coward brave, the silent eloquent and ... render the sufferer insensitive to pain..

Because of the way cocaine affects the mesolimbic reward pathway, cocaine is addictive. Nevertheless, cocaine is used in medicine as a topical anesthetic, even in children, specifically in eye, nose and throat surgery.