The behavioral impact of habitual heroin use is generally devastating. Most habitual users are incapable of concentration, learning, or clear thought. Rarely are they able to hold a job. They are apathetic, indifferent to consequences, and unable to sustain personal relationships. For many, the inability to honestly earn enough to meet their drug needs leads to crime. For the overwhelming majority, compulsive use prompts behavior that is self-destructive and irresponsible, often antisocial, and characteristically indifferent to the injury, pain, or loss it causes others.

Meth is a powerful stimulant drug that increases brain activity. Short term effects, lasting up to 12 hours, include increased alertness, insomnia, hyperactivity, headache, decreased appetite, irritability, aggression, anxiety, nervousness, teeth grinding, convulsions and heart attack. Chronic abuse can lead to tooth decay, acne and skin sores (speed bumps), psychotic behavior, paranoia, hallucinations, rage, extreme violence, depression, fatal kidney and lung disorders and brain damage. Babies born to meth-using moms can be born addicted to meth and suffer birth defects, low birth weight, tremors and behavior disorders.

When cocaine is abused recreationally it is not often taken by mouth. Toxic reactions, including death, have occurred in people who swallow the drug to avoid police detection or border authorities. This smuggling attempt is known as body packing.

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.