Tobacco-Tobacco claims more lives than any other addictive substance in the United States. While it is legal, it can lead to extreme health complications.

Alcohol-Since it's legal for individuals over 21 years old in the US, alcohol is clearly one of the most commonly used drugs. Consequences of alcohol abuse include liver disease, overdose, lowered inhibitions, legal troubles, and more.

Painkillers-Painkillers like codeine, Vicodin, and OxyContin are prescribed to treat pain but are extremely addictive and can quickly lead to dependence.

Marijuana-Seeing as marijuana is sometimes used medically and is becoming decriminalized in states throughout the country, this substance is very popular in the US.

Heroin-Heroin, a highly addictive illicit drug, can quickly cause addiction. Those who abuse heroin are likely to experience intense withdrawal symptoms after use. Recovery from heroin is especially difficult and may require inpatient rehabilitation treatment.