Addiction is a strong mental and physical dependence on, most commonly, a drug or other substance. Some substances that can lead to addiction are alcohol, illegal drugs, some prescription medicines, inhalants (such as spray paint), and nicotine.

A person with an addiction usually has three or more of the following signs and symptoms:

• Needing more and more of the drug or substance to have the same effect, or getting less effect from the same amount of the drug or substance over time (tolerance)
• Being unable to stop using the drug or substance without having uncomfortable symptoms (withdrawal symptoms)
• Taking the drug or substance in larger amounts or over a longer period of time than was intended
• Being unable to cut down or control use of the drug or substance or having the persistent desire to do so
• Spending a lot of time getting, using, or recovering from the effects of the drug or substance
• Not being able to meet obligations to family, job, or other activities because of drug or substance use
• Continuing to use the drug or substance even though it is physically or psychologically harming the person

Most people with addictions also have strong cravings for the drug or substance.

The tendency to have addiction problems can be passed from parents to their children (inherited). This tendency often is accompanied by mental health problems, such as depression.