Addiction is the physical or psychological need to take a drug.
Addiction
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What is it?
Addictive drugs may include cigarettes, recreational drugs such as cannabis, ecstasy, cocaine, heroin and alcohol.
The user feels better physically or psychologically when they get another dose, and they're driven to repeat the experience.
What causes it?
The causes of addiction are complex but there's increasing evidence our genes may play a part.
A number of genes that may predispose us to addiction have been identified. The dopamine D2 receptor gene (DRD2) is more common among those addicted to alcohol or cocaine, for example, and may be linked to sensation-seeking or compulsive behaviour.
A recent study suggests that a gene found close to DRD2 - ankyrin repeat and kinase domain containing 1 (ANKK1) - may also be involved in addictive behaviour.
A gene for the transcription factor DeltaFosB may produce changes in the brain that contribute to addiction, by causing increased sensitivity to the effects of drugs.
Some genes for nicotine receptors may make some people more likely to smoke or find it harder to give up smoking.
Genetic factors that influence our ability to work, to make sound relationships or sense of personal discipline may make people more vulnerable to addiction.
What are the symptoms?
Symptoms include an overwhelming desire to seek out or experience the effects of a particular drug, often to the point where that need dominates the ability to lead a normal life. Everything revolves around the drug.
These symptoms depend on the nature of the addiction, and may also reflect long-term harm to the body.
Withdrawal symptoms commonly include agitation, anxiety and nausea.
What's the treatment?
There's no easy cure for addiction but new treatments are being developed that reduce addicts' cravings. Supportive rehab programmes and strategies are vital.
Antenatal testing isn't possible. Even if a baby carries a gene that may predispose it to addiction, other factors will determine whether an addiction actually develops.
Dr Rob Hicks last medically reviewed this article in October 2007
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