According to the NHS, addiction can be defined as not having control over doing, taking or using something to the point where it could be harmful. It is most commonly associated with drug, alcohol, smoking gambling.

Substance Addiction is a mental condition that affects a person's brain and behaviour and leads to an inability to control the use of a legal or illegal drug or medication. Substances such as alcohol, cocaine, amphetamines, opioids, marijuana and nicotine are considered drugs. When a person is addicted, the person may continue using the drug despite the harm it causes.

Drug addiction can start with experimental use of a recreational drug in social situations and for some people, the drug use becomes more frequent. The repetition of its use forms a predictable habit pattern, even though the risk of addiction and how fast the person becomes addicted varies by drug. Over time, the person may need larger doses of the drug to get similar effects. As the drug use increases, the person may find that it's increasingly difficult to feel well without the drug. Attempts to stop its use may cause intense cravings and make the person feeling physically ill (withdrawal symptoms).