In the UK, an illegal or restricted drug. There are three classes with different legal penalties for possession and for dealing.

Class A drugs (the most harmful) include crack cocaine, cocaine, ecstasy, heroin, LSD, and magic mushrooms. Amphetamines prepared for injection are also class A drugs.

Class B drugs include cannabis, amphetamines, ketamine, methylphenidate, and pholcodein.

Class C drugs include anabolic steroids, gamma hydroxybutyric acid (GHB), khat, and some painkillers.

Drug use is governed by the Misuse of Drugs Act, 1971 and 2005. Some substances fall under the Medicines Act and are classified as prescription-only, pharmacist without prescription, or generally available.

https://www.drugwise.org.uk/what-are-the-uk-drug-laws/ Detailed information on UK drug laws from the DrugWise website