In the United Kingdom drugs are regulated under the Misuse of Drugs Act. 1971 as either class A, class B or class C drugs.
Class A drugs are ones that are most prone to abuse and have the harshest penalties for possession without authority (like a prescription). They include: diamorphine (heroin) and other intravenous opioids (like pethidine, morphine, dipipanone, etc.), cocaine, lysergide (LSD), methadone, MDMA (ectasy), phencyclidine and class B substances when injected.
Class B drugs are amfetamines, barbiturates, cannabis, codeine, ethylmorphine, glutethimide, nabilone, pentazocine, phenmetrazine and pholcodine, which are drugs that can be abused and have a significant potential for abuse, but are less prone to abuse than class A drugs.
Class C drugs are drugs with minimal potential for abuse, like chlorphentermine, benzfetamine, buprenorphine, amfepramone, mazindol, meprobamate, pemoline, pipradol, most benzodiazepines, zolpidem, androgenic and anabolic steroids and other hormones with abuse potential.
Another act, the Misuse of Drugs Regulations 2001, divides drugs up into 5 schedules, in an analogous way to how they are divided in Australia and the U.S.
Schedule 1 consists of drugs that are not used medically, like lysergide, and are prohibited to possess, except with special authority from the Home Office.
Schedule 2 consists of drugs that are used medically but are of very high abuse potential like class A drugs.
Schedule 3 consists of drugs that are used medically and of a lower, but not low, potential for abuse than schedule 2 drugs. Examples are barbiturates (except secobarbital), buprenorphine, amfepramone, midazolam, pentazocine, phentermine and temazepam.
Schedule 4 consists of drugs found in class C.
Schedule 5 drugs are drugs that includes preparations of such strength, but low potential for abuse that they are subject to minimal control, aside from the requirement that any prescriptions and invoices are kept for 2 years.