The MDA and its associated Regulations, the Misuse of Drugs Regulations 1985,⁹ lay down the circumstances in the UK in which it is lawful to import, produce, supply, possess with intent to supply, and possess drugs of misuse – "controlled" drugs. There are provisions within the Act for the Home Secretary to change the classification of drugs, through delegated legislation. Any submission by the Home Secretary for changes to the legislation by Order in Council or Regulation must be preceded by consultation with the Advisory Council on the Misuse of Drugs. This is the statutory body which keeps under review drugs which are, or are likely to be misused. It can appoint expert committees to consider specific issues and advises the Government on measures necessary for the prevention of drug misuse.

The penalties applicable to offences involving the different drugs are graded broadly according to the social harm attributable to a drug when it is misused and for this purpose the drugs are defined in three classes: A, B and C.

Class A Offences involving those in Class A attract the highest penalties – a maximum of seven years and/or unlimited fine for possession; life and/or unlimited fine for production or trafficking. A mandatory seven year sentence is now the penalty for a third conviction for trafficking.¹⁰ This class includes the more potent of the opioid painkillers (heroin, morphine, methadone¹¹, dipipanone, pethidine), hallucinogens (eg LSD, ecstasy) and the stimulant cocaine. Any Class B drug prepared for injection counts as Class A.

Class B has lower penalties: a maximum of five years and/or unlimited fine for possession; fourteen years and/or unlimited fine for production or trafficking. It includes herbal cannabis, cannabis resin, less potent opioids (codeine, pentazocine), strong synthetic stimulants (eg oral amphetamines), and sedatives (eg barbiturates). It also includes liquid cannabis, cannabinol and cannabinol derivatives (THC) (as of Jan 26, 2009)

Class C has the lowest penalties: a maximum of two years and/or unlimited fine for possession; five years and/or unlimited fine for trafficking. It includes tranquillisers, some less potent stimulants, and mild opioid analgesics (eg buprenorphine which is used in the treatment of opioid dependency).

Most offences involving drugs are triable either way, that is, summarily by magistrates or on indictment with a jury at a Crown Court. Less serious offences are usually dealt with by magistrates' courts, where sentences cannot exceed six months and/or £5,000 fine, or three months and/or fine for less serious offences. Eighty five per cent of all drug offenders are convicted of unlawful possession.¹³ Although maximum penalties are severe, just over 20 per cent of offenders receive a custodial sentence (even fewer actually go to prison), and nearly 3/4 of fines are £50 or less.¹⁴

The Misuse of Drugs Regulations 1985, made under the Act, divide the controlled drugs up in a different way to take account of the needs of medical practice. They define the classes of persons who are authorised to supply and possess controlled drugs while acting in their professional capacities and lay down the conditions under which these activities may be carried out. In the Regulations drugs are divided into 5 schedules each governing such activities as import, export, production, supply, possession, prescribing, and record keeping which apply to them. Details of the schedules are as follows:¹⁵

Schedule 1, the most restricted drugs, (eg, LSD and cannabis), can only be supplied or possessed for research or other special purposes by people licensed by the Home Office; these drugs are not available for normal medical uses and cannot be prescribed by doctors who do not have a licence.

All the other drugs are available for medicinal use. Most are Prescription Only, so they can only be obtained if prescribed by a doctor and supplied by a pharmacy (eg, strong analgesics like morphine, stimulants like amphetamines or cocaine, tranquillisers and most sedatives). Some very dilute, non-injectable preparations of controlled drugs - because they are so unlikely to be misused - can be bought over the counter without a prescription, but only from a pharmacy (eg, some cough medicines and anti-diarrhoea mixtures containing opiates). Medicines available in this way can also legally be possessed by anyone. The same also applies to benzodiazepine tranquillisers and hypnotics (except temazepam and flunitrazepam) even though these drugs can only be legally obtained on prescription.¹⁶

Schedule 2 includes such drugs as diamorphine (heroin), morphine, pethidine, cocaine. These are subject to the full controlled drug requirements relating to prescriptions, safe custody, the need to keep records, etc.

Schedule 3 includes the barbitrates (except secobarbital, now in schedule 2), buprenorphine, pentazocine, the tranquillisers nitrazepam and flunitrazepam. These are subject to the special prescription requirements, but not, for the most part, to the safe custody requirements, nor to the need to keep registers.

Schedule 4 includes benzodiazepines (other than flunitrazepam and tamazepam which are now in schedule 3) and anabolic steroids. Controlled drug prescription requirements do not apply and Schedule 4 Controlled Drugs are not subject to the safe custody requirements.

Schedule 5 includes those preparations which because of their strength, are exempt from virtually all Controlled Drug requirements other than retention of invoices for 2 years.

Additional regulations (the Misuse of Drugs (Supply to Addicts) Regulations 1997) effectively restrict the ability to prescribe heroin, dipipanone and cocaine for the treatment of addiction to a few specially licensed doctors. Solvents are not classified under the Act. However, under the Intoxicating Substances (Supply) Act 1985 it is an offence to sell solvents to someone under 18, and the Cigarette Lighter Refill (Safety) Regulations 1999, make it an offence to sell gas lighter refills containing butane to persons under 18 years of age.