A restriction on the number of painkillers that can be bought at supermarkets and chemists has led to a big cut in fatal overdoses, researchers have found.

Legislation introduced in 1998 limited the number of tablets in packets of common painkillers such as paracetamol and salicylates such as aspirin.

Packets of paracetamol sold in supermarkets can now contain only 16 tablets, those from chemists a maximum of 32. Any purchase of 100 or more tablets requires a prescription.

The general effect of the legislation is to reduce the maximum number of analgesic tablets available for impulsive self poisoning

Centre for Suicide Research

Previously, there was no limit on the number of tablets sold by chemists, while supermarkets could sell a maximum of 24.

Until the legislation was introduced the number of fatal overdoses involving painkillers had been rising steadily.

It is suspected that some people who have died did not realise how powerful painkillers can be, and had no intention to take their own lives.

First year

A team from the Centre for Suicide Research at Warneford Hospital in Oxford studied the impact of the change in the law in the first year after its introduction.

They found that the number of deaths from paracetamol poisoning fell by 21%, and from salicylates by 48%.

The number of liver transplants performed as a result of paracetamol poisoning also fell by two thirds.

Rates of non-fatal self-poisoning involving paracetamol fell by 11% in the 12 months following the introduction of the new law.

The average number of paracetamol tablets taken in an overdose fell by 7% and there was a 17% drop in incidents involving 32 or more pills.

Tighter controls

The researchers, writing in the British Medical Journal, suggest that even more deaths may be avoided if the maximum pack size was decreased still further - possibly to 24 tablets.

"Since the new legislation, pharmacies and other retail outlets have usually allowed only one pack to be bought per transaction," they say.

"Although this does not prevent a customer visiting several outlets to amass a large supply of the drugs, the general effect of the legislation is to reduce the maximum number of analgesic tablets available for impulsive self poisoning.

"An even smaller maximum pack size for pharmacy sales might have had a greater impact still."

Paracetamol is the most common way of self-poisoning in the UK.

Dr Geoffrey Brandon, director of the Paracetamol Information Centre, said: "Paracetamol is used safely and effectively by most people including pregnant women and children, so a reduction in its misuse is particularly welcome.

"Current pack sizes now strike a realistic balance between availability for the millions of people who need a safe and effective pain reliever, and the tiny minority who misuse medicines for purposes of self-harm."

Overdoses of drug are also responsible for half of all cases of liver failure in this country.

Before the new laws, overdoses of paracetamol accounted for 40,000 hospital referrals a year and between 100 and 150 deaths.

Aspirin overdoses accounted for about 5,000 hospital admissions annually and about 60 deaths.