Aerosmith lead singer Steven Tyler has finally admitted he has a drug problem. After the rock star's legendary excesses of the past, such a move might not seem surprising. But there was more to Tyler's decision last week to check himself into rehab than first meets the eye.

The 61-year-old singer had long ago cleaned up his act and put his years of heavy drink and drug abuse behind him.

His current problem is different. He is addicted to painkillers, he announced - a dependence that began after taking medication to cope with 10 years of injuries from his performances.

Tyler's stage antics have left him with severe chronic pain and damage to his knees and feet. During a show this year he fell off a stage and broke a shoulder. Now he is addicted to the medicines he has used to kill the pain.

But the revelation of Tyler's problem is significant for more than its importance for Aerosmith fans. His is merely the most recent example of a growing US showbiz trend that has seen more and more stars admit prescription drug addiction, while cases of dependence leading to fatal overdoses have soared.

Among the deaths linked to prescription drugs are those of Heath Ledger, Anna Nicole Smith and Michael Jackson, a toll that was added to last week with the death of Brittany Murphy, star of 8 Mile and Clueless.

The 32-year-old actress died after collapsing at her Hollywood Hills home last Sunday.

Murphy's husband, Simon Monjack, vehemently denied she was addicted to prescription painkillers. But notes obtained from a Los Angeles coroner's office official say a formidable list of drugs was found in her room. The notes also said that "no alcohol containers, paraphernalia or illegal drugs" were discovered there.

Tragedies like these suggest the celebrity habit of pill-popping - sometimes known as pharming - is spreading alarmingly.

Early this year Burt Reynolds admitted he was "a prisoner of prescription pain pills" and checked into rehab, following a long list of stars, including Winona Rider, Charlie Sheen, Jamie Lee Curtis and Friends star Matthew Perry, who have admitted addiction to painkillers and other prescription drugs.

Such cases make headlines because they expose the lives of superstars.

But they are only the tip of an iceberg, doctors warn. In 2005, non-medical use of painkillers contributed to more than 8500 deaths in the US. Overdose deaths involving prescription pain relievers increased 114 per cent from 2001 to 2005, the most recent year for which nationwide figures are available, says the Office of National Drug Control Policy.

Prescription drugs are becoming America's new addiction, studies show.

In one survey of teenagers between the ages of 13 and 18 a total of 155 reported abusing prescription drugs obtained through a friend or taken from a medicine cabinet, sometimes by organising "pharming parties" where pills are put in bowls and shared with friends.

The practice has become common in rural areas - hence the use of the term "hillbilly heroin" to describe painkillers taken recreationally.

But why is this abuse growing? Is it confined mainly to young people, or are older individuals involved as well? And is this wave of addiction likely to spread to other countries?

These are questions that raise issues about attitudes to medicine in the West.

For a start, there is the issue of our faith in the medical profession.

Addiction to prescription drugs often arises as an accidental dependence to a drug first taken, and given, in good faith for a real ailment. For example, Michael Jackson is thought to have become addicted to demerol - or pethidine, as it is called in some countries - after being seriously burned during the filming of a Pepsi commercial in 1984.

Twenty years later, use had turned to abuse and Jackson was severely dependent, his staff revealed after his death.

"I think people of all ages don't take medication as seriously as street drugs," says Dr Marvin Seppala, the chief medical officer at Hazelden, a drug and alcohol treatment centre in Minnesota. "There's sort of a naive belief they're safer. The truth is pain medications are in the same exact class as heroin, morphine - they're very addictive."

This point is backed by the list of drugs found in Murphy's room.

The chairman of the British Pharmacology Society's prescribing committee, Professor Simon Maxwell, said he couldn't see how prescription of the medicines could be justified on medical grounds.

Liverpool University professor of clinical pharmacology Munir Pirmohamed said: "This is a horrendous list. Many of these are powerful medicines that are supposed to be prescribed for specific, serious conditions.

"Of course, there is always going to be a subset of people who want to experiment with substances. There are also individuals who want to take risks.

"But this is not the case with many of those addicted to painkillers and other prescription drugs. Many of these people simply do not realise that all drugs - no matter how beneficial - are poisonous at some level.

"That is the real key for dealing with this issue. We need to educate people to the dangers of all the medicines we consume."

* The drugs found in Brittany Murphy's room included:

Klonopin. An anticonvulsant also used to control aggressive behaviour. If taken with alcohol, it can lead to drowsiness or unconsciousness.

Fluoxetine. Sold under its trade name of Prozac, the drug is a powerful antidepressant. Side-effects include nausea and sleep problems.

Carbamazepine. Used to treat epilepsy and to stabilise patients' moods. It can also cause dizziness, drowsiness and liver problems.

Ativan. Used to treat severe anxiety, but can also cause drowsiness and muscle weakness.

Methylprednisolone. A powerful anti-inflammatory agent with side-effects that can can include psychosis.

Propranolol. A beta-blocker that is prescribed for high blood pressure and migraines. Its side-effects include disturbed sleep and shortness of breath.

Biaxin. An antibiotic given to people with skin and respiratory conditions, it can also produce nausea, hearing problems and chest pains.

Hydrocodone. A painkiller that can also cause nausea and convulsions.

Topamax. An anticonvulsant that is also known to cause headaches, nausea and diarrhoea in some patients.