The first scientific proof that an acne drug taken daily by thousands of British teenagers can cause depression has opened its makers to threats of fresh legal action, it was revealed yesterday.
Roaccutane, which is used to treat severe acne, has been blamed for hundreds of suicides around the world, including at least 15 in the UK.
However, its manufacturer, Swiss pharmaceutical giant Roche, has always rejected claims that the drug was responsible, claiming that severe acne can lower self-esteem and cause depression.
The new study - the first proof that the drug causes depression - leaves Roche open to a raft of multi-million-pound lawsuits mounted by patients who became depressed and relatives of those who took their own lives while on Roaccutane.
Last night, campaigners labelled Rocaccutane a "killer drug" and called for it to be banned in the UK, pending further research.
The calls centre around research from Bath University which showed that the drug, which has been given to British teenagers for more than two decades, causes depression in mice.
Biochemist Dr Sarah Bailey looked at how healthy mice were affected by a six-week course of Roaccutane, which has a similar structure to vitamin A.
She found that when given levels of Roaccutane equivalent to those used to treat teenagers, the creatures developed symptoms of depression, stress or despair.
Stressing that more research is needed to prove humans would be similarly affected, she said that her work was the first to provide clear evidence of the link, with previous human studies complicated by the psychological effects of severe acne and the mood-swings of adolescence.
It is not yet clear how the drug, which belongs to a family of compounds called retinoids, causes depression. It is thought it may lower levels of serotonin, a brain chemical known to boost people's mood.
Alternatively, Roaccutane may reduce the formation of new brain cells - something some experts believe may cause depression.
Dr Bailey looked at how adolescent mice - picked because they were in a similar stage of development to teenage children - reacted to regular doses of Roaccutane.
The creatures took part in two experiments, the journal Neuropsychopharmacology reports. In the first, they were placed in a tank of water that was slightly too deep for them.
Usually, mice try to escape, either by swimming or trying to climb out of the tank. But, these mice spent more time than expected completely still.
A second experiment, in which the creatures had to try to right themselves after being placed upside down, confirmed they had lost their will to fight.
Dr Bailey urged teenagers not to stop taking the drug. Instead, they should tell their GP if they start to feel depressed and parents should watch out for any mood changes in their children.
Since its introduction in 1982, Roaccutane, which is also known as isoretinoin, has been taken by tens of thousands of British teenagers.
Seen as a last resort, only to be used when all other treatments have failed, it is said to be almost 90 per cent effective in clearing up the most severe types of acne.
There are, however, claims it is being increasingly prescribed to treat more mild versions of the condition, with doctors finding it easier to write out a prescription than argue to case with distressed teenagers.
It is also taken by adults blighted by acne. However, fears that it can damage the development of the brain and spinal cord in unborn children has led to its prescription to women who may become pregnant to be tightly controlled.
GPs wrote out almost 6,500 prescriptions for Roaccutane tablets last year and a further 19,000 for a gel which as the same key ingredient.
Roaccutane's use, however, remains controversial, with the drug being linked to hundreds of suicides around the world, including at least 15 in the UK and almost 200 in the US.
It is estimated that up to 10 per cent of those taking the drug experience some degree of depression.
Only last year, the family of A-level student David Roberts blamed his death on the tablets. The 20-year-old was found hanged in a park near his Liverpool home three months after he began taking regular doses of Roaccutane.
His mother Anne told an inquest his family believed the medication had caused depression which went undetected.
In 1997 Seumas Todd, the 20-year-old son of veteran British actor Richard Todd, killed himself with a shotgun after taking Roaccutane.
His father, who starred in The Dam Busters and Alfred Hitchcock's Stage Fright, believes the drug was a factor in his death.
Last night, parents of victims called for the Roaccutane to be withdrawn until more research is carried out.
Muriel Hassett, whose 20-year-old son Luke was sectioned under the Mental Health Act after taking the drug, said: "This is a killer drug.
"I would like to see Roche put its money where its mouth is. It is a big company with a lot of money and it should be putting money into researching these adverse reactions."
Liam Grant, of the Roaccutane Action Group, blames the drug for the suicide of this 20-year-old son, also named Liam. He said: "I am entitled to a full hearing in a court of law.
"I will pursue this to the European court. I want Roche to admit that Roaccutane caused the death of my son."
Experts, however, stressed that Roaccutane has the ability to transform the lives of acne sufferers and the rate of side-effects is low.
Professor David Nutt, a Bristol University expert in the pharmacology of depression, said: "This research may help us to understand the mechanisms by which this drug may cause problems in humans and may also shed light on the biology of depression.
"However it's very important to stress that the only way to really find out whether this can be harmful to humans is to study with more precision the effects in humans."
Roche, which from 1988 has included warnings about depression and suicide on Roaccutane packets, said there was no proven link that the drug causes either depression or suicide.
A spokesman said:"Unfortunately, severe acne can cause some sufferers to become depressed and can also affect their mood and self-esteem.
"This is why the information provided with Roaccutane carries a warning that some patients may experience mood changes, including an increase in depression.
"The information leaflet, which is inside every pack of Roaccutane tablets, also tells patients that before they start taking the medicine they must tell their doctor if they are depressed, or if they have felt this way in the past." He added that the drug had "revolutionised" the treatment of acne.
The Government's drugs watchdog said it had closely monitored the drug's safety since its introduction.
Research carried out last year led to the recommendation that all new patients be told about the possibility of mood changes and monitored for signs of depression