Further concerns have been raised about potential suicidal side effects of a commonly used antidepressant.
The researchers looked at 1980s studies into Seroxat
The drug Seroxat (paroxetine) is already banned from use by adolescents because of an increased risk of suicidal thoughts.
In the journal BMC Medicine, University of Oslo scientists said existing studies indicated these warnings should be extended to adults.
GlaxoSmithKline, which makes the drug, said it had helped millions.
Paroxetine is one in a class of drugs known as Selective Serotonin Re-uptake Inhibitors (SSRIs).
In 2003, around 19 million prescriptions for SSRIs were handed out in England for the treatment of depression and anxiety.
Concerns over suicidal side effects for those taking paroxetine were first raised by the BBC's Panorama programme in 2002.
Last year the Medicines and Healthcare products Regulatory Agency's (MHRA) Committee on Safety of Medicines concluded that a modest increase in the risk of suicidal thoughts and self-harm for SSRIs could not be ruled out, but the benefits for adults outweighed the risks.
The Norwegian researchers, whose study was triggered by a journalist from the Norwegian Broadcasting Corporation working on a medical information programme, analysed the results of 16 trials involving the drug.
The studies were presented to drug regulatory agencies in 1989, prior to the drug being licensed for use by doctors in the early 1990s.
In each, patients had either been given paroxetine or a placebo (dummy pill).
The researchers carried out a statistical analysis of all the results, taking into account the length of time patients were on the drugs.
The studies included 916 patients on paroxetine and 550 patients on placebo.
There were no actual suicides in any of the studies. However, there were seven suicide attempts in the group on paroxetine, and only one in the placebo group.
Writing in BMC Medicine, the team led by Dr Ivar Aursnes, said: "Patients and doctors should be warned that the increased suicidal activity observed in children and adolescents taking certain antidepressant drugs may well be present also in adults.
"We also conclude that the recommendation of restrictions in the use of paroxetine in children and adolescents conveyed by regulatory agencies lately should include usage in adults."
A spokesman for GlaxoSmithKline: "We take the safety of all our medicines extremely seriously and will, of course, review this study carefully when it becomes available."
He added: "At this stage, it's not clear what method the researchers have used to arrive at these numbers or which clinical trials they have selected.
"However, we can say that these conclusions in no way reflect the picture that has been built up about the benefits and risks of paroxetine in adults through an extensive clinical trials programme involving 24,000 patients or through the use of this medicine in tens of millions of people around the world."
An MHRA spokeswoman said it kept the safety of all SSRIs under close review and all new evidence was carefully reviewed and considered to see if new advice was needed.
Sophie Corlett, director of policy at the mental health charity Mind, said: "This study would seem to be an extremely worrying addition to growing evidence raising serious concerns over the safety of paroxetine.
"It confirms what Mind service users have long been telling us anecdotally.
"By ignoring what mental health service users themselves have said about the medication and its effects, the drugs regulators may well have caused lives to be lost."
Margaret Edwards, of the mental health charity Sane, said: "Seventy per cent of those being treated with the new anti-depressants respond well, and the risks of suicide from untreated depression must be borne in mind in balancing the risks and benefits."