Rimonabant is not recommended for people who are depressed
An obesity drug has been approved for NHS use in England and Wales, despite links to an increased risk of depression and suicide.
Rimonabant is already used by thousands of Britons, and, coupled with exercise, could help patients lose up to 10% of their body weight.
Scotland and the US have not approved the drug amid safety concerns.
However, an obesity specialist welcomed the National Institute for Health and Clinical Excellence (NICE) ruling.
In July last year, the European Medicines Agency warned that rimonabant may be unsafe for patients also taking anti-depressants, and NICE has echoed that advice.
Doctors have been told not to give it to patients with a history of major depression, and to be alert for new symptoms of depression in patients taking the drug.
Patients will not be allowed to have the drug, whose brand name is Acomplia on the NHS unless they have tried and failed using alternative drugs such as orlistat.
Evidence suggested one in 10 people might develop mental side-effects including low mood and depression, anxiety, irritability, nervousness and sleep disorders.
However, taking it can also lead to weight loss, but also improve general health, lowering blood pressure, and cholesterol levels.
Dr David Haslam, the clinical director of the National Obesity Forum, said that he welcomed its approval for NHS use, and predicted that it would be prescribed to many patients.
He said: "We can be absolutely reassured that they have looked closely at the evidence and made an appropriate decision.
"This is a very good drug, and there are very many people who have tried everything else, including other drugs, with little success, who might benefit from it."
But Professor Alan Alan Maryon-Davis, president of the UK Faculty for Public Health, said: "Whilst these drugs may be right for some patients, they are not the long-term solution and may have potentially serious side-effects.
"Ultimately the answer has to be: eat a little less and move a little more."
Rimonabant was first made available in the UK in 2006, and since then, the Medicines and Healthcare Products Regulatory Agency has received 720 reports of adverse drug reactions, covering 2,123 individual reactions.
Of these, 974 involved psychiatric disorders, including 48 reports involved suicidal thoughts, and a total of 93 involving depression.
A review of trial evidence published in the Lancet medical journal last year also found evidence that depression and anxiety were more likely in patients taking the drug.
Andrew Dillon, the chief executive of NICE, said: "The independent advisory committee recommended rimonabant, along with diet and exercise, as a treatment option for adults who are obese or overweight.
"This is good news for patients for whom orlistat and sibutramine are not effective."