Women who take Britain's most popular fertility drug for more than a year are at increased risk of ovarian cancer and should be regularly screened for the disease, according to a leading gynaecologist.
More than 1,000 women could be affected, said Stuart Campbell, professor of obstetrics and gynaecology at King's College School of Medicine.
The drug, clomiphene citrate, which stimulates the ovaries to produce eggs, is taken by 16,000 women a month to help them conceive. More than a million women may have taken it since it first came on to the market under the brand name Clomid in 1966. Since then a second version has been launched.
Although the vast majority of users only take it for four to six months, some women continue on it for considerably longer.
Professor Campbell warns that such prescribing is dangerous. "A recent paper in the New England Journal of Medicine showed that women who had been on it for more than a year had a considerably increased risk of cancer.
"We do not know whether they are at increased risk because the drug causes super-ovulation [the production of many eggs] or because it is an oncogenic [cancer causing] drug, in its own right. But women who have been on it for over a year should be regularly screened by ultra-sound."
The Committee on the Safety of Medicines is also concerned about the drug's long-term effects. In its Current Problems bulletin, it states: "Recently it has been suggested that clomiphene increases the risk of ovarian cancer ... We recommend that it should not normally be used for more than six cycles."
The report in the New England Journal last year which sparked off the worries suggested that taking the drug for more than a year increased the risk of ovarian cancer 11-fold.
At present, no screening programme exists for the disease, which kills 4,000 women a year. Although it is less common than breast cancer (5,000 cases a year, compared with 28,000), the cure rate is worse because it is usually detected very late. The five-year survival rate is 28 per cent, compared with 62 per cent for breast cancer.
Peter Bromwich, medical director of the Midland Fertility Services clinic, said: "It must be remembered that ovarian cancer is much less common than breast cancer, so even if the risk is increased, it is still small. Clomiphene is a damn good drug if it is used sensibly."
Susan Rice, chief executive officer of Issue, the national fertility association, said: "We do not think anyone should be on it for more than a few months. If it is going to work, it is going to work within that time anyway." She added: "We would advise anyone who has been on it for more than a year to see their doctors and consider asking for screening."
Howard Jacobs, professor of reproductive endocrinology at University College London and chairman of the British Fertility Society, said: "The paper in the New England Journal is flawed. The women who develop cancer in the study had several different kinds and it is unlikely that there is one cause ... But it reminded doctors that no drug is without side-effects. I see women who have been on clomiphene for years. That is irresponsible prescribing."
Dr Mercia Page, of Serono UK, makers of Serophene (a brand name for clomiphene), said: "The data sheet recommends no more than six cycles. If a patient has had several cycles and not conceived, the doctor should be thinking of moving her on to a different drug."Reuse content