A leading osteoporosis specialist has resigned from the government's medicines watchdog because he disagrees with a health warning issued on hormone replacement therapy.

Professor David Purdie said he did not agree with the Committee on the Safety of Medicines (CSM) that HRT should no longer be the first choice treatment for preventing the bone disease.

The disagreement follows studies showing that the treatment slightly raises the risk of breast cancer, blood clots and strokes.

The advice from the Medicines and Healthcare products Regulatory Agency (MHRA) yesterday followed a Europe-wide review of the risks and benefits of the therapy, most commonly used to relieve the symptoms of the menopause. But the resignation of such a respected figure over the advice is likely to add to the confusion felt by some women receiving the treatment.

Prof Purdie, who is based at the Edinburgh Osteoporosis Centre, a private diagnostic unit, said: "I believe that GPs should retain the option to use HRT in women in their early 50s to prevent osteoporosis.

"I think HRT is effective, reliable and safe in preventing osteoporosis. I believe women can use HRT when they are younger and then move on to non-hormonal treatments later on."

He believes that there has not been enough time for a full and thorough international assessment of recent research on the treatment. He added: "HRT is used for symptom control of the menopause and for bone loss. It does both superbly well. There is no such thing as absolute safety".

Prof Purdie said he believed the committee had rushed forward in issuing the advice without allowing time for the research to be properly reviewed.

He felt he had to resign because he disagreed with the MHRA's advice and believed HRT still had an important role to play in preventing osteoporosis, particularly in younger women.

A spokesman for the Department of Health confirmed that Prof Purdie had tendered his resignation from the CSM.

She said: "He should have made his concerns known before the advice was submitted. We stand by the advice that HRT can be used in the short-term treatment of post-menopausal symptoms but should no longer be the first choice for the prevention of osteoporosis."