An advertisement for a new contraceptive pill used by thousands of women in Britain, which claims to help them avoid weight gain and give them a sense of well-being, has been condemned as misleading by experts.

The Government's Medicines Control Agency (MCA), which regulates the promotion of medicines, has found there is insufficient evidence to support the claims made for the pill and has ordered the advert to be withdrawn.

Thousands of British women have been put on the pill - brand-named Yasmin and produced by Schering Health Care - because their GPs were told that, unlike other contraceptive pills, it would not make women put on weight. The manufacturers also claimed it had a 'demonstrable positive effect' on pre-menstrual symptoms and skin conditions.

Schering launched the pill this year, with adverts showing an attractive, smiling woman in soft focus alongside the strapline: 'The pill for well-being'.

The advert has now been withdrawn on the orders of the MCA. After giving the advert the all-clear in June, it scrutinised the evidence again and found that some of the claims in the colour adverts published in the medical press could not be supported.

The Yasmin saga will raise concerns about the way products are marketed, amid concern that controls on the industry are not strong enough. Although advertising directly to the public is banned in the UK, it is thought that US-style promotion of drugs to consumers may eventually be allowed.

Dr Joe Collier, editor of the Drug and Therapeutics Bulletin , which first raised concerns about the adverts, said: 'There should be a full inquiry into how the MCA, which is partly funded by the pharmaceutical industry, allowed this advert to go through. This level of incompetence, which would appear to favour the industry rather than public health, is totally unaccept able. When doctors advise women about their choices of contraception, they need to be fully, properly informed.'

Like all 'combined' contraceptive pills, Yasmin contains two active ingredients - an oestrogen and a progestogen. But it differs from others in that it contains a new type of progestogen called drospir-enone, which is said to be closer to the natural form of the hormone and inhibits some of the fat-inducing effects of the other pills.

It is now taken by more than a million women worldwide, including thousands in Britain attracted to the idea of having a contraceptive that will not leave them feeling bloated, spotty or overweight.

But the product is also expensive. At £59 for 12 cycles of treatment, it costs the NHS up to eight times more than any other combined oral contraceptive.

In June, the MCA wrote to Schering, saying: 'Based on the information you supplied to us and the current state of scientific knowledge, it appears to the MCA that there is no current basis for taking any action in relation to this advertisement.'

However, Dr Collier continued to fight for some action. The industry's own watchdog committee, the Prescription Medicines Code of Practice Authority, began to look at it in August.

In September, Schering threatened to sue the Bulletin - which is owned by the Consumers' Association - on the grounds that its articles criticising the adverts were defamatory. Its lawyers said the Bulletin's article had led a number of primary care trusts to decide not to approve Yasmin as an option for contraception.

But the industry panel found that the advert breached its code of practice on 10 counts. Most importantly, it concluded: 'The panel considered that the claim that Yasmin had been shown repeatedly to have no associated weight gain was a strong, absolute claim which did not reflect all of the evidence and was misleading in that regard, and could not be substantiated.'

They also concluded that the claim by Schering that Yasmin was 'truly different' and had a positive effect on skin condition could not be substantiated.

The drugs company temporarily withdrew its legal threat to the Bulletin , but decided to appeal against all the panel's rulings that it had breached the code of practice. The MCA then carried out a more in-depth scrutiny of the drug and found there were grounds for concern. 'The advertising for the product that was the subject of a complaint has been withdrawn on a voluntary basis at the request of the MCA following a rigorous examination of the claims made,' it said.

But Schering stands by its claims. 'We believe that the claims made do accurately reflect the data which was published in peer-reviewed journals. We can't comment further as we are going through an appeals process.'