The UK's drug regulator recommended that patients start on the controversial cholesterol-lowering drug Crestor at half the dose that ultimately went on the market, the Guardian has learned.

In January 2003, the Committee on Safety of Medicines recommended that patients be started on a 5mg dose of the drug, rather than the 10mg preferred by the manufacturer, AstraZeneca. However the drug was launched in March that year in line with the drug firm's request. This is because the European regulatory process uses the views of several countries, and national regulators have the choice of going with the European decision or not approving the drug at all.

The CSM's views appear to have become more widely accepted, because last November the European regulator said it was looking at whether to start all patients on 5mg, or just people at risk of serious side-effects, due to differing views on "public health concerns".

The drug has been dogged by controversy over its safety, with campaigners claiming it produces a higher rate of a potentially fatal muscle disorder known as rhabodmyolysis. AstraZeneca regularly publishes statistics that show a similar rate of side-effects as other cholesterol-lowering drugs, known as statins, with one patient in 100,000 afflicted with the muscle disorder.

However, confidential documents the Guardian obtained under the Freedom of Information Act this month showed that the UK regulators had seen higher rates of rhabdo in Crestor patients than other statins, prompting restrictions on the highest dose on the market, 40mg, last year.

The documents revealed that the CSM also recommended in January 2003 that this higher dose should not go on the market, two months before it was launched. It originally said that only patients with an extremely rare genetic disorder should be given the dose. Up to 4,500 patients had been given the 40mg dose by the time its use was restricted in June last year.

The regulators acknowledged that the increased rate of rhabdo could be due to a bias in the level of reporting of side-effects following the with drawal of the cholesterol lowering statin Baycol in 2001, which was linked to more than 100 deaths, or Crestor could be more toxic. AstraZeneca has said that the restrictions put on the 40mg dose last year have led to a reduction in the rate of rhabdo to normal levels.

The FOI request revealed minutes of meetings on the safety of the drug although a substantial proportion of the information was blacked out. The reason given by UK drug regulator, the Medicines and Healthcare Products Regulatory Agency, was that the information related to ongoing regulatory action and so its release might harm the commercial interests of the company.

One blacked out minute, under "major public health concern", is understood to be the recommendation that patients start on 5mg from scientists on the CSM, which is the expert panel within the MHRA.

AstraZeneca would not comment on what the withheld CSM minutes say. It has pointed out that the drug has been approved by more than 70 authorities worldwide and has been prescribed over 17m times to more than 4.3 million patients. It also said: "Within the drug approval process it is usual that there will be different views expressed by member states at different time points."