Of 147 GPs surveyed, 83 per cent said they were forced to prescribe the bisphosphonate alendronate for osteoporosis because of cost, despite contraindications such as tolerability.
Two thirds of GPs admitted to changing treatments chosen by consultants for osteoporosis patients due to PCT restrictions.
Draft NICE guidance on osteoporosis states that alendronate is the only drug that PCTs have to prescribe for osteoporosis, leaving the provision of alternative drugs to the discretion of PCTs.
But alendronate is unsuitable for one patient in four.
The NOS is concerned that patients unable to take alendronate are left without a treatment alternative and put at risk of having serious bone fractures.
Of the GPs surveyed, 40 per cent want the draft guideline to be changed before NICE publishes the final document later this month.
Bradford GP Dr Anne Connelly, who has an interest in osteoporosis, said: 'NICE advises the use of alendronate because it is cheaper than other bisphosphonates due to its patent expiring.
'This restricts treatment options for patients who cannot tolerate alendronate, which can cause GI side-effects.'
Professor David Reid, chairman of the NOS medical board and professor of rheumatology at the University of Aberdeen, said: 'We know from this survey that alternative treatments can be withheld by PCTs unless they are recommended in the NICE guidance.
'Unless changes are made to NICE guidance, patients will go without and face the consequences. It is clear from this survey that NICE must rethink.'
NICE will announce its final guideline on 22 October. Alternative drugs to alendronate have already been approved in Scottish guidance.