Many medicinal products contain ingredients such as thickening agents which are derived from cotton, maize or wheat - plants chosen for genetic modification by big food and chemical companies.
Boots has said it would be "concerned" if it was unable to identify at source whether genetically modified (GM) maize or wheat was being used. It warned that if European suppliers mix up GM and non-GM crops, as happens in the US, then it will become impossible to know whether or not GM elements are present in its products.
Boots admits that may already apply to its own brand of liquid medicines, which use as a thickening agent an acid derived from cellulose, itself derived from cotton made in the US. "Cotton, like maize, can be sourced from the US and as such there is the possibility that a small quantity of a GM crop may sometimes be included," a spokeswoman said.
The announcement comes amid rising public concern at the widespread use of GM wheat, soya and maize in food products before they have been approved for commercial growth in the UK. English Nature, the Government's advisory body on environmental matters, has called for a moratorium on the growth of such crops while trials take place to monitor their effect on the food chain.
Boots' admission has been greeted with dismay by environmental groups such as Friends of the Earth, which is calling for a three-year moratorium on GM food sales until the Government conducts research into the risks. "We would be disappointed in Boots because it is doing it either in ignorance of public concerns or with total contempt," said Adrian Bebb, FoE food campaigner.
Boots, however, said it was sensitive to public worries over GM food. "We're concerned but we probably won't change the formulas for our products next year," said a spokeswoman. "In five years' time nobody is going to be able to give a guarantee over whether the product is GM or not because the US is taking over the market."
Monsanto, the US biotechnology giant, has been marketing GM products worldwide. A secret report for Monsanto, leaked to Greenpeace last month, quoted senior executives from Waitrose, Tesco and Safeway expressing anger at the high-handed way in which, they say, Monsanto brought GM food into Europe by mixing bioengineered soya products with normal ones.
Other concerns centre on starch, which is used for some Boots medical products. Starch is made from maize, which can be genetically modified, along with wheat and soya, to make it resistant to herbicides. Boots said it was certain its brand of paracetamol tablets did not contain GM starch. Boots is testing its food products for GM components and is working closely with suppliers to trace the origin of every ingredient.
Under European Union legislation, the majority of products containing GM ingredients will not be labelled since only those goods that have genetically- altered DNA in their end-product have to be labelled. The exemptions include any food that contains soya oil or soya derivatives such as lecithin. Starch, since it is an additive, does not need to be labelled if it has been genetically modified.
According to FoE, more than 15 per cent of all soya imported from the US is genetically modified and more than 60 per cent of processed foods contain soya. It also believes that up to 95 per cent of all foods that have used GM products in their preparation escape any need for labelling.
Concern has been mounting over the health risks of GM foods. Although GM soya and maize have been approved for safety in the US and Canada, FoE said there had been little independent testing of the implications of eating such foods. "We're concerned that if you cut and splice DNA there's a chance of something going wrong," said Mr Bebb.