Doctors will be asked to check their patients' diets more closely to ensure that mixing their medication and the food they eat does not result in life-threatening cocktails.
Government safety advisers are concerned that powerful drugs, already toxic by their very nature, may be made even more dangerous by interacting with ingredients in foods, drinks and supplements.
Alternatively, patients may unwittingly undermine the effectiveness of their medical treatments by eating the wrong foods.
Many patients may be taking up to 10 medicines at a time, officials say, meaning that the "potential for interaction in some individuals is great".
But there is unlikely to be any formal public education campaign or compulsory warnings on food products, despite some of the drugs concerned being prescribed to millions of patients.
There may be as many as 200 drugs whose action or toxicity is affected by food, according to advice being drawn up by advisers to the the Food Standards Agency and the Medicines and Healthcare products Regulatory Agency (MHRA). It follows a day-long meeting between experts on the committees on the toxicity of food and on the safety of medicines.
Some safety advice has previously been issued to doctors and other prescribers such as pharmacists and nurses. This has included the potentially lethal combinations of the anti-coagulant warfarin and cranberry juice, anti-cholesterol drugs known as statins and grapefruit juice, and oral contraceptives, antidepressants and anti-HIV drugs and the popular herb St John's wort.
But less is known about other interactions, including how milk and dairy products might reduce the effectiveness of antibiotics taken for respiratory and genital infections, for instance.
New foods such as probiotic yoghurts and dairy drinks, designed to improve people's health by changing the microflora in their guts, might lead to more food-drug interactions.
A phytoestrogen found in soy sauce might affect hormone control and therapy such as tamoxifen, the breast cancer treatment.
Government-backed efforts to reduce the amount of sodium salt in the diet might also cause a problem. Although this may reduce the risk of high blood pressure, heart attacks and strokes in the population as a whole, people cooking at home and food manufacturers may turn to potassium salts instead. But this could cause a problem for people taking diuretics, or who are on some anti-arthritis drugs or on drugs that manage high blood pressure.
Not all combinations will be dangerous. Indeed, sometimes patients who are responding well to drugs may be better off staying with their existing diets.
Milk and dairy products are widely consumed, just like antibiotics, so in practice any interactions are unlikely to be life-threatening, suggests a draft paper on the subject.
However there have been at least two deaths linked to the intake of cranberry juice with medication. There is also little data on which groups are most vulnerable to food-drug interactions, although they are likely to include children and frail, elderly people.
The paper concludes that most people will not be affected; therefore there should not be more public information, but instead better awareness among doctors and other prescribers, even though many patients do not tell them when they are taking herbal or complementary medicines that might react with conventional drugs.
"In some cases practitioners have built up knowledge about interactions in specific groups of patients taking particular drugs, such as the interaction between St John's wort and anti-HIV drugs. It would be helpful for this type of information to be more widely disseminated."
The Food Standards Agency said yesterday that the advice to government was not yet complete. The issue of how people were told about such interactions was a matter for the MHRA, a spokeswoman said. "It is really GPs who are best placed to advise their patients when prescribing."
Avoiding interaction: what not to mix
Warfarin to prevent blood clotting
Reacts with cranberry juice and green vegetables. Efficacy may be reduced by ice cream, soya beans and avocados, although clinical significance and prevalence of this problem is unclear
Cholesterol-lowering or immunosuppressant drugs
Patients should not drink grapefruit juice
Sedatives; other drugs including paracetamol
Should not be mixed with alcohol
Lithium to treat bipolar disorder
Patients must not vary intake of salt once they have been stabilised on the drug
Oral contraceptives; anti-depressants in the SSRI class; anti-HIV drugs
Do not mix with St John's wort, even though there is evidence that it can help treat depression too
Antibiotics in the tetracycline and quinolone classes
Milk and dairy products can reduce their effectiveness
