GPs need to be more aware about the use of over-the-counter drugs and possible side-effects, leading doctors say.
More and more people are using over-the-counter drugs
The use of pharmacy medicine is rising as people try to manage their own health rather than going to a doctor.
But the British Medical Association study warned it can be dangerous to over-use pharmacy drugs and combine them with prescription medicine.
It said doctors should get training about such drugs and improve their record keeping.
The BMA also recommended pharmacy drugs be better labelled so patients know what the risks are.
The study gave the example of the herbal drug, St John's Wort, which can have adverse effects on prescribed medicines such as the contraceptive pill and anti-depressants.
And it also said eight in 10 people use over-the-counter drugs for headaches, but over reliance on them can lead to dependence.
Dr Vivienne Nathanson, the BMA's head of science and ethics, said: "It is extremely important that the public realise that just because medicines are available over-the-counter does not mean that they are risk-free.
"It is also important for doctors, especially GPs, to know if their patients are regularly taking any over-the-counter drugs.
"Doctors and pharmacists need to be aware that there are a minority of people who are at risk of misusing and becoming addicted to some over-the-counter medicines.
"Improved record keeping will help to identify this group."
Dr Jim Kennedy, prescribing spokesman for the Royal College of GPs, said it was an area of growing concern.
"A greater number and more powerful drugs are being made available over-the-counter, and coupled with this people are turning to herbal medicines and North American influenced food supplements.
"And the problem is that they don't think of them as medicine so don't tell GPs.
"There is also very little research about what effect these have on prescription drugs, so sometimes there is little we can say."