Prescribing training is being reviewed
Trainee doctors are not being given adequate training about the "complex" range of drugs available, a leading pharmacologist has told MPs.
Professor David Webb of Edinburgh University said the vast majority of newly qualified doctors are unsure about giving medicines to patients.
The General Medical Council, which oversees doctors' training, said it was reviewing the area.
But it said doctors had asked for more practical prescribing help.
Professor Webb told BBC Radio 4's Today programme: "My concern is that over the last 10 years medicine uses an increasingly complex amount of drugs but teaching about how to use medicines and prescribing has been declining.
"That is a problem, and needs to be addressed."
He cited a survey carried out two to three years ago of 2,500 medical students which found they were "very concerned about their ability to prescribe".
"The GMC has just published its own study in the same area and this highlights that of all the skills a new doctor requires, prescribing counts as an area where there is a problem and a potential risk".
Professor Webb appeared before the Commons Health Select Committee on Thursday to outline his concerns.
Deaths due to adverse drug reactions have risen by over 500% since the early 1990s and are now estimated to cost the NHS £500m a year.
But there is no direct evidence that the rise is linked to a lack of medical training.
Professor Peter Rubin, of the GMC, said medical students might think they needed more training, but that when questioned after qualification - when they were working as junior doctors - they did not want more pharmacology training.
However, he added: "What the students did say would be very helpful was towards the end of the course to have more experience in the practicalities of writing a prescription and we agree with that."
Training for doctors was changed in 1993 to put more emphasis on things like listening skills and less emphasis on prescribing skills.
The GMC is reviewing the document which sets out the standards for undergraduate medical education, 'Tomorrow's Doctors'.
Professor Webb said he was pleased with the changes he had seen in the draft.