Patients are dying and being seriously harmed because many doctors lack the sufficient knowledge to prescribe drugs properly, leading experts say.
Top doctors said the problem was being caused because the General Medical Council was placing less emphasis on pharmacology in UK medical schools.
They also said the risk was being compounded by the use of more complex medicines in the health service.
The GMC said it rejected the allegations completely.
The NHS spends £7bn a year on drugs, with an average of 12 prescriptions being written for each patient.
But the leading medics warned most of a doctor’s knowledge about how and what to prescribe was learned “on the job”.
They said a change in guidance to medical schools in 1993 by the GMC meant that there was less emphasis on prescribing skills.