Researchers at the University of Nottingham, which is carrying out the £580,000 study for the DoH's Patient Safety Research Programme, say such medication errors by GPs cause one hospital admission in 15.
The three-year study aims to pinpoint areas of weakness in prescribing practice.
The researchers will focus on prescribing patterns known to be associated with patient health problems: for example if patients are put on to drugs not appropriate to their medical history, or where they are prescribed drugs without regular tests to ensure they are tolerating the treatment.
One outcome might be that pharmacists work more regularly with GPs to pick up potential problems before patients are put on to inappropriate drugs.
Study leader Professor Tony Avery, head of the division of primary care at the University of Nottingham, said it was often weeks or months before patients suffered ill effects.
The study will involve 68 GP practices across Nottingham and Manchester.
They will assess the benefit of pharmacists spending two days every 12 weeks giving feedback on prescribing practices.