Lack of training and time pressures mean many GP prescriptions contain either a prescribing or monitoring error, research reveals.
One in 20 prescriptions were found to have an error.
While most prescription errors were classed as "mild" or "moderate", around one in every 550 prescriptions was judged to contain a "serious error".
The most common errors were missing information on dosage, prescribing an incorrect dosage, and failing to ensure that patients got necessary monitoring through blood tests.
The PRACtICe study, commissioned by the General Medical Council (GMC), analysed the medical records and prescriptions of 1,777 patients across 15 practices in the country.
Over 900 million prescriptions were dispensed in England during 2010 with the vast majority being issued by GPs.
Those patients taking a lot of medication and are either very young or aged 75 or over are at an increased risk of prescription errors.
The GMC study places the blame for the errors on deficiencies in the training of GPs around safe prescribing, time pressures and poor use of computer systems.
"GPs are typically very busy, so we have to ensure they can give prescribing the priority it needs," said Professor Peter Rubin, Chair of the GMC.
"Using effective computer systems to ensure potential errors are flagged and patients are monitored correctly is a very important way to minimise errors. Doctors and patients could also benefit from greater involvement from pharmacists in supporting prescribing and monitoring."
The GMC has confirmed it will lead discussions with the RCGP, CQC and the Chief Pharmacist in the Department of Health to greater protect patients from prescription errors.
UK-wide medical defence organisation MDDUS has voiced its support for the GMC's move to improve prescribing standards, and said it hopes the study will alert doctors to the prescribing pitfalls and encourage them to take extra care.
Dr Clare Gerada, RCGP Chair of Council, said any error in GP prescribing is "regrettable" and is taken very seriously by GPs and their teams.
Last month Medical Education England backed the RCGP's calls for extended four-year GP training in what was described as a "momentous day for the entire medical profession".