Around one in 20 prescriptions written by family doctors contain an error, according to a study published today.
Most mistakes were classed as mild or moderate, but around one in every 550 items was judged to contain a serious error, the research commissioned by the General Medical Council (GMC) found.
The most common of the prescribing or monitoring errors were lack of information on dosage, prescribing an incorrect dosage, and failing to ensure that patients were properly checked with blood tests.
One in eight of all patients had a prescription item with an error - this rose to four in 10 patients aged 75 years and older.
A number of factors were found to be associated with increased risk of prescribing or monitoring errors and these included the number of medicines a patient was taking (there was a 16% increased risk of error for each additional medicine) and the age of the patient (children and those aged 75 years and older were almost twice as likely to have an error as those aged 15-64).
Researchers concluded that causes included deficiencies in the training of GPs regarding safe prescribing, time pressure, and lack of robust systems for ensuring that patients receive necessary blood tests.
Despite these concerns, they found that GPs took prescribing very seriously and used a range of strategies to try to avoid serious errors.
Professor Tony Avery of the University of Nottingham's medical school, who led the research, said: "Few prescriptions were associated with significant risks to patients but it's important that we do everything we can to avoid all errors.
"GPs must ensure they have ongoing training in prescribing, and practices should ensure they have safe and effective systems in place for repeat prescribing and monitoring."
The researchers recommended a greater role for pharmacists in supporting GPs, better use of computer systems and extra emphasis on prescribing in GP training.
Professor Sir Peter Rubin, chairman of the GMC, said: "GPs are typically very busy, so we have to ensure they can give prescribing the priority it needs.
"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.
"We will be leading discussions with relevant organisations, including the Royal College of General Practitioners and the Care Quality Commission, and the chief pharmacist in the Department of Health, to ensure that our findings are translated into actions that help protect patients."
The study took place in 15 general practices from three areas of England, regarded as reasonably representative of other general practices in England, and a total of 1,777 patients were included in the study.
Dr Clare Gerada, Royal College of General Practitioners (RCGP) chair of council, said: "There are over one million patient consultations in general practice every day across the UK, and this report demonstrates that in 95% of cases GPs prescribe safely and effectively in the best interests of their patients.
"GPs strive to keep their prescribing skills up to date to provide the safest possible patient care, but any error is regrettable and taken very seriously. The report helpfully identifies some areas where improvements can be made."
Health Secretary Andrew Lansley said: "Patient safety is paramount. The vast majority of prescriptions are checked by community pharmacists, who spot and put right any errors when they are dispensed. Patients can be confident that the medicines they receive are safe and appropriate.
"We have worked to improve and increase the training medical students receive in prescribing skills, and we are working with GPs to see how we can best support them to work with pharmacists and improve the safety and effectiveness of prescribing.
"We will continue to work with pharmacists and GPs to reduce prescribing errors and make the best use of medicines."