According to research commissioned by the GMC, some doctors are working 100 hours a week during their busiest weeks, which increases the potential for mistakes.
Under the UK's Working Time Regulations the 55,000 doctors in training should not be working more than 48 hours a week, averaged over 26 weeks. They are also bound by the Junior Doctors New Deal contract, which was designed to limit the hours they can work.
The GMC study, based on the views of 82 trainee doctors, found that while the regulations had led to fewer hours, they had also produced more shift work, leaving some doctors suffering fatigue and acknowledging that there were times when they performed poorly.
Director of the NHS Employers organisation, Dean Royles, said the report would reinforce the view that junior doctors' contracts should be renegotiated.
Royles said: "The European Working Time Directive (EWTD) is often blamed for stopping junior doctors finding time to train and develop their skills.
"Employers believe that improvements to the junior doctors' contract would streamline their working patterns, releasing time to train and provide quality care while keeping within the hours set by the EWTD."
The study also found that among the respondents:
- Most felt unable to challenge bad rotas and working practices.
- Some reported not being able to take rest breaks or eat or drink during long shifts.
- Working Time Regulations were not the sole cause of fatigue and its impact on patient safety - the researchers suggest doctors' experiences cannot be isolated from other changes to medical education and the NHS.
Niall Dickson, chief executive of the GMC, warned that trainee doctors must never go back to working the "ridiculous" hours of the past, when "exhausted" young doctors routinely put patients at risk.
Dickson said: "It is clear the current system is not working as it should. In some cases doctors are still too tired and there are issues around continuity and training opportunities.
"The current system is too complex and the way it is implemented is far from satisfactory," he said.
Royles added: "Improvements to the junior doctors' contract, in particular, could greatly benefit both staff and their patients.
"The services the NHS provides and the way it provides them have changed significantly since the contract was initially drawn and as a result, it is no longer fit for purpose.
"A renegotiated junior doctors' contract could simplify processes, increase the focus on patients, enhance training opportunities and achieve less rigid shift patterns."
The GMC research was aimed at understanding the impact of the Working Time Regulations, which are intended to promote health and safety by restricting the hours doctors work.
