Patients should avoid seeing their GPs in the afternoon - because overworked doctors are drained of empathy by lunchtime, research suggests.
A study in the UK found that more than half of family doctors think they are working above safe limits, with some dealing with more than 100 cases a day.
GPs said that the overload was putting patients at risk and fatigue was leading to poor decisions, errors and irritability.
The polling of 1681 GPs by Pulse magazine found that they dealt, on average, with 41 patients a day while reckoning that 30 was a safe number.
One Hertfordshire GP said: "There is a point where I feel cognitively drained; after about 20 patients, there is not an iota of empathy left."
Dr Jonathan Harte, a Nottinghamshire GP, said the risks to safety grew as the day went on.
Describing his workload on the day of the snapshot survey, February 11, he said: "By lunchtime, I felt on the edge and risked missing urgent tasks and contacts, thus affecting patient safety."
Dr James Howarth, a GP in Spilsby, Lincs, dealt with 124 patients on the day of the poll.
"This creates patient safety risks," he said. "There are risks around having multiple patient notes open. We might forget consultant details, plans and actions, or prescribe for the wrong person, use the wrong labels on blood tests, and so on."
The survey found GPs work an average 11-hour day - eight hours of clinical care and three hours of administration.
The British Government has pledged to recruit 5000 more GPs by 2020, but has admitted that aim is unlikely to be met.
Professor Helen Stokes-Lampard, chairman of the Royal College of GPs said: "In my own practice recently, I had a 12-hour day and 100 patient contacts. GPs across the UK will tell similar stories."