The number of "fit notes" issued by GPs has risen by nearly a tenth, with a larger increase for mental and behavioural disorders, research has shown.
The latest available NHS Digital figures show 1.4 million fit notes were issued between July and September 2017, a 9% increase on the 1.3 million issued over the same period in 2016.
The research was carried out by GP magazine Pulse, which also found that many doctors believe the advice written on them is ignored by employers.
It showed a 13.5% rise in fit notes issued for mental and behavioural disorders, while the number of notes that were for five weeks or longer went up slightly from 34.4% to 35.2%.
The Statement of Fitness for Work, also known as the Med3 form or fit note, was introduced in April 2010 across England, Wales and Scotland to enable doctors to provide medical evidence for employers or support a claim for health-related benefits.
A fit note is issued after the first seven days of sickness absence if the doctor assesses that the patient's health affects their fitness for work.
They can decide the patient is "unfit for work" or "may be fit for work subject to the following advice...", with accompanying notes on suggested adjustments or adaptations to the job role or workplace.
Pulse said it has spoken to many GPs who complain about the amount of time the paperwork takes to carry out and find a lot of employers and employees do not understand how fit notes work.
Some patients are also accused of making "inappropriate appointments" to get the notes filled in by their doctor.
Its survey of more than 800 GPs found 21% thought employers did not usually follow the advice set out in the notes.
British Medical Association (BMA) GP committee chairman Dr Richard Vautrey said: "This is yet another indicator showing the workload pressures GPs are facing as they strive to respond to demand from their patients, and in particular the growing number of people living with stress, anxiety and depression.
"Despite this, mental health funding has lagged behind, exacerbating the problem. The vast majority of adults with mental health problems are looked after in primary care, but our own research has shown unacceptably long waiting times to access talking therapies, which can often lead to patients taking longer to recover and further impact being felt in general practice.
"This is why we need more investment in local mental health therapists and IAPT (improving access to psychological therapies) services."