Stress is driving increasing numbers of teachers out of the profession, with some even considering suicide, a teaching union conference heard on Monday.

Delegates at the National Union of Teachers conference in Harrogate heard there had been a "meteoric" rise in work-related stress due to demands to meet government targets.

Research by the Health and Safety Executive in 2000 found teaching to be the most stressful profession, with 41.5% of teachers reporting themselves as "highly stressed".

Sue McMahon, a delegate from Calderdale, West Yorkshire, said: "As a divisional secretary, I have seen a meteoric rise in work-related stress and on more than one occasion have had to support a member who has attempted suicide.

"This … is due to the demands being placed on our members to hit government targets."

She said a "target tsunami" from government is "sweeping away those [teachers] that you are struggling to support".

Laura Fisher from Wakefield told delegates how two weeks into her first job as a teacher, a colleague looked at her and said: "'Go home and drink a bottle of wine and you'll be fine.' I said 'I don't drink', and he said, 'give it six months'.

"That was six years ago. I still don't drink, but I do like chocolate."

The NUT is concerned that an increase in form-filling has driven up teachers' workloads.

The union passed two resolutions, calling for the union to support victims of work stress and for the Health and Safety Executive to intervene in schools where employers do not carry out assessments of the risk of stress.

Christine Blower, general secretary of the NUT, said: "Despite measures to reduce teachers' workload, we still have the unacceptable situation of many classroom teachers, heads and deputies working in excess of 50 hours a week. With no limit to the working week, the long hours continue to take their toll on teachers' health and their lives outside work.

"Much of this time is spent on tasks which have little to do with teaching and learning, but are instead generated by unnecessary bureaucratic procedures which have become the bane of teachers' lives."

Reducing the burden of planning and assessment on teachers would help reduce the workload of school staff, Blower said.

"In too many schools, planning and assessment requirements have become formulaic burdens which simply waste teachers' time."

John Illingworth from Nottingham told delegates the number of stress-related suicides among teachers is "low but significant".

"Stress-related illness is widespread, affecting thousands of teachers each year. It is more likely to end a teacher's career than any other cause," he said.

Peter Harvey – the teacher who was given a community order after beating a 14-year-old pupil with a dumbbell – warned last year that "lots of teachers are ticking time bombs" because of stress in schools.

In an interview with the Mirror, Harvey said: "I know teachers who, because of stress, can't hold a cup of coffee or are too frightened to cross the road."

The Guardian April 2011