An overhaul of A-levels and GCSEs has had a major effect on students' mental health, according to a union.
Many secondary school teachers believe the new qualifications have increased pressure on youngsters to do well and led to more anxiety and stress, a National Education Union poll indicates.
It also suggests some think that the content of the new courses has become more demanding and this has had an impact on their workload.
Major reforms that began under the coalition government have seen GCSEs toughened up, with exams now taken at the end of the two-year courses rather than throughout, and less coursework. The traditional A*-G grading system has been replaced by 9-1 grades.
At A-level, there are also no longer exams throughout, and AS-levels, traditionally taken by students after one year of study, have been hived off to form a standalone qualification.
The poll, which questioned 656 members working in English secondary schools, found 89% believe that assessment method for new GCSE courses is worse for students' mental health than before, whilst 66% said the same for A-levels.
One teacher told the union: "A lot more anxiety and stress with more GCSE exams and everything being a memory test," while another said there is "huge increase in pressure to succeed, increase in workload and revision for students, feeling of inferiority due to more difficult content, constant feeling of failure".
A third said: "More cases of students exhibiting extreme anxiety. More struggling to cope with the demands of multiple practical courses. Many struggling with course content and the volume and depth of study required."
The survey also found that at GCSE, 78% said there has been a significant increase in the level of demand of the subject they teach, while one 1% said there had been a significant decrease.
For A-level, 41% said there had been a significant increase in demand and 1% said there had been a significant decrease.
In addition, 63% said there had been a significant increase in their workload at GCSE, with 2% saying there had been a significant decrease - while at A-level the figures were 48% significant increase and 0% significant decrease.
Nansi Ellis, NEU assistant general secretary for policy, said: "Hasty implementation of the new GCSEs and A-levels - with changes to content, the level of difficulty and grading - have caused huge difficulties for students and staff and put them under excessive pressure.
"It is worrying that so many students are suffering from stress and anxiety, particularly at GCSE level, because of changes to the way in which they are assessed.
"With over eight-in-10 teachers reporting that the new GCSEs and A-levels have increased their workload, it is no wonder there is a recruitment and retention crisis."
A Department for Education spokeswoman said: "The government's new gold-standard GCSEs and A-levels are the culmination of a programme of curriculum and qualifications reform over the last seven years after employers told us they were failing to prepare young people for the future.
"The new qualifications will help young people compete with the best in the world and deliver the skills businesses tell us they need.
"We know exam season can be a time of heightened emotions for pupils who want to do their best. While testing has always been an important part of education, it should never be at the expense of a young person's wellbeing.
"We trust schools to make sure that pupils preparing for exams get the help and support that they need, when they need it, working with parents to do this."
* The survey questioned 656 secondary school teachers in England between June 27 and July 11.