Mexico City: Transgender identity should no longer be classified as a mental disorder in a World Health Organization list of diseases, according to a study presented in Mexico on Thursday.

Violence and social rejection are the cause of mental distress and impairment among transgender people, not their gender identity, according to the research published in the journal The Lancet Psychiatry.

"If it's not a disease now, then it never was. This should be clear," Eduardo Madrigal, president of the Mexican Association of Psychiatry, said at a news conference.

The field study was conducted between April and August 2014 among 250 transgender adults who were receiving health care services at the Condesa Specialized Clinic in Mexico City.

The group went through an interview which found that 83 percent had experience distress over their gender identity during adolescence.

It is the first in a series of similar studies that will be conducted in Brazil, France, India, Lebanon and South Africa.

The results will be presented at the 11th revision in 2018 of the WHO's International Classification of Diseases, a diagnostic tool for health care providers around the world.

"This reclassification will not only promote discussions for new health policies for the trans community to have better access to health services, but it will also help to reduce the stigma and rejection that they are victims of," said Ana Fresan, one of the study's authors.