Side-effects of antidepressants, including thoughts of suicide, sexual difficulties and emotional numbness, may be more widespread than previously thought, according to a recent study.

Researchers from the University of Liverpool found that large numbers of people - more than half in some cases - reporting on psychological problems due to their medication, which has led to growing concerns about the scale of the problem of over-prescription of these drugs.

"While the biological side-effects of antidepressants, such as weight gain and nausea, are well documented, the psychological and interpersonal effects have been largely ignored or denied. They appear to be alarmingly common," Professor John Reed, psychologist and lead researcher, said in a statement.

Reed said the medicalization of sadness and distress has reached bizarre levels; one in ten people in some countries are now prescribed antidepressants each year.

For the study, researchers surveyed 1, 829 people who had been prescribed antidepressants. The study asked about twenty adverse effects of the drugs. The study was carried out in New Zealand and all of the participants had been on antidepressants in the last five years. The survey factored in people's levels of depression and asked them to report on how they had felt while taking the medication.

They found that more than half people aged 18 to 25 in the study reported suicidal feelings. In the total sampling, 62 percent of people suffered from sexual difficulties, 60 percent reported feeling emotionally numb, and 42 percent said they felt a reduction in positive feelings. Participants also said they started caring less about others after taking antidepressants, according to a press release.

However, despite the reported side-effects, 82 percent of those surveyed said that the drugs helped alleviate their depression.

"Effects such as feeling emotionally numb and caring less about other people are of major concern. Our study also found that people are not being told about this when prescribed the drugs," Reed said. "Our finding that over a third of respondents reported suicidality 'as a result of taking the antidepressants' suggests that earlier studies may have underestimated the problem."