Many depictions of mental illness on TV are frightening and misleading, a government-backed report says.
The study, commissioned by the Department of Health, found nearly half of all mentally ill characters were portrayed as dangerous to others.
Its author said the "axe-wielding maniac" stereotype should be ditched.
Mental health charity Mind said progress had been made in dramas such as EastEnders and Shameless, but more improvement was needed.
Television and films have been using the "madman" as a dramatic device for decades, but in reality, the vast majority of people with mental health problems pose no risk to others.
The Glasgow Media Group, working on behalf of a Department of Health campaign called "Shift", examined dozens of popular dramas and comedies to see how mental illness was presented to the viewer.
It found that most references to mentally ill people were insulting, examples being the terms "crackpot", "basket case" or "a sad little psycho".
In addition, 45% of storylines involving people with mental health problems found them posing some kind of risk to others.
Recent examples were a character in ITV soap Emmerdale who drugs the village vicar, or a schizophrenic killer in the popular US show CSI: Miami.
Even in BBC One soap EastEnders, which was praised for a realistic portrayal of bipolar disorder with character Stacey Slater, had the same character eventually commit murder.
Professor Greg Philo, who led the research, said: "Fictional film characters like Hitchcock's Norman Bates in 'Psycho' have long established the idea of the 'mentally ill' as crazed and dangerous in the public mind; television has been doing the same thing for decades.
"Great progress has been made in recent years, but we've some way to go before we see more of the everyday realities of living with a mental health problem properly represented and stereotypes like the axe-wielding maniac take a back seat."
Almost half of programmes did offer sympathetic portrayals, although these often showed the character as a "tragic victim", the researchers said.
The depiction of another character with bipolar disorder on Channel 4's Shameless won praise for accuracy and sensitivity.
Paul Farmer, the chief executive of Mind, said that improvements over the past decade had been due to the willingness of scriptwriters and programme producers to involve people with personal experience of mental health problems while carrying out research.
He said: "It is also clear, however, that there is still much work to be done until we are at a stage where accurate depictions are the norm rather than the exception.
"I hope this report will encourage programme makers to follow these examples of good practice to create accurate, well-rounded characters that can improve perceptions of mental health."