A total of 25% of people with schizophrenia say they have stopped taking medication because of adverse side effects, research has found.
Schizophrenia pills can have side effects
The charity Sane said this was leading to an increase in relapse rates and hospital re-admissions.
Its survey found that 62% of respondents had not been told about side effects, including weight gain, drowsiness and restlessness.
The charity is calling for better communication by health workers.
The survey found that three-quarters of patients suffer from side effects, which can put them at greater risk of serious conditions such as diabetes and cardiovascular disease.
Schizophrenia is the most common major psychiatric disorder and affects around one in 100 people in the UK.
The condition is associated with a shorter life expectancy, although this is thought to be due to a number of factors, including reduced socio-economic status.
The findings of the latest study echo previous research which found that one in 10 psychiatrists never proactively discussed long-term health risks associated with some treatments.
Marjorie Wallace, chief executive of Sane, said: "It is appalling that so many patients are not being given information vital to understanding the impact of their treatment and in turn their ability to make decisions and help in their own recovery.
Newer 'atypical' antipsychotic medications have been shown to treat schizophrenia effectively
However, they can cause side effects, including abdominal weight gain, reduced HDL (good) cholesterol, and raised blood pressure
These may substantially increase the risk of developing conditions such as diabetes and cardiovascular disease
"Without up-to-date and relevant information, patient choice, the cornerstone of the government's health strategy, will continue to be an empty offer."
Mike Launer, a consultant psychiatrist at the Lamont Clinic, Burnley, said: "In prescribing a treatment, psychiatrists have to strike a balance between efficacy and severity of side effects.
"There is a range of drugs available to help people manage the symptoms of schizophrenia, and not all of them are associated with the typical side effects such as weight gain.
"It is important that we as psychiatrists spend the time outlining the medication options available, listen to patients' needs, and offer them a choice, so they are more in control of their disease."