A specially-designed drink can enhance the effectiveness of schizophrenia drugs, scientists say.
One in 100 will be diagnosed with schizophrenia during their lifetime
The drink, Tyrodep, is high in amino acids and helps control levels of the chemicals in the brain which are thought to underlie the illness.
Oxford University researchers, who developed the drink, said it helped to alleviate side effects associated with the medication.
Mental health charities called the research "an important breakthrough".
Over one million people in the UK are affected by mania or schizophrenia and many control their symptoms with antipsychotic drugs.
But the drugs can cause side effects including Parkinson's disease-like symptoms such as stiffness and shakiness, a permanent movement of the mouth and tongue, weight gain and sexual problems.
The amino acids in the drink reduce levels of dopamine. Excess levels of this brain chemical are thought to cause many of the symptoms of manic conditions.
Professor Guy Goodwin, who led research which was funded by the Wellcome Trust, said: "Conventional antipsychotics can be used effectively in managing mental illnesses like schizophrenia and mania. However, the side effects can understandably cause some patients to become cautious in taking them.
"The drink we've developed, when taken alongside medication, has proven to be a real step forward.
"It may be both more acceptable to patients and help to reduce the unwanted side effects people get from their treatment.
"Hopefully it will allow them to get on with their lives."
He added: "Conventional medication acts as a 'brake' on dopamine production. But it can actually lead to more of the chemical being produced as the system tries to overcome that brake."
Professor Goodwin said it may be possible to control manic conditions using the drink alone, but much more research was needed before that treatment method could be recommended to patients.
Marjorie Wallace, chief executive of mental health charity Sane, said the drink could benefit many people.
"The frustration that so many individuals with schizophrenia or manic depression, and their families, experience is that often treatment is limited to medications which mostly have debilitating side effects.
"If this product proves as successful as its early results suggest, it could be an important breakthrough in encouraging people to work with their medication and lead more positive lives."
The Oxford researchers now hope to develop the drink and make it widely available to patients.