Controversy surrounds anti-psychotic drugs
Scientists have raised concerns that claims about the benefits of a new generation of drugs for conditions such as schizophrenia may have been exaggerated.
Not only are the new antipsychotic drugs - known as atypicals - thought to be more effective, they have also been associated with fewer side effects.
However, a new study has questioned whether they are actually as relatively side effect free as was thought.
The drugs, which include risperidone, quetiapine, clozapine and olanzapine, have been approved for use by the NHS by the National Institute for Clinical Excellence (NICE).
In a significant number of cases (by no means everyone) atypical drugs can transform lives in a way in which the older drugs have failed
However, they are very expensive, and campaigners are concerned that they have only been made available to a small minority of patients who would benefit.
The latest study has examined concerns that the drugs' reputation for being side effect free is unjustified - largely because initial trials compared them with a particularly potent older generation drug called haloperidol.
A team from Zucker Hillside Hospital in New York lead by Dr Stefan Leucht carried out a comprehensive review of data from 31 studies which involved 2,320 patients.
Of the new generation drugs, only clozapine was associated with fewer neurological side-effects and higher efficacy than low-potency conventional drugs.
And as a group, new-generation drugs were only moderately more efficacious than low-potency conventional antipsychotics.
Dr Leucht said: "If these findings are confirmed by future studies, there would be a good argument for the use of appropriately dosed conventional drugs - such as chlorpromazine - for patients with schizophrenia in settings where new-generation drugs are not generally affordable."
Marjorie Wallace, chief executive of mental health charity SANE, expressed concern that the benefits of the newer drugs was being questioned.
She said: "All drugs, if they are to be effective, will have side effects, but our experience is that for the majority the side effects of the newer drugs are more tolerable, people are more willing to take them and they are therefore more effective.
"In a significant number of cases (by no means everyone) atypical drugs can transform lives in a way in which the older drugs have failed."
Paul Corry, of the charity Rethink, said much more research was needed before a switch away from the newer drugs could be seriously considered.
"People generally prefer the new atypical antipsychotics because they are associated with fewer and less severe side effects.
"All medicines have side-effects of some kind. They tend to be most severe when, as is often the case with medicines for treating psychosis, they are prescribed without the full involvement of the person taking them or above recommended dosage levels."
Anne-Toni Rodgers, NICE corporate affairs director, said older anti-psychotics did work for some people - but not all.
"For many people these traditional medicines control the symptoms of their schizophrenia without side effects, however for others the side effects they experience are so distressing that they may stop taking their medicine which means the symptoms of their schizophrenia can become uncontrolled to the extent that they require hospital care."
The research is published in The Lancet medical journal.