Recipient organisationNIHR Maudsley Biomedical Research Centre
NIHR supportRecorded as supported by this research centre
PeriodMar 2025 — Ongoing
In plain English
AI plain-English summary
Clozapine is the most effective antipsychotic for schizophrenia, but it causes excessive drooling that can make patients want to stop taking it. This trial will test whether two existing medications—hyoscine and glycopyrrolate—can reduce that drooling better than a placebo. The problem is that no proven treatment exists for clozapine-induced hypersalivation. Doctors currently prescribe hyoscine based on guesswork, not evidence, and it can cause constipation and problems with attention and concentration. Glycopyrrolate may cause fewer thinking problems, but its side effects are also unclear. Without reliable data, patients cannot make informed choices about whether to tolerate drooling or risk side effects from unproven drugs. If the trial shows that either medication works, patients will have a real treatment option for a side effect that is deeply embarrassing and can lead to hospitalisation if they stop clozapine. If both work, the study will compare side effects and ask patients which they prefer, giving clinicians clear guidance on prescribing. This is a practical, patient-led trial that directly addresses a gap in everyday psychiatric care—no fundamental science, just a head-to-head comparison of two cheap, available drugs against a placebo.
View original technical description
Clozapine is an antipsychotic medication used to help treat the symptoms of schizophrenia and is also sometimes used to treat other mental health conditions. It is the most effective antipsychotic medication for many people and it is important to keep taking it. Clozapine can cause different side effects and people tell us one of the most upsetting is excessive drooling. Doctors call this ‘clozapine-induced hypersalivation’ (CIH or drooling). People with CIH/drooling tell us they often have to wipe the saliva from their mouth during the day and their pillow becomes very wet at night which can sometimes make the skin on their face sore. CIH can be very embarrassing and lead to some patients wanting to stop clozapine treatment. For most patients this is not a good idea as their mental illness is likely to come back and they may need to be admitted to hospital. Currently there is no proven treatment for CIH. The medication usually prescribed is called hyoscine but we don’t know if hyoscine helps although doctors think it might. Hyoscine can cause unpleasant side effects such as bowel problems (constipation) and thinking problems (making attention and concentration worse). Some studies suggest a different medication called glycopyrrolate might be helpful for CIH and may cause fewer thinking problems. But it may still cause other side effects like constipation. Patients have told us that it is important for them to know which medications may improve CIH and what the side effects are so they can make an informed choice about whether or not to take any of these medicines based on their mental illness symptoms and experience of side-effects. Our study will find out if either hyoscine or glycopyrrolate can improve CIH/drooling by comparing patients taking these medications with patients taking a dummy treatment (placebo). If both help reduce CIH/drooling we will compare the two medications to see which one causes fewer side effects and ask which one patients prefer.
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