This information is for people who have a child with autism. It tells you about risperidone, a treatment used for autism. It is based on the best and most up-to-date research.
Does it work?
Yes. Children with autism who take risperidone are likely to be less irritable. This drug works as a short-term treatment for children who have tantrums, fight, or hurt themselves.
But risperidone can cause side effects. These include putting on weight, having shaking you can't control (called tremors), and feeling sleepy.
In the UK, only specialists such as child psychiatrists and paediatricians prescribe risperidone for children with autism.
What is it?
Risperidone is an antipsychotic drug. It's usually used to treat mental health problems such as schizophrenia. But some specialists may prescribe it for children with autism if they think it might help.
Risperidone is a newer type of antipsychotic drug. It may have fewer side effects than older drugs of this kind.
One brand name is Risperdal. It comes as tablets, a liquid, or injections.
How can it help?
Taking risperidone reduces symptoms of autism in about 7 in 10 children who have tantrums, fight, or hurt themselves.  The drug can also help if your child is very irritable or hyperactive.
One summary of the evidence said risperidone helped children with autism to: 
Be less irritable
Be less likely to withdraw socially (for example, not talking or interacting with people around them)
Reduce the amount of time they spent repeating words, phrases, or actions.
How does it work?
Risperidone works by calming down activity in your brain. It does this by blocking certain chemicals called neurotransmitters. These chemicals help signals travel between nerve cells. Risperidone blocks the ones called serotonin and dopamine.
Your child may have symptoms such as having tantrums, fighting, and trying to hurt themselves, because there is too much serotonin or dopamine in their brain. So blocking these chemicals might help.
Can it be harmful?
Yes. Risperidone may make your child put on weight. In one study, children taking the drug gained on average 2.7 kilograms (about 6 pounds) over eight weeks.  Children who took a dummy treatment (a placebo) for comparison gained only 0.8 kilograms (about 2 pounds).
Children taking risperidone can also have tremors.  That means they have shaking they can't control. And the drug can make your child sleepy too. One study found that more than 7 in 10 children taking risperidone got sleepy.  Your doctor may suggest your child take this medicine in the afternoon rather than in the morning. That way, your child's school day won't be so affected if they get drowsy. 
Risperidone can also make your child's blood pressure go up a bit and make their heart beat faster.  About 1 in 10 children who take risperidone get a fast heartbeat.