Risperidone, an antipsychotic medication used to treat schizophrenia, bipolar disorder, and irritability in autism, causes side effects in most people who take it. The most common are drowsiness, weight gain, and movement-related problems. Some effects are mild and temporary, while others, particularly hormonal and metabolic changes, can develop gradually and persist with long-term use.
Drowsiness, Fatigue, and Sleep Changes
Feeling sleepy or sedated is the single most reported side effect. In clinical trials of children treated for autism-related irritability, 49% experienced drowsiness and 29% experienced sedation, compared to 18% and 3% on placebo. In adults with schizophrenia, drowsiness affected about 7% at standard doses. Fatigue is also prominent: in pediatric bipolar trials, 30% of those on higher doses reported fatigue versus just 3% on placebo.
Insomnia is paradoxically common too. In adult schizophrenia trials, about 32% of people taking risperidone at standard doses reported trouble sleeping, though the placebo group also had a high rate (27%), reflecting the underlying condition. Anxiety affected roughly 16% of adults in those same trials.
Weight Gain and Metabolic Changes
Weight gain is one of the most clinically significant side effects. In a study of young children with autism, those taking risperidone for about 23 weeks gained an average of 5.4 kilograms (nearly 12 pounds). The prevalence of overweight and obesity is significantly higher in children and adolescents on risperidone compared to the general population, making this a particular concern for younger patients on long-term treatment.
The weight gain isn’t just cosmetic. Within the first 16 weeks of treatment, researchers have documented meaningful increases in blood sugar, insulin levels, and a marker of long-term blood sugar control. Insulin resistance, a precursor to type 2 diabetes, worsened significantly. In one study, 12 additional children met criteria for metabolic syndrome by week 16 who hadn’t met them at the start. Increased appetite drives much of this: 47% of children in autism trials reported heightened hunger.
Movement Problems
Risperidone can cause a range of involuntary movement issues that doctors group under the term “extrapyramidal symptoms.” These include stiffness and slowed movement (parkinsonism), an uncomfortable inner restlessness that makes you feel like you can’t sit still (akathisia), and tremor.
Parkinsonism affected 14% of adults on standard doses in schizophrenia trials and climbed to 17% at higher doses, compared to 8% on placebo. In children, the rates were higher: 28% of adolescents with schizophrenia on higher doses developed parkinsonism. Akathisia affected about 10% of adults regardless of dose. Tremor hit 11-12% of children in several trials.
These movement effects tend to be dose-dependent. Higher doses consistently produced more parkinsonism across every patient group studied. With long-term use, there is also a risk of tardive dyskinesia, a condition involving repetitive, involuntary movements of the face, tongue, or limbs that can sometimes be irreversible. One study in elderly patients estimated the incidence at roughly 2.6% to 4.5% per year of treatment. Compared to older antipsychotics, risperidone carries a lower risk, but the risk is not zero.
Hormonal Effects and Prolactin Elevation
Risperidone raises prolactin levels more than almost any other atypical antipsychotic. It does this by blocking dopamine receptors in the part of the brain that normally keeps prolactin in check. Without that brake, prolactin levels climb, sometimes substantially.
The consequences differ by sex. Women may experience irregular or missed periods, breast discharge (galactorrhea), decreased sex drive, and even fertility problems, sometimes despite seemingly regular cycles. Men may notice reduced libido, difficulty with erections, and rarely, breast tissue enlargement or breast discharge.
Sexual Side Effects
Sexual dysfunction on risperidone is common and likely underreported, since many people don’t bring it up unless asked. In prospective studies, up to 60% of patients reported reduced libido. Erectile dysfunction affected between 31% and 46% of men across multiple studies, depending on how it was measured. A six-month observational study found that 35.5% of people on risperidone experienced loss of libido. These numbers are high enough that sexual side effects should be considered a probable rather than occasional consequence of treatment.
Digestive Side Effects
Nausea, constipation, dry mouth, abdominal pain, and vomiting all appear in clinical trial data. In pediatric bipolar trials, nausea affected 16% of those on lower doses and 13% on higher doses, versus 7% on placebo. Upper abdominal pain followed a similar pattern. Drooling (excess saliva production) is more common in children, affecting 16% in autism trials. Nausea and vomiting were among the side effects most likely to cause people to stop taking the medication entirely.
How Dose Affects Side Effects
Many of risperidone’s side effects follow a dose-response pattern, but not always in the direction you’d expect. Parkinsonism consistently worsens at higher doses: 16% at 1-3 mg versus 28% at 4-6 mg in adolescent schizophrenia trials. Fatigue jumped from 18% to 30% in pediatric bipolar patients moving from the lower to higher dose range. Dizziness showed a similar trend in several groups.
Drowsiness, interestingly, was sometimes more common at lower doses in adult trials, possibly because higher-dose groups had more time to develop tolerance or because severely ill patients on higher doses perceived sedation differently. The practical takeaway: starting at a low dose and increasing slowly gives your body more time to adjust, but certain side effects like movement problems and metabolic changes tend to accumulate with both dose and duration.
Side Effects in Children
Children and adolescents generally experience the same side effects as adults but at higher rates. In autism trials, the numbers are striking: nearly half experienced increased appetite and drowsiness, and over 40% reported fatigue. Weight gain is a particular concern because childhood obesity carries long-term health consequences, and children on extended risperidone treatment face an elevated risk of becoming overweight or obese compared to their peers.
Sedation can interfere with school performance and daily functioning, especially in the first weeks. Movement side effects also tend to be more common in pediatric populations, with parkinsonism and tremor each affecting over 10% in most trials.
Risks in Older Adults
Risperidone carries an FDA black box warning, the most serious type of safety alert, regarding use in elderly patients with dementia-related psychosis. These patients face an increased risk of death when treated with antipsychotic medications, including risperidone. The medication is not approved for this use. Older adults are also more vulnerable to movement disorders, falls from dizziness or sedation, and the metabolic effects described above.
Rare but Serious Reactions
Neuroleptic malignant syndrome is a rare, life-threatening reaction that can occur with risperidone or any antipsychotic. It causes high fever, severe muscle rigidity, confusion, and unstable blood pressure and heart rate. This is a medical emergency requiring immediate hospital treatment. It can happen at any point during treatment, including shortly after starting or after a dose increase.
How Risperidone Compares
Among atypical antipsychotics, risperidone stands out for its relatively high rates of prolactin elevation and movement-related side effects. In head-to-head trials, risperidone produced more parkinsonism, akathisia, and prolactin changes than quetiapine. Quetiapine, by contrast, caused more sedation, dizziness, constipation, and rapid heart rate. Both medications caused weight gain. As a class, atypical antipsychotics carry less risk of movement disorders than older antipsychotics but tend to cause more metabolic side effects.