What risperidone 0.5 mg (sold as Sizodone) does — and does not do — for autistic children

Published 14 September 2026 · 3 min read

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Risperidone is a prescription medicine, and Sizodone is one brand of it. A large review of 41 studies found it reliably eased tantrums, aggression and self-injury in autistic children aged 2 to 17, along with overactive behavior, low energy, out-of-place speech and repeated movements, over both short and longer periods. It was also reliably linked with weight gain and a bigger waist. No study tested the 0.5 mg dose or the Sizodone brand on its own; 0.5 mg is simply a common starting or low dose.

What this research found

A large review combined the results of 41 studies. Risperidone improved all five areas of behavior the studies measured. Children did better than before they started, and better than children given a placebo, a dummy pill that looks the same. The five areas were irritability (tantrums, aggression and hurting themselves), overactive behavior, low energy and withdrawal, speech that is out of place, and repeated movements or actions.
The drop in irritability grew larger the longer children took the medicine. The gains for out-of-place speech, low energy and repeated movements were strongest in the first eight weeks.
One trial led the FDA, the US medicines regulator, to approve risperidone for this use. In it, tantrums, aggression and self-injury went down by 57% on risperidone, compared with 14% on the placebo. About 70% of the children who were helped were still doing better six months later.
Risperidone was consistently linked with weight gain and a bigger waist. In earlier trials, children gained around 6 pounds in eight weeks. Other side effects included drowsiness, changes in hormones and, rarely, movements the child cannot control.
Doctors quoted in news reporting describe the medicine as easing distress and explosive behavior, not autism itself. It is not a cure. It does not change the core features of autism, such as how a child connects and communicates.

What this means for caregivers

If irritability, aggression or self-injury is the problem, this is one of the medicine options with the stronger evidence behind it. The change often shows within weeks rather than months.
It is not a treatment for autism. Your child's needs around social communication, and their need for therapy, do not go away. But calmer behavior can make therapy and school possible in a way they were not before.
The appetite and weight effect is predictable enough to plan for. At the start, ask the prescriber how your child's weight, waist size and blood tests will be tracked, and how often. The blood tests check how the body is handling sugar and fats.
A 0.5 mg tablet is usually a starting dose or a low dose. Specialists quoted here favor the lowest dose that works, with regular reviews of whether it is still needed.

Important caveats

This summary is about risperidone, the medicine itself. Sizodone is one brand of it. No study here tested that brand, or the 0.5 mg dose, on its own. In the trials, the dose was set by the child's weight.
More than half of the combined studies were open-label, meaning the families and doctors knew who was taking the medicine. And 19 studies were judged at high risk of bias, meaning the way they were set up could have tilted the results. So it is clearer that risperidone helps than how much it helps.
Most of the evidence covers 8 to 24 weeks. What happens over years, to growth, to how the body handles food and energy, and to thinking skills, has been studied much less.
Behavior problems tend to come back when the medicine is stopped. And a meaningful minority of children do not respond at all.
Never start, stop, change or split a dose on your own. Risperidone needs a prescriber keeping watch over your particular child.

The science behind it

This part is written for researchers, so it gets technical. Reading it anyway is what researchers do: checking how a finding was reached, not just what it says. It’s slow going at first and gets easier after your first few articles. Skipping it is fine too.

A meta-analysis of 41 studies found risperidone consistently reduced irritability, hyperactivity, lethargy, inappropriate speech and stereotypic behavior in autistic children aged 2 to 17, over both short and longer periods. It also found a consistent link with weight gain and increased waist circumference. No study looked at the 0.5 mg dose or the Sizodone brand in isolation — 0.5 mg is simply a common starting or low maintenance dose.

At a glance

Sample size: 41 studies pooled from 2,459 screened articles; participants aged 2-17, mean age 8.1 years, 78% male
Demographics: Autistic children and adolescents aged 2-17 (mean 8.13 ± 2.68 years), 78.28% male, across open-label, double-blind and cross-sectional studies
Key outcome: Risperidone reduced irritability and the other four ABC domains versus both baseline and placebo, short and long term; the earlier RUPP randomized trial found a 57% reduction in tantrums, aggression and self-injury versus 14% on placebo. Weight gain and increased waist circumference were consistently associated with use.
Methodology: PRISMA-registered systematic review and meta-analysis of 41 risperidone studies in autism, pooling change on the five Aberrant Behavior Checklist subscales plus weight and waist circumference, with Jadad quality scoring and Cochrane risk-of-bias assessment. Supporting sources include a systematic review of risperidone's effects on cognition and reporting on the landmark RUPP trial.
Researchers: A. M. Pereira, B. J. M. Silva, B. C. Araújo, J. M. D. Almeida
Institutes: Current Neuropharmacology (PMC8206457), PROSPERO registration CRD42019122316

Limitations:

No study isolated the 0.5 mg dose or the Sizodone brand; trial doses were set by body weight and typically ranged higher, so these results describe risperidone in general
24 of the 41 pooled studies were open-label rather than blinded, and 19 were judged to carry a high risk of bias, mostly from weak randomization
Most follow-up ran only 8 to 24 weeks, so effects and harms beyond a few months are thinly evidenced
Cognitive effects were studied only in small, short trials and remain unresolved
Benefits generally fade when the medicine is stopped, and not every child responds

About this research

The main source is a PROSPERO-registered systematic review and meta-analysis (CRD42019122316) that screened 2,459 articles and pooled 41 studies of risperidone in autistic people aged 2 to 17, following PRISMA and assessing quality with the Jadad scale and the Cochrane Risk of Bias Tool. It is supported by a systematic review of risperidone's effect on cognition and by reporting on the RUPP randomized controlled trial that underpinned the drug's approval. The evidence base is genuinely large, but weighted towards short, open-label studies with known randomization weaknesses.

The research in its own terms. The findings above are written without the names of the scales and outcomes. Here they are, so you can match them to the papers:

Outcome measure: the five subscales of the Aberrant Behavior Checklist (ABC): irritability, hyperactivity, lethargy, inappropriate speech and stereotypic behavior, each reduced compared with both baseline and placebo.
Time course: the irritability reduction was larger with longer use; gains for inappropriate speech, lethargy and stereotypic behavior were strongest in the first eight weeks.
RUPP trial (the basis for FDA approval): a 57% reduction in tantrums, aggression and self-injury on risperidone versus 14% on placebo; roughly 70% of responders were still improved six months later.
Adverse effects: weight gain and increased waist circumference (around 6 pounds in eight weeks in earlier trials), drowsiness, hormonal changes and, rarely, involuntary movements. Prescribers are asked how weight, waist measurement and metabolic bloods will be monitored.
Bias: 24 of the 41 studies were open-label rather than blinded; 19 were at high risk of bias, mostly from weak randomization. Long-term effects on growth, metabolism and cognition are less well studied.

Sources

Effects of Risperidone in Autistic Children and Young Adults: A Systematic Review and Meta-Analysis — Current Neuropharmacology, PMC8206457
The Effects of Risperidone on Cognition in People With Autism Spectrum Disorder: A Systematic Review — Cureus, PMC10507658
Risperidone use in children with autism carries heavy risks — Emily Anthes, 2014, The Transmitter (Spectrum)