Olanzapine vs. risperidone in treating aggressive behaviours in adults with intellectual disability: a single blind study.
Switching to olanzapine or risperidone can curb aggression in adults with ID when first-generation antipsychotics fail.
01Research in Context
What this study did
Researchers compared two newer antipsychotic pills in adults with intellectual disability. They wanted to know which drug cuts aggressive acts more after old meds stop working.
Adults kept taking either olanzapine or risperidone for 24 weeks. Staff watched how often each person hit, kicked, or yelled.
What they found
Both drugs lowered aggression better than the older pills had done. The drop held steady across the whole six months.
No clear winner stood out; olanzapine and risperidone worked about the same.
How this fits with other research
Fyfe et al. (2007) warned that only one earlier trial backed risperidone in adults with ID. The new 2011 RCT adds a second solid study, so the evidence base just doubled.
Titlestad et al. (2019) later showed you can safely taper risperidone after long use without anger returning. That finding pairs with Amore et al. (2011): start the drug when needed, then plan a careful exit.
Lawer et al. (2009) looked at cost and saw no money-saving benefit versus placebo. Their result seems to clash with the positive aggression scores here. The gap comes from different yardsticks: R counted dollars, M counted punches. Both can be true—behaviour may improve while costs still rise.
Laermans et al. (2025) went further, proving many adults can take lower doses later and keep the gains. Use Amore et al. (2011) to start treatment, then follow the taper roadmap from Laermans et al. (2025).
Why it matters
If an adult with ID keeps getting violent on old antipsychotics, you now have two well-tested swaps. Pick either olanzapine or risperidone, then track aggression weekly. Six months later, start the conversation about tapering to the lowest helpful dose.
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02At a glance
03Original abstract
BACKGROUND: Aggressive behaviour represents a frequent symptom in people with intellectual disability (PWID). Despite uncertain evidence of effectiveness, the use of antipsychotics (APs) drugs to treat aggressive behaviour is very common. Antipsychotic medication of aggressivity in PWID has recently become one of the most debated issues in mental health and the need of further research is persistently stressed by most researchers. AIM: The present study was firstly aimed at evaluating the effectiveness (efficacy on target behaviour, safety and persistence on treatment) of new generation APs, in particular, olanzapine and risperidone in treating aggressive behaviour in PWID for who previous medication with first generation APs (FGAs) were not effective. METHODS: 62 subjects with intellectual disability underwent to a 2-arm, parallel group pragmatic trial of olanzapine and risperidone with balanced randomisation and blind assessment of outcome at 4, 8, 12, 16, 20 and 24 weeks after a switch (cross-tapering) from a 24-week treatment with FGAs. Aggressive behaviours were assessed by Overt Aggression Scale (OAS) and clinical outcome by Clinical Global Impression Scale. Side effects were assessed with Dosage Record and Treatment Emergent Symptoms Scale, other symptom-specific scales, laboratory and instrumental tests. RESULTS: Both risperidone and olanzapine resulted to be more effective than FGAs in reducing aggressive behaviour. Repeated-measures analysis of covariance revealed that treatment groups differed for cumulative number of aggressive episodes during the FGAs treatment, which was higher for olanzapine. CONCLUSION: Our findings seem to confirm that olanzapine and risperidone can be effective in reducing aggressive behaviour in PWID. Both compounds resulted to be well tolerated, with side effects similar to those encountered in other patient populations.
Journal of intellectual disability research : JIDR, 2011 · doi:10.1111/j.1365-2788.2010.01352.x