A case of phenobarbital exacerbation of a preexisting maladaptive behavior partially suppressed by chlorpromazine and misinterpreted as chlorpromazine efficacy.
Phenobarbital can secretly worsen aggression; removing it first can let you cut antipsychotics safely.
01Research in Context
What this study did
A doctor watched one adult with developmental delay. The man took phenobarbital for seizures and chlorpromazine for aggression. Staff thought chlorpromazine kept him calm. The doctor slowly stopped both drugs. He wanted to see what really caused the hitting and head-banging.
What they found
When phenobarbital left first, the calm stayed. Chlorpromazine could then be cut with no return of aggression or self-injury. The seizure drug, not the antipsychotic, had been driving the behavior all along.
How this fits with other research
Frank‐Crawford et al. (2026) give you a tool. Their augmented competing-stimulus test finds safe items that cut self-injury by 80%. You can use it after you remove the hidden drug cause.
Moon et al. (2024) show a fix for the same pitfall. A pharmacist checked 97 adults with IDD and made 308 drug changes. That service could have spotted the phenobarbital problem early.
Bigby et al. (2009) back the warning. They audited charts and saw many anticonvulsant scripts lacked clear reasons. Poor notes hide side-effects just like in this case.
Why it matters
Before you add or keep a psychotropic, ask if another drug is the real trouble. A short medication review can save months of needless sedation. Try a simple rule: when taper fails, re-check every prescription for hidden drivers. Your client may leave with fewer meds and zero extra behavior.
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02At a glance
03Original abstract
An adult female with developmental disability was prescribed chlorpromazine for the target behaviors of aggression and self-injurious behavior (SIB), and she was prescribed phenobarbital for seizures. Upon a chlorpromazine minimal effective dose reduction, target behaviors increased and dosage was returned to prior levels with the conclusion that chlorpromazine was controlling the target behaviors. Upon subsequent reduction and discontinuation of phenobarbital, however, chlorpromazine was able to be reduced with no increase in target behaviors. Ten years of behavioral data are presented to support the hypothesis that phenobarbital was exacerbating maladaptive behaviors. Given tardive dyskinesia (TD), clinicians and interdisciplinary teams should remain alert to the following client profile: (1) prescribed phenobarbital (or primidone), (2) prescribed neuroleptics, especially at high dosages, to control maladaptive behaviors, (3) failure of neuroleptic gradual minimal effective dose attempts, and (4) possible presence of behavioral procedures, especially intrusive procedures, to control maladaptive behaviors. This profile should trigger a "red flag" as to the possibility of phenobarbital behavioral side effects or exacerbation of preexisting maladaptive behaviors.
Research in developmental disabilities, 1992 · doi:10.1016/0891-4222(92)90012-u