Chlorpromazine and Phenobarbital interaction
Chlorpromazine and Phenobarbital: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Chlorpromazine (Chlorpromazine Hydrochloride) label · effective 2026-02-02
Do not use in comatose states or in the presence of large amounts of central nervous system depressants (alcohol, barbiturates, narcotics, etc.).
Because of its CNS depressant effect, chlorpromazine should be used with caution in patients with chronic respiratory disorders such as severe asthma, emphysema and acute respiratory infections, particularly in children (1 to 12 years of age).
Chlorpromazine prolongs and intensifies the action of CNS depressants such as anesthetics, barbiturates and narcotics.
When chlorpromazine is not being administered to reduce requirements of CNS depressants, it is best to stop such depressants before starting chlorpromazine treatment.
Therefore, dosage of anticonvulsants, including barbiturates, should not be reduced if chlorpromazine is started.
From the Phenobarbital (SEZABY) label · effective 2025-12-23
CNS depressants: Closely monitor for sedation and respiratory depression.
Drugs that Prolong the QT Interval : Avoid concomitant use.
CNS Depressants Closely monitor for signs of sedation and respiratory depression with concomitant use of SEZABY with other CNS depressants, including opioids [see Warnings and Precautions (5.1)] .
QT Prolongation SEZABY may prolong the QT interval [see Clinical Pharmacology (12.2)] .
Drugs that Prolong QT Interval SEZABY may prolong the QT interval [see Warnings and Precautions (5.10) and Clinical Pharmacology (12.2)] .
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Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.