Acetaminophen and codeine and Isoniazid interaction
Acetaminophen and codeine and Isoniazid: 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 Acetaminophen and codeine (ACETAMINOPHEN AND CODEINE PHOSPHATE) label · effective 2026-01-22
Interactions with Drugs Affecting Cytochrome P450 Isoenzymes The effects of concomitant use or discontinuation of cytochrome P450 3A4 inducers, 3A4 inhibitors, or 2D6 inhibitors with codeine are complex.
Use of cytochrome P450 3A4 inducers, 3A4 inhibitors, or 2D6 inhibitors with acetaminophen and codeine phosphate tablets requires careful consideration of the effects on the parent drug, codeine, and the active metabolite, morphine ( see WARNINGS and PRECAUTIONS, Drug Interactions ).
…respiratory depression ( see WARNINGS ). acute or severe bronchial asthma in an unmonitored setting or in the absence of resuscitative equipment ( see WARNINGS ). concurrent use of monoamine oxidase inhibitors (MAOIs) or use of MAOIs within the last 14 days ( see WARNINGS ). known or suspected gastrointestinal obstruction, including paralytic ileus ( see WARNINGS…
Acetaminophen and codeine phosphate tablets should not be used in patients taking MAOIs or within 14 days of stopping such treatment.
Cytochrome P450 3A4 Interaction The concomitant use of acetaminophen and codeine phosphate tablets with all cytochrome P450 3A4 inhibitors, such as macrolide antibiotics (e.g., erythromycin), azole-antifungal agents (e.g., ketoconazole), and protease inhibitors (e.g., ritonavir) or discontinuation of a cytochrome P450 3A4 inducer such as rifampin, carbamazepine,…
From the Isoniazid label · effective 2026-04-27
Acetaminophen A report of severe acetaminophen toxicity was reported in a patient receiving isoniazid.
It is believed that the toxicity may have resulted from a previously unrecognized interaction between isoniazid and acetaminophen and a molecular basis for this interaction has been proposed.
Studies have demonstrated that pretreatment with isoniazid potentiates acetaminophen hepatotoxicity in rats 1,2 .
Furthermore it has been proposed that isoniazid resulted in induction of P-450IIE1 in the patient's liver which, in turn, resulted in a greater proportion of the ingested acetaminophen being converted to the toxic metabolites.
Taking more than these two? Interactions stack. Check your whole list at once; it stays in your browser.
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.