Fentanyl and Isoniazid interaction
Fentanyl and Isoniazid: the Fentanyl prescribing label 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 Fentanyl (FENTANYL CITRATE) label · effective 2026-04-07
• Concomitant use with CYP3A4 inhibitors (or discontinuation of CYP3A4 inducers) can result in a fatal overdose of fentanyl.
Cytochrome P450 3A4 Interaction The concomitant use of Fentanyl Citrate Injection with all cytochrome P450 3A4 inhibitors may result in an increase in fentanyl plasma concentrations, which could increase or prolong adverse reactions and may cause potentially fatal respiratory depression.
Monitor patients receiving Fentanyl Citrate Injection and any CYP3A4 inhibitor or inducer [see Warnings and Precautions (5.4) , Drug Interactions (7) , Clinical Pharmacology (12.3) ] .
Monoamine Oxidase Inhibitors Clinical Impact: MAOI interactions with opioids may manifest as serotonin syndrome [see Warnings and Precautions (5.8) ] or opioid toxicity (e.g., respiratory depression, coma) [see Warnings and Precautions (5.2) ].
Intervention: The use of Fentanyl Citrate Injection is not recommended for patients taking MAOIs or within 14 days of stopping such treatment.
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.