CYP450 interaction checker
Add two or more medications. The tool cross-checks each pair against the CYP450 reference table used in our clinician guide and shows every substrate that meets an inhibitor or inducer on your list. Same data, same wording, no personalization.
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Reference lookup
Add at least two medications to see cross-checked reference data.
Reference data current as of June 8, 2026. Sources: FDA prescribing information (via DailyMed), Flockhart Drug Interactions Table (Indiana University), CPIC guidelines, and peer-reviewed literature summarized in the clinician CYP450 guide.
How to read this
Every row shows one substrate on your list meeting one inhibitor or inducer on your list at the same enzyme. The clinical note quotes the reference guide word for word. Nothing in the result is a recommendation to prescribe, adjust, or avoid a medication. It's the same information you'd get from the FDA label, restructured for cross-checking. Every decision belongs with the licensed clinician who knows the patient.
If a medication you use isn't listed, it hasn't been added to the reference dataset yet. That's a gap to fix, not a signal the medication is safe to combine.
About this tool
CYP450 enzymes metabolize the majority of psychiatric medications. When two drugs share a pathway and one of them is an inhibitor or inducer of the shared enzyme, blood levels of the other drug drift up or down. The clinically important pairs are the ones where the drift is large enough to change efficacy (subtherapeutic levels) or safety (toxic levels). This tool exists to make those pairs visible at the point of prescribing.
The five enzymes most relevant to psychiatric prescribing are CYP2D6 (metabolizes many antipsychotics, most TCAs, atomoxetine, opioid analgesics, and dextromethorphan; strongly inhibited by fluoxetine, paroxetine, and bupropion), CYP3A4 (metabolizes many benzodiazepines, quetiapine, lurasidone, buspirone, aripiprazole, cariprazine, ziprasidone; inhibited by fluvoxamine, nefazodone, macrolides, azoles, ritonavir, and grapefruit; induced by carbamazepine, phenytoin, rifampin, and St. John's wort), CYP1A2 (metabolizes clozapine, olanzapine, duloxetine, caffeine, theophylline; strongly inhibited by fluvoxamine and ciprofloxacin; induced by smoking), CYP2C9 (metabolizes warfarin, NSAIDs, phenytoin), and CYP2C19 (metabolizes citalopram, escitalopram, sertraline partially, diazepam, clopidogrel; inhibited by fluvoxamine and fluoxetine).
The tool cross-references entered drugs against the same reference data used in the clinician CYP450 interactions guide. Every result shows the enzyme involved, whether each drug is a substrate, inhibitor, or inducer, the potency classification (strong, moderate, weak), and a verbatim note pulled from the reference. Sources include the Flockhart Table of Drug Interactions (Indiana University), FDA drug labeling via DailyMed, and CPIC guidelines. No patient-level information is entered or stored. The tool runs entirely in the browser and no data leaves your device.
This is a reference lookup for clinicians and clinical trainees. It is not a substitute for reviewing FDA labeling, obtaining a therapeutic drug level when clinically indicated, or considering pharmacogenetic testing in patients with unexplained response failure. For a fuller discussion of how CYP genetics interact with prescribing decisions, see the CYP450 interactions guide.
Common questions
- What is a CYP450 interaction checker?
A CYP450 interaction checker is a lookup tool that shows how two or more medications share cytochrome P450 metabolic pathways. When one drug inhibits or induces the enzyme that metabolizes another, blood levels of the second drug rise or fall, sometimes into a range that changes efficacy or toxicity. The tool cross-checks user-entered drugs against a reference table of substrate, inhibitor, and inducer roles for the five most common enzymes in psychiatric prescribing: CYP2D6, CYP3A4, CYP1A2, CYP2C9, and CYP2C19.
- Which drugs are the strongest CYP2D6 inhibitors in psychiatry?
Fluoxetine, paroxetine, and bupropion are the strongest CYP2D6 inhibitors used routinely in psychiatric practice. Duloxetine is a moderate inhibitor. Any of these can raise blood levels of 2D6 substrates like risperidone, aripiprazole, atomoxetine, tricyclics, codeine, tramadol, and dextromethorphan. The clinical implication is that combining a strong 2D6 inhibitor with a 2D6 substrate often needs a dose reduction on the substrate side, especially in patients who are already CYP2D6 intermediate or poor metabolizers.
- What is the classic clozapine and fluvoxamine interaction?
Fluvoxamine is a strong CYP1A2 inhibitor. Clozapine is a CYP1A2 substrate. Combining them can raise clozapine levels several-fold and precipitate sedation, hypotension, seizures, or agranulocytosis if unrecognized. The interaction is sometimes used deliberately in refractory schizophrenia to boost sub-therapeutic clozapine levels, but only with close TDM. Outside that specific scenario, this pair should trigger a dose review.
- Does grapefruit interact with psychiatric medications?
Grapefruit is a moderate CYP3A4 inhibitor. Psychiatric drugs that are 3A4 substrates and clinically affected by grapefruit include buspirone, quetiapine, lurasidone, ziprasidone, cariprazine, carbamazepine (partially), and some benzodiazepines (midazolam, triazolam, alprazolam to a lesser extent). Buspirone and lurasidone are the most affected: grapefruit can raise levels three to seven-fold. Standard advice is to avoid grapefruit while on these drugs.
- Do smoking status and caffeine affect CYP levels?
Smoking induces CYP1A2. Smokers metabolize 1A2 substrates like clozapine, olanzapine, duloxetine, and caffeine faster than non-smokers. When a patient stops smoking (planned quit, hospitalization, respiratory illness), 1A2 activity drops toward non-smoker levels over a few weeks, and clozapine or olanzapine levels rise. This is a common cause of unexpected sedation or side effects in a patient who has recently stopped smoking, and it is a scenario where re-checking a level a few weeks after cessation matters.
- Where does the reference data come from?
The substrate, inhibitor, and inducer classifications come from the Flockhart Table of Drug Interactions (Indiana University), FDA drug labeling via DailyMed, and the CPIC (Clinical Pharmacogenetics Implementation Consortium) guidelines. Verbatim reference notes are shown on every result. This tool is a look-up over that reference data. It is not a clinical decision engine and does not personalize to patient factors like genotype, age, or organ function.