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Press / to focus. Search a name, or tap a starter below — add two items to see mapped pair findings.

Educational interaction checker

Explore possible medicine and substance interactions.

Add two or more medicines, supplements, foods, or other substances to see possible concerns in everyday language, with clinical details and sources for review. This is a learning aid for clinicians and supervised education—not personal medical advice. It can miss interactions; no result does not mean a combination is safe.

1SearchUse a generic name, brand, or common name.
2Add anotherChoose a second item to check the pair.
3ReviewStart with the everyday-language summary; open sources for context.

Try an example

Examples load into the checker so you can see how its summaries and source links work.

Desk

Formulary: 1835
On desk: 0/5
Findings: 0
License: Free

Ceiling — · free · founding $79 lifetime unlocks host factors / atlas / export

How ketamine goes inKetamine route

Free on this desk. Ketamine by mouth with grapefruit is the teaching demo for the gut first pass. The other host factors come with founding.

IV / IM mostly skips gut first-pass; hepatic CYP2B6 still clears it.

About this personHost factors

How this works

The same drugs can act differently in different people. Pick only what you already know about this person (a metabolizer status from their chart, smoking, drinking, age, kidneys, pregnancy) and the desk re-reads every pair with that in mind.

A slow built-in enzyme acts a lot like a drug that blocks that enzyme. Smoking speeds up the 1A2 enzyme. Heavy long-term drinking speeds up the 2E1 enzyme. Older age, weaker kidneys, and pregnancy open extra teaching cards (Beers list, kidney, and pregnancy notes).

Everything is set to typical. A typical person, or a quiet result, is not a green light: real people vary, and genetics are rarely known at the desk. Product labeling and the clinician govern.

Built-in enzyme speedMetabolizer phenotype · CPIC paraphrase

Pick a metabolizer status you already know. This is a teaching summary of CPIC guidance, not a genetic test result.

CYP2D6
DXM, MDMA, codeine, atomoxetine
CYP2C19
Clobazam, diazepam, citalopram
CYP2C9
Warfarin, phenytoin, edible THC
CYP2B6
Ketamine, bupropion, methadone

SmokingTobacco smoke · CYP1A2 inducer

Unlocking this teaches how smoke speeds CYP1A2 clearance — the classic clozapine / olanzapine lesson.

DrinkingAlcohol pattern · CYP2E1

Unlocking this teaches acute sedation stacking and chronic CYP2E1 induction — two different alcohol stories.

How cannabis is takenCannabis route

Smoked THC mostly skips the edible first-pass that makes 11-OH-THC.

AgeAge band · Beers list

KidneysRenal function · GFR

Pregnancy or breastfeedingPregnancy / lactation

Teaching only. The enzyme speed rows are a plain summary of CPIC guidance for a status you already know. They are not a genetic test result, not a gene report reading, and not a reason to change any medicine.

Host factors need founding

Teaching cards for metabolizer status (phenotype), smoking, alcohol pattern, cannabis route, age, kidney function, and pregnancy sit behind founding. The ketamine route stays free for the oral teaching demo.

Free desk: up to five drugs, no card needed. Founding is $79 once.

Pay, get your key, Redeem · Pay $79 once, Get your key, Redeem on this desk

Founding unlocks host factors, enzyme atlas, metabolite maps, full report, and JSON/CSV export — $79 once. Educational model; not FDA-cleared.

Pay, get your key, Redeem · Venmo @kaleblovingier · Cash App $kaleblovingier7 · PayPal FirstPassInteractions@gmail.com · card when Stripe is live

How it scores

PK. Strong inhibitors of sensitive or narrow-index substrates grade contraindicated; induction of clearance is loss of efficacy.
Curve. Grey is this route, normal metabolizer, no blockers. Teal is this desk. q8h / q12h / q24h show how doses stack (build-up / Rac). Overlay IV vs oral on first-pass victims. Not a plasma level. Five-drug exposure (AUCR) stays free.
2D6. Blockade of codeine or tamoxifen is lost activation; of DXM or MDMA it is stacked parent plus serotonin.
Phenotype. Flip CYP2D6 / 2C19 / 2C9 / 2B6 to poor or ultrarapid — a poor metabolizer scores like a strong inhibitor of that enzyme. Poor 2C9 metabolizers make warfarin and edible THC hotter.
Host. Daily smoke induces CYP1A2. Chronic alcohol induces CYP2E1 (NAPQI from acetaminophen). Oral ketamine and edible THC are first-pass victims; IV and smoked mostly skip it.
Food. Grapefruit knocks out intestinal 3A4. Tyramine plus an MAOI is a pressor crisis. Piperine and pomegranate are quieter 3A4 hits. Licorice drops potassium. Fat meals raise oral THC/CBD. Salt and urine pH move lithium and amphetamine.
Supplement. Red yeast rice is lovastatin. Berberine is a 3A4/P-gp bully plus a glucose drop. SAM-e and 5-HTP are serotonergic. Vitamin K dumps INR; nattokinase and fish oil bleed. Calcium/iron chelate Cipro and Synthroid. Charcoal and psyllium bind the morning dose. Niacin plus a statin is muscle. Search supplement / vitamin / otc.
Street. Cocaine plus ethanol is cocaethylene. Stimulant plus opioid is a speedball — the stimulant masks apnea. Dirty 30s are pressed fentanyl ± xylazine, not oxycodone; naloxone will not reverse the α2. Percocet is oxy + APAP. HR tab: never use alone, recovery position, test-strip limits, GHB steep curve, MDMA heat/water, TripSit combo ratings, live PsychonautWiki intros with milligrams stripped. A wiki is not a label — independently review. Not a cooking guide.
MAT. Put methadone or a film on the desk, then tap today's extra on the window tray. Buprenorphine on a fentanyl load is precipitated withdrawal, not stacked milligrams. Methadone lives on 3A4/2B6 — inducers look like a stolen dose; azoles, Vistaril, and Zofran are the QT traps. Paxlovid dumps methadone and raises fentanyl; cobicistat (Tybost) is the opposite arrow on methadone. Gabapentinoids are not free extras on an opioid airway. Lofexidine is α2 — naloxone will not reverse it. Epclusa next to methadone should stay quiet; rifampin should not. The window briefing is watch / counsel / hold — copy the huddle onto a note. Not a protocol.
CYP clock. Strong / moderate / weak are FDA fold-change grades (Huang 2007 / 2020 guidance), not vibes. Mechanism-based inhibitors (clarithromycin, grapefruit, ritonavir, paroxetine, fluoxetine) destroy the enzyme — stopping yesterday does not restore it. Inducers take a week to land and two weeks to leave; the stop is rebound toxicity. Open the CYP tab. Plan the stop on the start day. Not a milligram.
Clinic. Allopurinol × azathioprine is xanthine oxidase, not CYP — pancytopenia. Nitrates × PDE5 are labeled hypotension. Omeprazole blunts clopidogrel activation (2C19 prodrug); pantoprazole is the quieter switch. Oral budesonide and swallowed fluticasone are gut 3A4 first-pass victims — azoles and ritonavir make a 'local' steroid systemic. Terbinafine is a strong 2D6 inhibitor, not an azole. Ozempic next to a sulfonylurea is hypoglycemia; next to metformin it should stay quieter. Search clinic / primary / ozempic / imuran.
Host clinic. Flip geriatric for Beers 2023. CKD scores renally cleared NTI drugs and NSAIDs. Pregnant flags ACEI/ARB, warfarin, valproate, MTX, mycophenolate. Teaching notes, not a label. Search beers / pregnant.
Sources. DrugBank is identity and targets — open the accession. PharmGKB / CPIC is the gene table; flip a metabolizer on this desk and the matching row highlights. Stahl is a receptor sketch (spectrum, occupancy, side effects from those receptors) in original language, not a quotation of the book. PubMed is a curated PMID shelf plus a live NCBI search for the pair on the desk. Search pgx / stahl / drugbank / pubmed.

About this desk

Built for learning and clinical review — not a personal treatment guide. FirstPass 1.75.0 is an educational clinical decision-support aid for clinicians and supervised learning. This software has not been cleared or approved by the U.S. Food and Drug Administration. Display of FDA-label text does not make FirstPass an FDA-cleared device. It can miss risks; an empty result is not proof that a combination is safe. It does not identify product contents, diagnose, or tell anyone what to start, stop, or change. For care decisions, consult a qualified clinician and current FDA-approved labeling. Street-supply entries are teaching examples, not product identification.

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