Is Fiorinal affected by genetics?

Partially — 1 of 3 ingredients has pharmacogenetic evidence.

Relevant genes: CYP1A2

Fiorinal contains 3 active ingredients, and 1 of them has published pharmacogenetic guidelines. The relevant gene is CYP1A2. Your genotype can change how that ingredient behaves in your body, while the other ingredients aren't affected by genetics in any clinically established way. The strongest evidence level on this page is Moderate, based on CPIC or FDA guidelines.

What's in Fiorinal

butalbital no known pharmacogenetics

No strong published pharmacogenetic guideline currently applies to butalbital.

aspirin no known pharmacogenetics

No strong published pharmacogenetic guideline currently applies to aspirin.

caffeine affected by CYP1A2

Affected by CYP1A2 · Gene2Rx · Moderate evidence

Read the full caffeine genetics guide →

Caffeine phenotype recommendations

Published guidance from Gene2Rx on how caffeine should be dosed or substituted based on your CYP1A2 phenotype.

Phenotype	What it means	Recommendation	Evidence
Ultrarapid Metabolizer CYP1A2	You clear caffeine very quickly, so you may need more or more frequent servings to feel its effects.	Gene2Rx Caffeine is cleared very quickly, which may reduce its stimulant effect. You may require larger or more frequent servings to achieve your desired level of stimulation. Monitor your intake to avoid excessive consumption.	Moderate
Rapid Metabolizer CYP1A2	You clear caffeine quickly, so you might drink more coffee to feel its effects.	Gene2Rx You clear caffeine faster than average, which may shorten its duration of action. You may need more frequent servings to maintain the desired effect. Space your servings to prevent withdrawal symptoms.	Moderate
Normal Metabolizer CYP1A2	You clear caffeine at a normal rate; usual intake guidelines apply.	Gene2Rx Follow standard moderate intake guidelines (≤400 mg/day).	—
Intermediate Metabolizer CYP1A2	You clear caffeine more slowly, so effects last longer—avoid drinking coffee late in the day.	Gene2Rx Standard advice on moderate caffeine intake; consider avoiding late-day caffeine to prevent sleep disturbances.	—
Slow Metabolizer CYP1A2	You clear caffeine slowly, so it stays in your system longer—consider drinking less coffee to avoid jitters or poor sleep.	Gene2Rx Recommend reduced intake (e.g. ≤100 mg/day) and longer intervals between doses to avoid adverse effects.	Moderate
Indeterminate CYP1A2	We don’t know how your genetics affect caffeine metabolism.	Gene2Rx Follow general caffeine guidelines and monitor personal tolerance.	—
Not available CYP1A2	We don’t know how your genetics affect caffeine metabolism.	Gene2Rx Follow general caffeine guidelines and monitor personal tolerance.	—

Source: Gene2Rx

The gene behind the guidance

CYP1A2 Cytochrome P450 1A2

CYP1A2 is the liver enzyme that clears caffeine, clozapine, and a handful of other drugs. Its activity is shaped by both genetics and lifestyle (smoking speeds it up, certain foods slow it down), but the underlying gene still sets your baseline. About 40 percent of people carry a variant that classifies them as rapid metabolizers; the rest process caffeine at an average or slower rate.

Rapid metabolizers clear caffeine quickly and may feel less effect from a given dose. Slower metabolizers feel caffeine longer and at lower doses.

See all drugs affected by CYP1A2 →

Related medications

Find out how your genetics affect Fiorinal

This page describes the general pharmacogenetics. A Gene2Rx report analyzes your own DNA to tell you which metabolizer group you fall into, across every medication.

Get your report Look up another medication

Informational only — not medical advice. Pharmacogenetic guidance describes population-level patterns; your individual response depends on many factors. Never start, stop, or change a medication without talking to your prescribing clinician.