Modafinil interactions

This page is a reference summary of published evidence and regulatory documents. It is not a substitute for individual medical advice, and it is not a recommendation to take or avoid any medicine.

Medically reviewed by Dr. Sofia Lindqvist, · Last reviewed 26 March 2026

Modafinil’s interactions come mainly from two liver enzyme effects: it induces CYP3A4, which lowers blood levels of drugs cleared by that pathway, and it inhibits CYP2C19, which raises blood levels of drugs cleared by that pathway. The clinically significant consequence for most people is reduced hormonal contraceptive reliability; several other interactions matter for specific medications.

The mechanism in plain language

CYP3A4 and CYP2C19 are liver enzymes that break down a large share of prescription drugs. Induction means modafinil increases the amount of the enzyme available, so drugs processed by it are cleared from the body faster and reach lower peak levels than expected. Inhibition means modafinil blocks the enzyme, so drugs processed by it are cleared more slowly and can accumulate.

These effects build up over days as enzyme levels adjust and fade over a similar timescale after modafinil is stopped, rather than switching on and off with a single dose.

Drugs modafinil decreases

Drug	Effect	Approximate magnitude
Hormonal contraceptives (ethinyl estradiol)	Reduced contraceptive reliability	~18% increase in clearance
Cyclosporine	Reduced immunosuppressant levels	~50% reduction reported
Midazolam	Reduced sedative effect	Clinically relevant with oral dosing
Triazolam	Reduced sedative effect	Clinically relevant with oral dosing

Effects are via CYP3A4 induction.

Drugs modafinil increases

Drug	Effect	Notes
Warfarin	Increased anticoagulant effect	Monitor INR when starting or stopping modafinil
Phenytoin	Increased phenytoin levels	Narrow therapeutic index — monitor levels
Diazepam	Prolonged sedative effect	Via CYP2C19 inhibition
Propranolol	Increased beta-blocker exposure	Via CYP2C19 inhibition
Omeprazole	Increased proton-pump inhibitor levels	Via CYP2C19 inhibition
Some SSRIs and TCAs	Increased drug levels in CYP2C19 poor metabolisers	Effect size varies by genotype

Drugs that affect modafinil levels

Strong CYP3A4 inducers, such as rifampicin and carbamazepine, can lower modafinil exposure and reduce its effect. Strong CYP3A4 inhibitors, such as ketoconazole, can raise modafinil exposure. Neither interaction is as well characterised as modafinil’s effect on other drugs, since modafinil’s own clearance is only partly CYP3A4-dependent.

Alcohol and other stimulants

Modafinil has no established pharmacokinetic interaction with alcohol. The practical concern is that modafinil’s alertness effect can mask alcohol-related impairment in judgement, reaction time and coordination without reducing the impairment itself.

Combining modafinil with other stimulants (amphetamines, methylphenidate, high-dose caffeine) has not been systematically studied for safety and is generally avoided in clinical practice because cardiovascular effects — heart rate and blood pressure — are additive in principle even without direct trial data.

A review checklist

Before starting modafinil

Confirm current hormonal contraceptive use and discuss a non-hormonal or additional method for the duration of treatment and two months after stopping. List all other medications and check whether any are CYP3A4 or CYP2C19 substrates, particularly warfarin, phenytoin, and immunosuppressants. Flag any strong CYP3A4 inducers or inhibitors already in use.

Frequently asked questions

What does modafinil do to other drugs in the body?

It induces the liver enzyme CYP3A4, which speeds up clearance of drugs metabolised by that pathway, and inhibits CYP2C19, which slows clearance of drugs metabolised by that pathway.

Does modafinil make birth control less effective?

Yes. CYP3A4 induction increases clearance of ethinyl estradiol by around 18%, and a non-hormonal or additional method is advised during use and for two months after stopping.

Is modafinil safe to combine with alcohol?

There is no direct pharmacokinetic interaction, but alcohol impairs judgement and coordination in ways modafinil’s alertness effect can mask, which is a practical rather than a metabolic concern.

Does grapefruit juice affect modafinil?

Grapefruit juice inhibits intestinal CYP3A4, but modafinil’s own metabolism is primarily via amide hydrolysis and CYP3A4 to a lesser extent, so the clinical effect is modest compared with drugs that rely heavily on that pathway.

What should a prescriber check before starting modafinil?

A full medication list, focusing on hormonal contraceptives, other CYP3A4/CYP2C19 substrates such as warfarin or phenytoin, and any strong CYP3A4 inhibitors or inducers the patient is already taking.