Modafinil side effects

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 11 August 2026

Most people taking modafinil experience mild, common effects such as headache, nausea, or nervousness. A small number experience serious reactions — including skin reactions and psychiatric effects — that require stopping the drug and seeking care.

Serious reactions: what to watch for

Seek care immediately for any rash

Modafinil carries an FDA label warning for serious skin reactions, including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and DRESS (drug reaction with eosinophilia and systemic symptoms). These reactions are rare but can be fatal, and there is no way to predict who will develop one.

Any new rash — with or without fever, sore throat, mouth sores, blistering, facial swelling, or eye irritation — should be treated as a possible early sign. Stop modafinil and seek medical evaluation immediately; do not wait to see whether the rash worsens. Angioedema and anaphylaxis have also been reported and require emergency care.

Common effects

The following incidence figures come from placebo-controlled trials in the FDA prescribing information for modafinil across its approved indications.

Effect	Modafinil	Placebo
Headache	~34%	~23%
Nausea	~11%	~4%
Nervousness	~7%	~3%
Insomnia	~5%	~1%
Anxiety	~5%	~2%
Dizziness	~5%	~2%

Approximate incidence, pooled across trials in narcolepsy, OSA, and shift work disorder. Figures rounded from the FDA label.

Most common effects are mild to moderate and occur early in treatment. They do not reliably predict who will experience a serious reaction.

Serious dermatologic reactions

SJS, TEN, and DRESS are rare but are the reason modafinil carries a specific dermatologic warning on its label. These reactions typically develop within the first weeks of treatment, though DRESS can appear later, sometimes two to eight weeks after starting. There is no established way to screen for risk in advance; the response is to stop the drug and seek care at the first sign of a rash, not to wait for confirmation.

Psychiatric effects

Beyond common nervousness and anxiety, modafinil has been associated with less frequent but more serious psychiatric effects, including mania, hallucinations, delusions, aggression, and suicidal ideation. These have occurred both in people with and without a prior psychiatric history. New or worsening mood, thinking, or behaviour changes warrant prompt evaluation.

Cardiovascular effects

Modafinil can cause modest increases in blood pressure and heart rate. The label advises caution in patients with a history of left ventricular hypertrophy or mitral valve prolapse who have previously experienced cardiac effects with CNS stimulants, and recommends blood pressure monitoring in patients with pre-existing hypertension.

When to stop

Stop modafinil and seek medical attention for: any new rash, mouth or eye sores, blistering or peeling skin, swelling of the face, lips, tongue or throat, difficulty breathing, chest pain, or new or worsening depression, agitation, or thoughts of self-harm.

For common effects such as mild headache or nausea, many people continue treatment while the effect resolves, but persistent or bothersome symptoms should be discussed with the prescriber. See modafinil dosage for how dose relates to tolerability.

What is not well characterised

Long-term safety data beyond the trial periods used for approval (typically weeks to months) are limited. The incidence and risk factors for serious skin and psychiatric reactions are not precisely quantified beyond “rare,” and there is no validated way to predict individual susceptibility. Interaction-related safety in off-label use, and safety in pregnancy, are addressed separately — see modafinil interactions and modafinil and pregnancy.

Frequently asked questions

What is the most common modafinil side effect?

Headache, reported by approximately 34% of patients in trials versus 23% on placebo. Nausea, nervousness, and insomnia are also common.

Can modafinil cause a serious skin reaction?

Rarely. Modafinil carries a label warning for serious skin reactions including Stevens-Johnson syndrome, toxic epidermal necrolysis, and DRESS (drug reaction with eosinophilia and systemic symptoms). Any new rash should prompt immediate medical attention and discontinuation.

Does modafinil cause anxiety?

Anxiety and nervousness are listed among the common effects in trials. Modafinil can also, less commonly, be associated with more significant psychiatric effects, including mania, hallucinations, and suicidal ideation.

Is modafinil hard on the heart?

Modafinil can cause modest increases in blood pressure and heart rate in some people, and the label warns about use in patients with left ventricular hypertrophy or a history of mitral valve prolapse with prior stimulant-associated cardiac events.

When should I stop taking modafinil and call a doctor?

Stop and seek medical care immediately for any rash, mouth sores, blistering, swelling of the face or throat, chest pain, or new or worsening mood or behaviour changes.