Modafinil: what it is, how it works and who it’s for

Modafinil is a prescription-only medicine that helps adults with narcolepsy stay awake during the day. In the UK it is licensed only for excessive sleepiness caused by narcolepsy, with or without cataplexy. It is usually started by a sleep specialist, and it needs regular checks on your heart, blood pressure and mental health.

In this guide:

• What modafinil is
• What modafinil is used for (and what it is not for)
• How modafinil works
• How modafinil is taken
• Where it fits in narcolepsy treatment
• Side effects and safety checks
• Who should not take it
• Pregnancy and contraception
• Interactions with other medicines
• Legal status, dependence and driving

What is modafinil?

Modafinil is a medicine that promotes wakefulness. It was developed to reduce the overwhelming daytime sleepiness that some sleep disorders cause.

The official prescribing information (SmPC) for modafinil 100 mg tablets lists it as a prescription-only medicine. In the UK it comes as 100 mg and 200 mg tablets, and you may also see the brand name Provigil.

The NHS page on treating narcolepsy lists modafinil alongside pitolisant and solriamfetol as daytime “stimulant” medicines. It works differently from older stimulants such as amphetamines, which we explain below.

If you are still finding out what narcolepsy is and how it is diagnosed, start with our guide to narcolepsy and excessive sleepiness.

What is modafinil used for?

In the UK, modafinil has one licensed use. It treats excessive sleepiness associated with narcolepsy, with or without cataplexy, in adults aged 18 and over.

Narcolepsy is a long-term condition in which the brain struggles to control when you sleep and when you are awake. People with it can feel very sleepy all day and may fall asleep suddenly. Cataplexy is a sudden, brief loss of muscle control, often triggered by strong emotions such as laughter.

The SmPC says modafinil should only be used after a full assessment of your sleepiness, with narcolepsy diagnosed using recognised clinical criteria. In practice, this means a specialist sleep assessment comes first.

Modafinil helps with daytime sleepiness. It does not cure narcolepsy, and it is not mainly used to treat cataplexy.

Why the licence was narrowed in 2010

Modafinil used to have a wider licence. In July 2010 the European Medicines Agency recommended restricting modafinil to sleepiness caused by narcolepsy alone.

Its experts removed three uses: obstructive sleep apnoea, chronic shift work sleep disorder and idiopathic hypersomnia. For those conditions, they found the risks of skin reactions and mental health problems outweighed the evidence of real benefit.

The UK regulator, the MHRA, followed this. Its Drug Safety Update on the restriction told prescribers that modafinil is no longer indicated for shift-work sleep disorder or obstructive sleep apnoea.

What modafinil is not licensed for

Modafinil is not licensed in the UK for:

• Improving concentration, memory or exam performance in healthy people
• Tiredness from shift work or long hours
• Sleepiness caused by obstructive sleep apnoea
• ADHD, depression or fatigue from other conditions
• Children and teenagers under 18

A specialist may sometimes consider a medicine outside its licence, but that is a clinical decision made case by case. It is not something to try yourself.

The MHRA has warned students directly. Its 2016 warning to freshers stressed that modafinil is licensed for specific medical conditions, not as a boost during exams.

How does modafinil work?

Nobody knows exactly how modafinil keeps you awake. The SmPC says its precise mechanism is still unknown.

What is known is that modafinil acts on dopamine, a chemical messenger involved in alertness and motivation. It binds to the dopamine transporter, which normally clears dopamine away after it has been released. By blocking that clearance, it leaves more dopamine active in the brain.

It also has weaker effects on the transporter for noradrenaline, another alertness chemical. According to the SmPC, it acts mainly on brain areas involved in arousal and vigilance, unlike classic stimulants that act more widely.

How long does modafinil stay in the body?

After repeated doses, the SmPC gives an effective half-life of about 15 hours. That is the time it takes for the level in your blood to fall by half.

This long half-life is one reason modafinil is taken early in the day. Taken late, it is more likely to disturb your night-time sleep.

How is modafinil taken?

Always take modafinil exactly as your prescriber tells you. Your dose is set and adjusted by your specialist, based on how you respond.

The SmPC and patient information leaflet describe the usual approach for adults:

• The usual starting dose is 200 mg a day.
• It can be taken once in the morning, or split into a morning dose and a midday dose.
• If 200 mg is not enough, a doctor may increase it to 400 mg a day, in one or two doses.
• For people over 65, treatment usually starts at 100 mg a day.
• In severe liver problems, the SmPC advises halving the dose.

Swallow the tablets whole with water. If you miss a dose, the leaflet says to take the next one at the usual time. Do not take a double dose to make up for it.

If you think you have taken too much, contact a doctor or go to your nearest A&E straight away. Take the leaflet and any remaining tablets with you.

Regular reviews

Modafinil is often a long-term treatment, so your specialist will review it regularly. The SmPC notes that long-term effectiveness has only been studied for up to 9 weeks, so periodic reassessment is advised.

Modafinil does not replace sleep. The SmPC advises keeping good sleep habits, including reviewing how much caffeine you have.

Where does modafinil fit in narcolepsy treatment?

Medicine is only one part of managing narcolepsy. The NHS recommends lifestyle changes alongside it, including:

• Short, planned naps spread through the day
• A regular bedtime and wake-up time
• Avoiding caffeine, alcohol and smoking before bed
• Avoiding heavy meals and exercise close to bedtime
• Checking with a pharmacist before using cold or allergy remedies that can cause drowsiness

The NHS describes several groups of medicines that a specialist may use:

Type of medicine	Examples named by the NHS	Main purpose
Daytime “stimulants”	Modafinil, pitolisant, solriamfetol	Reduce daytime sleepiness
Sodium oxybate	Liquid taken in two night-time doses	Improve night-time sleep and daytime symptoms
Antidepressants	Some SSRIs, an SNRI and tricyclics	Help with cataplexy, hallucinations and sleep paralysis

Which medicine suits you depends on your symptoms, other health conditions and whether you could become pregnant. These choices are made with your sleep specialist. Our narcolepsy guide covers the condition and its non-medicine treatments in more detail.

Side effects and safety checks

Like all medicines, modafinil can cause side effects, although not everyone gets them. The most common is headache. The SmPC reports it in about 21% of people, usually mild to moderate.

The patient leaflet lists these common side effects, which may affect up to 1 in 10 people:

Area	Common side effects
Nervous system and mood	Dizziness, sleepiness or trouble sleeping, irritability, pins and needles
Heart and circulation	Feeling your heart beat fast, chest pain, flushing
Stomach and appetite	Loss of appetite, feeling sick, stomach pain, indigestion, diarrhoea, constipation, dry mouth
Other	Weakness, blurred vision, changes in liver blood tests

For every listed side effect, how often it happens and what to do, read our guide to modafinil side effects.

Serious side effects to act on straight away

The leaflet says to stop taking modafinil and see a doctor straight away if you have:

• Sudden wheezing, difficulty breathing, or swelling of the face, mouth or throat
• A skin rash or itching, especially over your whole body
• Blistering, peeling skin, ulcers in the mouth, eyes or genitals, or a fever with a rash
• Changes in your mental health, such as mood swings, aggression, anxiety, depression, agitation or thoughts of suicide

Serious skin reactions are rare, but they matter. The SmPC says they have usually appeared within 1 to 5 weeks of starting treatment. If your doctor stops modafinil for a rash or a mental health reaction, it should not be restarted.

Checks before and during treatment

Because modafinil can affect the heart, the SmPC advises an ECG (heart tracing) before you start. Your blood pressure and heart rate should then be checked regularly. Our guide to modafinil, your heart and blood pressure explains these checks and what is known about long-term use.

Your prescriber should also ask about your mood and mental health at each dose change and at regular reviews. Tell them about any history of depression, psychosis, mania, or alcohol or drug problems.

Who should not take modafinil?

The SmPC says modafinil must not be used if you:

• Are allergic to modafinil or any of the tablet’s ingredients
• Have moderate to severe high blood pressure that is not controlled
• Have an irregular heartbeat (cardiac arrhythmia)

It is not recommended for some other heart problems, including left ventricular hypertrophy. It is also not recommended for anyone under 18.

Extra care is needed if you have had serious anxiety, bipolar disorder, depression or psychosis. The tablets also contain lactose, which matters if you have a rare sugar intolerance.

Modafinil, pregnancy and contraception

Modafinil should not be used during pregnancy. In November 2020 the MHRA warned of an increased risk of birth defects, including heart defects, hypospadias and cleft lip or palate.

The warning drew on interim data from a US pregnancy registry. It found major birth defects in about 14.75% of babies exposed to modafinil, compared with about 3% in the general population. This was based on 61 live births, and the registry had not yet reached its target size.

If you could become pregnant, the MHRA’s public advice is:

• Use effective contraception while you take modafinil.
• Keep using it for 2 months after you stop.
• Remember that modafinil can make hormonal contraception, including the pill, less effective. Ask your doctor about other or additional methods.
• Talk to your doctor early if you are planning a pregnancy.
• Read our guide to modafinil, pregnancy and contraception for which methods still work and the two-month rule.

The SmPC also says modafinil should not be used while breastfeeding. Do not stop a prescribed medicine suddenly without advice; speak to your specialist first.

Does modafinil interact with other medicines?

Yes. Modafinil changes how the liver handles several other medicines, so always tell your doctor and pharmacist everything you take. The SmPC highlights:

• Hormonal contraceptives: modafinil can make them less effective, as explained above.
• Ciclosporin: modafinil may lower its levels.
• Warfarin: blood clotting tests should be checked more closely when modafinil is started or the dose changes.
• Phenytoin: levels may rise, so monitoring for side effects is advised.
• Some other medicines, such as diazepam, propranolol, omeprazole and certain antidepressants, may need dose changes.
• Carbamazepine and phenobarbital may lower modafinil levels.

This list is not complete. Check with a pharmacist before starting any new medicine, including herbal and over-the-counter products.

For alcohol, caffeine and a medicine-by-medicine table, read our guide to modafinil interactions with alcohol, caffeine and other medicines.

Legal status, dependence and driving

Is modafinil legal in the UK?

Modafinil is legal when it is prescribed for you. Its legal category in the UK is prescription-only medicine (POM), which is listed in its SmPC.

That differs from medicines such as zopiclone, which is also a controlled drug under the Misuse of Drugs Act. Modafinil’s product information lists it as POM only. Our guide to whether modafinil is legal in the UK explains the law on supply and the penalties in more detail.

The MHRA has warned that supplying prescription-only medicines to people who have no valid prescription is a criminal offence. It also warns that unregulated websites may supply fake or unlicensed products.

Can modafinil cause dependence?

The SmPC says studies have shown a potential for dependence, and a risk with long-term use cannot be fully ruled out. This is why your prescriber will ask about any past alcohol or drug problems.

Take only the dose you are prescribed. Speak to your specialist before changing or stopping your treatment.

Modafinil and driving

If you have narcolepsy, the GOV.UK guidance on narcolepsy and driving says you must tell the DVLA. Not reporting a medical condition that affects your driving can lead to a fine, and to prosecution if you have an accident because of it.

Modafinil may not bring your alertness fully back to normal. It can also cause blurred vision or dizziness. Do not drive or use machinery if you are affected or still feel very sleepy, and follow your specialist’s advice.

This article is for information only and does not replace advice from your doctor or pharmacist. Read our medical disclaimer.