Modafinil is a wakefulness-promoting compound studied extensively in research on shift-work sleep disorder, narcolepsy, and cognitive endurance. It is also the most-searched nootropic compound in the UK in 2026 — but for important regulatory reasons explained below, what most UK researchers actually want is Adrafinil, modafinil’s research-grade legal cousin.

What is Modafinil?

Modafinil is a eugeroic — a class of wakefulness-promoting agents — first developed in France in the 1970s and approved in many countries for narcolepsy, shift-work sleep disorder, and excessive daytime sleepiness associated with obstructive sleep apnoea. Its mechanism involves selective dopamine reuptake inhibition with downstream effects on histamine, orexin, norepinephrine and serotonin systems. Half-life is approximately 12–15 hours.

UK regulatory status — important

In the United Kingdom, Modafinil is a Prescription-Only Medicine (POM) under the Human Medicines Regulations 2012. It cannot lawfully be supplied for self-administration without a valid prescription from a UK-registered prescriber. For this reason, Stackcalc does not provide a Modafinil dosage calculator — there is no legitimate self-administered research use case for the compound in the UK without a prescription.

If you have a UK prescription for Modafinil, follow the dosing your prescriber has set out for you. This page is informational only.

For research, use Adrafinil instead

Researchers and biohackers looking for the cognitive-endurance and wakefulness profile of Modafinil should reach for Adrafinil instead. Here’s why Adrafinil is the right choice for research-grade work in the UK:

• Same downstream activity. Adrafinil is a prodrug for modafinil — once metabolised in the liver, the active compound circulating in the body is modafinil itself.
• Unscheduled in the UK. Adrafinil has never been licensed as a medicine in any major jurisdiction, which means it sits outside the prescription-only regulatory framework that covers modafinil. It is lawfully available as a research-grade compound in the UK.
• Available research-grade. Reputable UK research-peptide and nootropic suppliers stock Adrafinil in capsule and powder form for laboratory and educational use.
• Works on a delay. Adrafinil’s onset is slower than direct modafinil (90–120 minutes typical, vs 60 minutes for modafinil itself) because of the metabolic conversion step. Researchers should account for this in any timing-sensitive protocol.

Open the Adrafinil dosage calculator

Stackcalc has a dedicated Adrafinil page with the dosage calculator, oral-administration timing notes, half-life information, and storage guidance.

Where to source research-grade Adrafinil

Adrafinil is supplied by our trusted UK research-compound partner. The Adrafinil compound page above includes the "Where to source" section linking through to the supplier with our partner discount applied.

Recommended Adrafinil dose for research

You asked for a number rather than a calculator — here’s the consensus across the research and self-experimentation literature. Not medical advice; not for human consumption. This is the dose range most commonly reported in biohacker and research-grade nootropic discussions for Adrafinil.

• Starter dose: 300 mg — one capsule, morning. Roughly 100–120 mg modafinil-equivalent after liver conversion.
• Standard research dose: 600 mg — two capsules, morning only. Roughly 200–240 mg modafinil-equivalent. The most commonly reported dose in self-experimentation reports.
• Upper bound: 1200 mg per day — highest dose with any meaningful safety record in the literature. Above this is uncharted.

Timing

Take Adrafinil only in the morning. Once converted to modafinil it has a half-life of 12–15 hours — dosing later than midday will disrupt sleep. The Adrafinil-to-modafinil conversion takes 90–120 minutes, so onset is slower than direct modafinil. Plan for a delayed effect.

Cycling

The conventional protocol is 5 days on, 2 days off, or cycled around weeks of high cognitive demand only. Continuous daily use is not recommended — Adrafinil places a meaningful conversion load on liver enzymes (ALT and AST elevation has been reported in long-term users), and tolerance to the wakefulness effect develops within 1–3 weeks of continuous dosing.

Quick reference

• First time: 300 mg, morning
• Standard: 600 mg, morning
• Frequency: 5 on / 2 off, max 4 weeks continuous, then break
• Onset: 90–120 minutes
• Duration of effect: 10–14 hours

Quick FAQ

Is Adrafinil legal in the UK?

Adrafinil is not licensed as a medicine in the UK and is not a controlled substance under the Misuse of Drugs Act. Reputable UK research-compound suppliers stock it lawfully for research and educational purposes. It is not for human consumption.

Why doesn’t Stackcalc have a Modafinil calculator?

Because Modafinil is prescription-only in the UK, there is no legitimate self-administered research use case for it without a prescription. We focus on compounds that UK researchers can actually source and study lawfully — which means Adrafinil, not Modafinil.

How does Adrafinil compare to Modafinil for cognitive-endurance research?

Because Adrafinil metabolises into Modafinil, the downstream pharmacology is essentially identical. The differences are practical: slower onset (90–120 min vs 60 min), slightly higher dose required to achieve the same circulating modafinil level (typical Adrafinil oral dose 300–600 mg corresponds to roughly 100–200 mg modafinil equivalent), and a small additional liver-enzyme load from the conversion step. For most research protocols this is a reasonable trade-off given the regulatory accessibility.

Compliance reminder: All content on Stackcalc is for research and educational purposes only. We do not sell, supply or recommend compounds, and nothing on this site constitutes medical advice. Modafinil is a UK prescription-only medicine and Adrafinil is a research-grade compound not licensed for human consumption.