Melatonin Isn’t Just for Sleep: What 38 Women Found Out

Melatonin has one job in most medicine cabinets: knock you out. But what if the same pill you take at 10 p.m. quietly made your morning workouts pay off more? A team at the University of Sfax tested exactly that — and the answer might change how you see the most boring supplement on your nightstand.

The Setup: 38 Women, 12 Weeks, One Tiny Pill

Every woman was randomly placed into one of three groups. Group one did concurrent training — a mix of cardio and strength work, three sessions a week — and took 3 mg of melatonin every night. Group two did the exact same training but got a placebo pill. Group three kept living normally: no training, no pill.

Before and after the 12 weeks, the researchers drew blood and measured cholesterol, blood sugar, liver enzymes, creatine kinase (a marker tied to muscle stress), body composition, and waist and hip size. The study was published on October 10, 2026, in the journal Experimental Gerontology.

The design is the clever part. Because one training group got melatonin and the other got a placebo, any extra benefit in the melatonin group can be linked to the supplement — not just the exercise.

Training Alone Was Good. Melatonin Made It Better.

First, the unsurprising part: exercise worked. Both training groups lost fat, trimmed their waists and hips, and gained muscle compared with the group that did not train.

Now the surprising part. The women who took melatonin on top of training got extras the training-only group did not:

In plain English: workouts reshaped bodies; melatonin added a bonus round for blood markers — cholesterol, blood sugar, liver numbers. Only the melatonin group also saw drops in white blood cells and urea, plus higher mineral levels.

Their conclusion was measured: melatonin plus training was “more effective than training alone” for LDL cholesterol and triglycerides. A careful, specific claim — not a victory lap.

The Fine Print: Read This Before You Get Excited

One small trial: thirteen women per group, twelve weeks, and every participant was a postmenopausal woman. Small studies sometimes look impressive until a bigger one shrinks the effect — and these results may not apply to younger adults or men.

Melatonin’s licensed job description is sleep, not fitness. This single study does not rewrite that — it raises a question; it does not settle one.

The Canadian Angle: What 3 mg Means on a Canadian Shelf

The 3 mg dose in the trial sits comfortably inside Health Canada’s licensed range: 0.1 mg to 10 mg a day for adults 18 and older, taken 30 to 60 minutes before bedtime. So the women in this study took a dose you could find in any Canadian drugstore — nothing exotic.

Canada also drew a firm line this year on who melatonin is for. On June 2, 2026, Health Canada changed the Prescription Drug List so melatonin sold for sleep-related use in anyone under 18 is now prescription-only. Every licensed melatonin natural health product in Canada is indicated for adults only.

And its licensed uses are still sleep-related — “workout booster” is not on the label, and one small trial does not put it there.

What is melatonin and how is it supposed to work?

Melatonin is a hormone that helps regulate sleep, as Health Canada puts it. Your body makes it when it gets dark — part of how your brain knows it is bedtime. The melatonin in supplements is synthetic, made in a lab, and meant to nudge that same sleep-wake signal.

Licensed uses in Canada are sleep-only: falling asleep faster, more total sleep on disrupted schedules (think shift work), less jet lag, and resetting your body clock. Anything beyond sleep — like the workout-linked effects in this trial — is outside what the products are licensed for.

What are the side effects of melatonin?

Melatonin has a gentle reputation, and for most adults it holds — but “natural” is not “risk-free.” From Health Canada’s monograph:

Stop using it and talk to a professional if you get a headache, confusion, or nausea. Because it causes drowsiness, avoid alcohol and other products that make you sleepy, and do not drive or operate machinery for about five hours after taking it.

Check with a practitioner first if you take seizure, blood pressure, immune-suppressing, mental-state, sedation, steroid, or blood-thinner medications — or if you have heart, immune, liver, or kidney disease, a seizure disorder, asthma, or diabetes. Do not use it if you are pregnant or breastfeeding, and see a practitioner if sleeplessness lasts more than four weeks.

How much melatonin should you take?

The trial used 3 mg a night — mid-range of Health Canada’s licensed 0.1 to 10 mg a day for adults. The researchers never tested 10 mg; 3 mg is what produced the results.

The licensed range starts very low, and bigger is not automatically better. For sleep, the monograph says to take it as needed, 30 to 60 minutes before bed — a pharmacist can help you pick a starting point.

What should you look for on the label?

Start with the NPN — the eight-digit Natural Product Number proving Health Canada licensed the product.

Check that the label says the product is for adults. As of 2026, no melatonin natural health product is authorized for children or teens in Canada, and pediatric sleep-related use now requires a prescription.

Be skeptical of big promises. Health Canada forbids vague “supports good health” claims on melatonin, and licensed claims are sleep-specific. A label that talks about curing disease is a red flag. Look for clear directions — dose per capsule, “30 to 60 minutes before bedtime” — plus the standard drowsiness and driving warnings.

This article reports on recent health research and is for general information only — it isn’t medical advice and doesn’t replace your doctor, pharmacist, or another qualified professional. Study findings describe what researchers observed, not a promise of results, and nothing here claims any supplement can diagnose, treat, cure, or prevent a disease. These statements have not been evaluated by Health Canada. Check with a healthcare professional before starting any new supplement, especially if you’re pregnant, nursing, taking medication, or managing a health condition.