The 71% Problem: What's Actually in Your Melatonin Supplement

Published January 2025 · 7 min read

A landmark study found that 71% of melatonin supplements don't contain what their labels claim. Some had nearly 5x the labeled dose. Others contained unlisted serotonin. Here's what the research shows and why it matters for your sleep.

When you buy a supplement, you expect it to contain what the label says. With melatonin, that expectation is often wrong.

In 2017, researchers at the University of Guelph published a study in the Journal of Clinical Sleep Medicine that should have changed how we think about melatonin supplements. They purchased 31 melatonin products from stores and online retailers, then sent them to an independent lab for analysis.

The results were alarming.

What the Study Found

More than two-thirds of the products tested contained significantly more or less melatonin than their labels claimed. The range was staggering—from 83% less than labeled to 478% more.

Think about that. If you're taking a 3mg melatonin supplement, you might actually be getting anywhere from 0.5mg to 14mg. You have no way to know which.

Why Does This Happen?

Unlike pharmaceutical drugs, dietary supplements in the US aren't required to prove their contents match their labels before going to market. The FDA regulates supplements under DSHEA (Dietary Supplement Health and Education Act), which puts the burden of proof on the FDA to show a product is unsafe—not on manufacturers to prove it's accurately labeled.

This means supplement companies can:

Use varying quality raw materials. Melatonin synthesis isn't perfectly consistent. Different batches of raw material have different potencies.

Skip batch testing. Testing every batch costs money. Many companies test infrequently or not at all.

Have inconsistent manufacturing. Mixing a small amount of active ingredient evenly into a large batch of pills is harder than it sounds. Uneven distribution means some pills have more, some have less.

The serotonin contamination is particularly concerning. Serotonin is a neurotransmitter precursor that's regulated as a drug, not a supplement. Its presence suggests either contaminated raw materials or poor manufacturing controls.

What This Means for You

If you're taking melatonin and experiencing inconsistent results—working great some nights, not at all others—this might explain it. You're essentially taking a random dose each night.

For people taking melatonin for children (a common use), the implications are more serious. A child given a "1mg" gummy might actually receive nearly 5mg—a dose that could affect hormonal development.

Which Products Were Tested?

The study didn't name specific brands—a common practice in academic research to avoid legal issues. However, they did report that:

Gummies and chewables were worst. These formats showed the highest variability, likely because it's harder to distribute active ingredients evenly in a gummy matrix.

Capsules were somewhat better. But still, the majority didn't match their labels.

Brand recognition didn't help. Popular, well-known brands weren't more accurate than lesser-known ones.

How to Find Reliable Products

If you're going to use melatonin (we'd suggest considering alternatives, but that's your choice), here's how to improve your odds:

Look for Third-Party Testing

Products certified by NSF International, USP, or ConsumerLab have been independently verified. This doesn't guarantee perfection, but it's better than nothing.

Check for Published COAs

Some brands publish Certificates of Analysis for their batches. If a company won't share COAs, that's a red flag.

Avoid Gummies

The research suggests capsules and tablets are more consistent than chewable formats.

Start Low

Given the variability, starting with a low labeled dose (0.5-1mg) gives you a buffer if the actual content is higher than claimed.

A Better Approach: Alternatives That Require Verification

One argument for non-melatonin sleep supplements is that quality can be verified more easily. For example:

With magnesium, the mineral content can be verified through standard assays. With amino acids like L-theanine, purity testing is straightforward.

Melatonin's problem isn't just that it's a hormone with tolerance issues—it's that you can't reliably know what you're getting.

The Bigger Picture

The melatonin mislabeling study highlights a broader problem with the supplement industry: you often don't know what you're buying. Melatonin is particularly problematic because:

It's a hormone. Dosing matters more than with many supplements. Too much can suppress natural production; too little won't work.

It's cheap to produce. The market is flooded with low-cost products competing on price rather than quality.

Most users don't know better. Melatonin has a "natural" reputation that makes people assume it's safe and well-regulated.

If you're going to use any sleep supplement, do your research on the specific brand and product. Look for third-party verification. And consider whether melatonin—with all its quality control issues—is really the best option when alternatives exist.