What ingredients should you avoid in sleep supplements?
Last updated: August 2026 · Reviewed by the FactoWiki Editorial Team for clarity and source accuracy
Avoid diphenhydramine and doxylamine (antihistamines sold as natural sleep aids), melatonin above 3 mg unless advised, kava, and any proprietary blend that hides the melatonin dose. Valerian deserves caution rather than avoidance because of rare liver reports.
Key takeaways
- Diphenhydramine is a drug, not a supplement — tolerance builds within days.
- Kava has been linked to severe liver injury and is restricted in several countries.
- A proprietary blend that hides the melatonin dose is the most common problem.
Antihistamines masquerading as sleep aids
Diphenhydramine and doxylamine appear in many products positioned as natural. They are drugs with well-documented next-day impairment, tolerance that develops within days to a week, and anticholinergic effects that make them specifically inappropriate for older adults, where they are associated with confusion, falls and urinary retention. They are not supplements and should not be bought as though they were.
Kava, and the melatonin dose problem
Kava has real anxiolytic evidence but has also been linked to severe hepatotoxicity, including cases requiring transplant, and is banned or restricted in several countries. Separately, high-dose melatonin is not dangerous in the way kava is, but doses of 5–20 mg deliver no advantage over 0.5–1 mg while reliably causing grogginess and vivid dreams. A blend that gives a combined total rather than a melatonin figure is hiding exactly the number you need.
Things that deserve caution rather than avoidance
Valerian is generally well tolerated but has rare reports of liver enzyme changes, and can leave residual sedation. 5-HTP should not be combined with SSRIs, SNRIs, MAOIs or triptans because of serotonin syndrome risk. Magnesium oxide is not unsafe, just poorly absorbed and laxative — a waste rather than a hazard.
Key ingredients to understand
The ingredients most relevant to this question, with what the evidence actually supports:
- Melatonin — Melatonin is the body's sleep-timing hormone, sold as a supplement mainly for jet lag and trouble falling asleep. It works best as a…
- Valerian — Valerian is the most popular herbal sleep aid. Meta-analyses suggest it may improve people's subjective sense of sleep quality, but it…
- 5-HTP (5-Hydroxytryptophan) — 5-HTP is a direct precursor to serotonin, taken for mood, sleep and appetite. It has some small supportive studies, but its serotonin activity…
- Magnesium — Magnesium is an essential mineral involved in hundreds of body processes, including nerve and muscle function, energy and blood-sugar control.…
Frequently asked questions
Is melatonin safe long term?
Short-term safety is good. Long-term data, particularly in children and adolescents where use has risen sharply, are limited. Use the lowest effective dose.
What about CBD for sleep?
Evidence is much weaker than the marketing suggests, product labelling is frequently inaccurate, and it interacts with drugs metabolised by CYP450 enzymes.
Are prescription sleeping tablets better?
They work, but carry dependence, tolerance and fall risk. Clinical guidelines put CBT-I first for chronic insomnia, ahead of both tablets and supplements.
Related on FactoWiki
- All health answers
- Ingredient evidence guides
- Melatonin — ingredient guide
- Valerian — ingredient guide
- How we review
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