Is Over-the-Counter Melatonin as Harmless as People Think?

“It’s natural.”
“You can’t overdose.”
“It’s not a drug—it’s a supplement.”

These are the common justifications patients offer before reaching for a bottle of melatonin.

In pharmacies across the globe, melatonin is marketed as a gentle, non-addictive sleep aid—a seemingly harmless shortcut to dreamland. But, as with most things in medicine, the story is more nuanced. While melatonin is indeed a naturally occurring hormone, over-the-counter (OTC) use is often anything but natural, harmless, or well-regulated.

This article explores the deeper science, widespread misconceptions, and hidden risks behind casual melatonin use—especially relevant for doctors, pharmacists, and medical students constantly fielding patient questions about it.

Melatonin: The Basics

Melatonin is a hormone produced by the pineal gland in response to darkness. It plays a key role in regulating the circadian rhythm—the body’s internal 24-hour clock. Its secretion acts as a signal to the body that it’s time to wind down and prepare for sleep.

Under normal physiological conditions, melatonin levels:

• Begin rising in the evening
  
  
• Peak between 2–4 AM
  
  
• Decline toward the early morning hours

In theory, melatonin supplementation can help patients experiencing:

• Jet lag
  
  
• Shift work disorder
  
  
• Delayed sleep phase syndrome
  
  
• Pediatric sleep disorders, particularly in neurodevelopmental conditions like ADHD or autism

But this simplistic view of “just take melatonin and sleep better” is misleading.

The Problem with “Over-the-Counter” Status

In many countries—particularly the United States—melatonin is sold as a dietary supplement rather than a pharmaceutical. This classification means:

• It’s not subject to the same rigorous regulatory oversight as prescription medications
  
  
• The purity, potency, and consistency of different products can vary dramatically
  
  
• Labeling may not reflect the actual contents

In contrast, some countries, like the UK, restrict melatonin to prescription use, acknowledging the need for greater oversight.

A 2017 study in the Journal of Clinical Sleep Medicine revealed that melatonin content in OTC products varied from -83% to +478% of the labeled dose. Disturbingly, some products even contained serotonin—posing serious risks for serotonin syndrome and other complications.

Are People Taking Too Much?

In most cases, yes.

Normal nighttime physiologic melatonin levels in plasma range between 10 and 80 picograms/mL. However, a single 3 mg OTC tablet can elevate levels to 1,000–3,000 pg/mL—up to 100 times higher than what the body would naturally produce.

This is akin to using a fire hose to water a houseplant.

Excessive dosing not only lacks additional benefit—it may paradoxically reduce efficacy. Over time, high doses may desensitize melatonin receptors, diminishing the hormone’s action and potentially disrupting circadian rhythms even further.

Who Actually Benefits from Melatonin?

Evidence-based indications for melatonin use are narrower than the general population believes. Proven benefit exists in:

• Jet lag: Helps with realignment of the sleep-wake cycle when traveling across time zones
  
  
• Delayed sleep-wake phase disorder: Can shift circadian timing forward in patients with sleep onset delay
  
  
• Pediatric neurodevelopmental disorders: May help improve sleep initiation and duration in conditions like autism spectrum disorder or ADHD

But for the average adult struggling with sleep due to stress, irregular schedules, or anxiety, melatonin’s impact is modest at best.

Side Effects That Are Overlooked

Despite its reputation as a safe supplement, melatonin does come with potential side effects, especially with long-term or high-dose use. These include:

• Daytime sleepiness or grogginess
  
  
• Vivid dreams or nightmares
  
  
• Mood disturbances, such as irritability or low mood
  
  
• Hormonal imbalances—particularly concerning in adolescents
  
  
• Headaches, dizziness, nausea, or gastrointestinal upset

Notably, most clinical trials evaluating melatonin use are short-term. There’s a glaring absence of robust long-term safety data—particularly in healthy populations using melatonin daily for years.

What About Children and Teenagers?

This is perhaps the most worrisome trend. Many parents routinely give melatonin to children and adolescents, assuming it’s a safer alternative to antihistamines or prescription sleep aids. Common justifications include:

• It’s “natural” and therefore benign
  
  
• It helps reduce sleep problems related to excessive screen time
  
  
• It’s non-habit forming

However, chronic use in children could interfere with natural hormone cycles. There’s growing concern that long-term melatonin supplementation may:

• Disrupt puberty onset and progression
  
  
• Alter gonadal axis regulation
  
  
• Affect hormonal rhythms critical for development

While melatonin can be appropriate in certain pediatric neurodevelopmental contexts, it must never be used as a substitute for consistent bedtime routines, screen limitation, and behavioral sleep interventions.

Melatonin Isn't a Sedative

A critical misconception is that melatonin is a sedative-hypnotic. It is not.

Unlike drugs like zolpidem or benzodiazepines, melatonin doesn’t knock a person out. Instead, it nudges the body to initiate its natural sleep cascade.

Patients expecting rapid-onset sedation will be disappointed—and are misunderstanding the mechanism. When used correctly, melatonin should be taken 30–60 minutes before the desired bedtime, ideally timed to reinforce circadian alignment rather than override it.

Melatonin and Drug Interactions

Melatonin interacts with a variety of medications, which is particularly important in polypharmacy cases such as geriatric patients. Key interactions include:

• Anticoagulants/antiplatelets: Potential to increase bleeding risk
  
  
• Immunosuppressants: Melatonin may stimulate immune activity, counteracting immunosuppression
  
  
• Antidepressants: Potential risk for serotonin syndrome, especially with SSRIs or SNRIs
  
  
• Antihypertensives: May exacerbate hypotensive effects

This interaction profile makes casual, unsupervised use problematic—especially in medically complex patients.

Quality Control and Hidden Contaminants

Due to its supplement status, melatonin is not held to the same manufacturing standards as pharmaceuticals. This opens the door to:

• Contamination with unwanted substances like serotonin or other hormones
  
  
• Batch-to-batch inconsistency in dosage strength
  
  
• Addition of unlisted ingredients or fillers

Healthcare professionals recommending melatonin should advise pharmacy-grade products or those independently tested for purity and accuracy. Products used in clinical trials often differ significantly from what’s found on supplement store shelves.

The Placebo Effect is Real (and Powerful)

Many patients report subjective improvement with melatonin—and this shouldn’t be dismissed.

Even when studies show an average sleep onset reduction of only 7–10 minutes, that psychological benefit can still translate into a meaningful improvement in perceived sleep quality. The placebo effect, particularly in sleep medicine, is strong and clinically relevant.

That said, physicians should focus on first-line approaches such as cognitive-behavioral therapy for insomnia (CBT-I), which has more robust, long-term efficacy than any supplement.

Safer Alternatives to Explore First

Before reaching for melatonin, patients should be encouraged to optimize foundational sleep practices:

• Establish consistent sleep and wake times, even on weekends
  
  
• Limit screen exposure at least 1–2 hours before bed
  
  
• Create a quiet, dark, and cool sleep environment
  
  
• Avoid caffeine and heavy meals before bedtime
  
  
• Use mindfulness, meditation, or breathing techniques to wind down
  
  
• Consider CBT-I if insomnia is persistent or stress-related

These non-pharmacologic strategies offer durable, evidence-based improvements in sleep health—without the hormonal manipulation.

When to Avoid Melatonin Altogether

Melatonin should not be used in certain populations without explicit medical supervision. Avoid or exercise caution in:

• Pregnant or breastfeeding women (safety data lacking)
  
  
• Patients with autoimmune diseases (melatonin may modulate immune responses)
  
  
• Individuals with seizure disorders (potential risk of lowering threshold)
  
  
• Polypharmacy patients, especially elderly or those on interacting medications
  
  
• Anyone using melatonin daily for extended periods without reassessment

Doctors should emphasize that melatonin is not intended as a long-term sleep solution unless clearly indicated.

So… Is It Harmless?

In short: not entirely.

When used in short-term, low-dose, properly timed situations for specific sleep-related disorders, melatonin is relatively safe. But its casual, high-dose, long-term use—especially in children or medically complex patients—raises important safety and ethical concerns.

As clinicians, we must reinforce that:

• “Natural” does not equate to safe
  
  
• Hormones are not interchangeable with vitamins
  
  
• Sleep issues are rarely resolved with a pill alone

Melatonin has its place—but only when used judiciously, appropriately, and with a solid understanding of its pharmacologic nature.