Melatonin Side Effects: Understanding Nightmares, Vivid Dreams and Other Sleep Aid Risks

At 3am, James Nardell was jolted awake by his own screams.

His wife sprang out of bed and switched on the light, fearing something was seriously wrong. James was physically safe, but in the dream he had just been fleeing for his life from a crowd of zombies.

The nightmare had seemed frighteningly lifelike.

Eventually, his wife managed to calm him down, teasing that he might need to ‘stop watching so many zombie shows’. James, however, thought he knew what else could be behind the episode.

The unsettling dreams had started after he began using melatonin, a supplement taken to improve sleep.

James’s sleep difficulties began in 1999, after he moved from Somerset, England, to Bangkok to work in affiliate marketing. Although he was based in Thailand, he continued working with US companies, forcing him to cope with a 12-hour time difference and a schedule of late nights followed by early mornings.

Like many of the estimated 30 million Americans with insomnia, James says his main challenge was getting to sleep in the first place.

‘I just don’t seem to be able to turn off my thoughts when I go to bed,’ he tells Our News Outlet. ‘Before melatonin, I tried a few things. They worked to get me to sleep, but the next day I’d be groggy, and that’s no good for a 6am client call where I must be sharp.’

In 2018, James’s wife mentioned his sleep problems to a colleague during a business trip to Singapore. The colleague recommended melatonin, and she brought a bottle home for him to test.

James started taking it three or four nights a week, especially when he had an important early meeting the next day.

The supplement did help him fall asleep. Before long, though, he noticed a striking change in his dreams on the nights he used it. They became intensely vivid, sometimes leaving him drenched in sweat, disoriented and aware of his heart racing.

‘I rarely remember my dreams – they’re not particularly intense,’ he says. ‘But with melatonin, they really can be.’

Then, in 2020, melatonin produced another unwelcome effect: what James calls a ‘melatonin hangover’ the next morning.

‘When it happened, it lasted until lunchtime – I felt heavy-headed, slow and couldn’t focus properly on work no matter how hard I tried,’ he says.

The irony was that he felt even more drained than after a night of poor sleep. James suspected that particular bottle might have been counterfeit because he had bought it online and noticed that its label looked slightly unusual. He had never experienced the same reaction with melatonin before.

James’s story, however, is not an isolated one.

Melatonin is a hormone the brain releases in the evening. It helps regulate the body’s internal clock, signaling that night has arrived and prompting feelings of drowsiness.

Manufactured melatonin is also widely sold as a dietary supplement, fueling a rapidly expanding US market aimed at millions of people searching for better sleep.

Consumers can now choose from pharmacy shelves stocked with tablets, capsules, flavored gummies and liquids, often available in a confusing array of doses and strengths.

That’s markedly different from countries including the UK, where it’s available only on prescription.

Today, more than one in four Americans now report taking melatonin to help them sleep.

Yet experts now warn that many may be taking far more than they need by regularly consuming high-strength supplements commonly sold in stores – and this could be putting them at risk of bizarre sleep disturbances and other unpleasant side effects, from horrific nightmares and waking hallucinations to a debilitating next-day ‘hangover.’

So how can something designed to help you sleep sometimes make the night an ordeal – and how much should you really be taking? 

Part of the answer lies in the fact that melatonin works differently from conventional sleeping pills. Rather than simply sedating the brain, it acts primarily on the body’s internal clock.

Levels of the hormone naturally begin to rise in the evening as darkness falls, binding to receptors in the brain that signal that night has begun and helping the body prepare for sleep.

Taking synthetic melatonin can reinforce this signal, making you feel drowsier and helping you fall asleep.

And evidence suggests surprisingly little extra melatonin may be needed to produce an effect.

Studies have found doses as low as 0.3mg can have an impact in adults – a fraction of the 5mg James was taking several nights a week, or the 10mg to 20mg doses readily available on US pharmacy shelves.

Crucially, say experts, a bigger dose does not necessarily produce a better night’s sleep.

Taking substantially more than the body needs can instead cause melatonin levels in the blood to soar far above those produced naturally. Some research suggests doses of between 1mg and 5mg can produce levels up to 100 times higher than the body’s normal night-time peak.

And because the hormone can remain circulating for hours, particularly at higher doses, elevated levels may persist after a person wakes.

‘Once you’ve taken enough melatonin to produce that sleep signal, taking several times more doesn’t necessarily make that signal more effective,’ says Dr Jordan Burns, chiropractor and sleep coach for Amerisleep. 

What it can do is leave much higher levels of the hormone circulating in your body for longer, which may leave you feeling groggy, dizzy or headachy the next day, Burns said.

And the higher the dose, the greater the risk appears to be. A major review of studies involving doses of 10mg or more found these side effects were about 40 per cent more common among people taking melatonin than those given a placebo.

But some of the most unsettling effects can occur while users are asleep. 

Intense dreams and nightmares have been reported by people taking melatonin – including James – and scientists believe the hormone’s effects on the stages of sleep in which we dream may help explain why.

Rapid eye movement – or REM – sleep is the stage of the night when the brain becomes highly active and our most vivid, elaborate dreams typically occur.

Studies suggest melatonin can increase the amount of time spent in REM sleep and make periods of REM more continuous. In theory, this could mean longer, more intense dreams – and make frightening ones feel particularly real.

However, researchers have not yet proved that this is the reason melatonin users experience nightmares, and it remains unclear why some people appear particularly susceptible.

More disturbing still, some melatonin users on social media have reported hallucination-like experiences – seeing people, shapes or objects that weren’t really there, sometimes shortly after waking.

Some have even dubbed the phenomenon ‘melatonin psychosis’ – although this is not a recognized medical condition.

One such user is Annalise, who said on TikTok that she had been ‘seeing things’ for five days after she began taking the supplement.

‘The other day my cat walked into the room, but I thought I saw a human walking into the room,’ she says in the social media clip, which has now been viewed more than 36,000 times. ‘The same with my friend’s chihuahua – I thought it was a human.’

The experiences were so convincing that she began researching the early symptoms of schizophrenia.

‘I thought, ‘Why do I keep seeing things?” she says. ‘I thought I was going crazy.’

And similar accounts can be found across Reddit. One user describes taking melatonin before suffering a night of fragmented sleep and vivid nightmares, during which she felt she was never ‘truly’ asleep.

In one episode, she dreamed about her brother before opening her eyes – only to apparently see him standing beside her bed.

‘Even though I knew I was facing the wall, I was seeing my brother standing next to my bed in a doorway,’ she writes. ‘I closed my eyes and when I opened them again I hallucinated him walking out the door.’

While alarming, experts stress that experiences like these are not evidence that melatonin is causing psychosis.

Instead, they may be hypnagogic or hypnopompic hallucinations – vivid sights, sounds or sensations that occur as someone is falling asleep or waking up, when elements of a dream can appear to spill into consciousness.

‘There’s a blurry period between dreaming and waking when dream-like experiences can feel incredibly vivid and real,’ says Burns.

‘Melatonin doesn’t directly cause hallucinations, as far as we know. But because it can make dreams more vivid, it may make those experiences during the transition between sleep and wakefulness feel much more intense.

‘You might wake up and, for a few moments, still see or hear something from a dream. It can feel completely real, but that’s very different from hallucinating while you’re fully awake.’

Intriguingly, some research has even suggested melatonin may help reduce hypnagogic and hypnopompic hallucinations in people who already experience them. 

There may also be another explanation for why some people experience unexpectedly powerful effects from melatonin: the dose they swallow may bear little resemblance to the number printed on the bottle. 

Unlike prescription medicines, melatonin is regulated in the US as a dietary supplement – meaning products are not subject to the same controls over their contents.

In one striking analysis of 31 commercially available supplements, researchers found the actual amount of melatonin ranged from 83 per cent below the dose stated on the label to nearly five times the advertised amount.

Levels could also vary dramatically between different batches of the same product, while more than a quarter contained serotonin – a powerful brain chemical that was not declared on the label.

A more recent US study of melatonin gummies produced similarly alarming results: 22 of the 25 products tested contained a different amount from that advertised, with some delivering more than three times the stated dose.

In other words, someone carefully choosing what they believe is a modest dose may unwittingly be taking several times that amount.

So what should you do if melatonin isn’t giving you the restful night’s sleep you hoped for?

Experts say the answer is not simply to increase the dose. Anyone regularly waking exhausted, suffering disturbing dreams or finding their insomnia persists despite taking melatonin should speak to a doctor about what may be disrupting their sleep.

For persistent insomnia, the treatment with considerably stronger evidence is cognitive behavioral therapy for insomnia, or CBT-I – a structured program designed to change the thoughts, behaviors and sleeping patterns that perpetuate the condition.

James, meanwhile, still takes melatonin occasionally, but far less frequently than before. He says regular exercise has proved a better way of improving his sleep.

‘Maybe use melatonin when you really have to, but otherwise try to fall back on better methods,’ he says.

And after his experience with the suspicious pills, he is now far more careful about where his supplements come from.

‘I only get melatonin from family and colleagues who bring it back from Singapore or the US, bought from proper pharmacies,’ he says.

‘I won’t buy supplements from an online marketplace again. If a label looks off, I don’t take the chance.’