Can't sleep at night
Trouble falling asleep, waking at 3am, light sleep: the common causes, when to see a GP, and what the trials say about magnesium, glycine and other sleep supplements.
What is usually behind it
Trouble falling asleep and waking in the small hours have different causes, and it helps to know which you have. Difficulty falling asleep is most often light, screens, caffeine after lunch, an irregular bedtime, or an overactive mind. Waking at 3am with a racing pulse is more often stress, alcohol, low blood sugar, or the hormonal changes of perimenopause. Both are made worse by a hot bedroom.
See your GP if poor sleep has lasted more than a month, if you snore heavily or stop breathing in your sleep, if you have low mood, or if you are relying on anything to get to sleep.
What the evidence says about supplements. Sleep hygiene and caffeine timing come first. Of the supplements, magnesium has the best trial evidence for sleep and works gradually: most measurable change by weeks two to four, a fair verdict at four to eight weeks (timeline); magnesium contributes to normal psychological function and the normal functioning of the nervous system. Glycine at 3 g an hour before bed showed better morning ratings from the first night in two small trials (glycine). Ashwagandha takes weeks, not days (ashwagandha). Melatonin is prescription-only in the UK. What to skip: twelve-ingredient sleep blends, which make it impossible to know what helped.
Next: Supplements for sleep · Nutri365, which reads your Oura sleep data alongside what you tell it.
Written by Nutri Tailor from the Health Reference Library. Last checked 6 September 2026. General information, not personal advice.