Falling asleep and staying asleep are different problems
Some nights refuse to start: the light goes off, you are tired, and your brain simply declines the invitation. Other nights start perfectly and then break at 3am. From under the duvet these feel like one problem, called bad sleep. Physiologically they are two, run by largely separate systems, and knowing which one is yours changes what is actually worth trying.
What has to happen before you can fall asleep?
Falling asleep is something your body permits, once three conditions line up. You do not will it.
The first is sleep pressure. A compound called adenosine accumulates in the brain for as long as you are awake, a by-product of the day's energy use, and it is a large part of the heavy-eyed feeling that builds through the evening [2]. Caffeine works mostly by sitting in adenosine's receptors and muting that signal, and because its half-life is around five hours [7], a 4pm coffee is still doing that at ten. If you want the timing in detail, we have written about when to stop drinking caffeine before bed.
The second is timing. Your body clock runs a daily programme of alertness that does not much care when you would like to sleep. Through the day it actively props you awake; in the late evening it eases off and opens a gate. Try to sleep well before your gate opens, perhaps because tomorrow starts early, and you are pushing against the programme instead of riding it.
The third condition is the one most people have never heard of: heat loss. Core body temperature falls in the evening as part of the same clock programme, dropping by around a degree across the night [1], and sleep tends to begin while that curve is falling steeply. The body sheds this heat through the skin, particularly the hands and feet, which is why they warm up as you get sleepy. In one frequently cited study, the warming of hands and feet was among the strongest predictors of how quickly people fell asleep [1]. It is also why a warm bath an hour or two before bed can genuinely help: the after-effect of warming the skin is a faster drop in core temperature once you get out.
Lying awake at bedtime usually means one of these three has not arrived: too little pressure, the wrong point on the clock, or a body still running warm and alert.
What keeps you asleep once you are under?
Staying asleep is a different project, and the conditions change as the night goes on. The night is built from cycles of roughly ninety minutes, and the cycles are not all alike. Deep, slow-wave sleep is concentrated in the first half of the night; the second half is dominated by REM and lighter stages [2]. This front-loading means the early hours of the morning are, by design, the shallowest part of your sleep.
Whether you stay under through that shallow stretch depends on the systems that could wake you staying quiet. Sleep pressure has largely been spent by then. Core temperature is at its lowest and beginning to turn. Cortisol, the body's principal alerting hormone, starts its climb in the early hours as part of the normal preparation for waking [6]. Sleep maintenance is a balance: a lighter sleep state on one side, and everything that might tip you into wakefulness on the other.
Why 3am, specifically?
Brief waking is normal. Most people surface momentarily between cycles several times a night and simply do not remember it [4]. The 3am problem lies in what happens after the waking.
By the small hours the conditions are stacked. Sleep is at its lightest, the pressure that would pull you straight back under is mostly spent, and the alerting system is beginning to stir. A wake that would have lasted seconds at midnight now has room to take hold, and if the mind switches on, on cue, with tomorrow's list or today's regrets, wakefulness feeds itself.
Several everyday things widen that opening. Alcohol is the classic: it shortens the time to fall asleep, then fragments the second half of the night as it is metabolised [5]. A warm bedroom works against the low-temperature trough that stable sleep prefers. Stress raises the baseline of the very alerting system that is already scheduled to rise. None of this is rare or strange: regular night-time waking is one of the most commonly reported sleep complaints, and it affects roughly a third of adults [4].
If that is the shape of your nights, we have written separately about why you wake up at 3am and what genuinely helps you get back to sleep.
Why does one product rarely fix both?
Because the two problems ask for different help. Support for sleep onset is about the transition: quieting arousal and encouraging the evening heat dump. Glycine is a good example of how specific this gets: in one small trial, around three grams before bed improved self-rated sleep quality and shortened the measured time to fall asleep [3]. That is onset physiology, targeted directly. We have since examined what the glycine evidence actually shows, and who funded it.
Support for sleep maintenance asks a different question: what the body needs so that the systems keeping sleep stable can hold through its shallowest hours. The job is different, and so are the emphasis and the doses.
A single all-purpose formula has to split the difference, and usually ends up doing neither job at the dose the research actually used. This split is why Verina makes two formulas, Fall Asleep and Stay Asleep, rather than one, and that is the only selling this article will do. The physiology above is true whether or not you ever buy anything.
Common questions
Is waking in the night always a problem?
No. Brief waking between sleep cycles is part of normal sleep, and most of it is never remembered. It becomes worth attention when you regularly cannot get back to sleep, or when your days are suffering for it.
Should I get out of bed if I cannot sleep?
The standard advice from behavioural sleep medicine is yes: if you have been awake long enough to become frustrated, get up, keep the lights low, do something quiet and dull, and come back when you feel heavy. It protects the association between your bed and being asleep, and stops you lying there teaching yourself the opposite.
When is it a matter for a GP?
Loud snoring, gasping or pauses in breathing point towards sleep apnoea, which no supplement addresses. Months of struggling most nights, with real daytime impairment, points towards insomnia disorder, where structured behavioural treatment is the first line. Both are conversations for a GP, not a shop.
Can you have both problems at once?
Yes, and plenty of people do: slow to switch off and broken later on. Even then it helps to think of the night as two jobs, because the things that help each half are not the same.
References
- Kräuchi K, Cajochen C, Werth E, Wirz-Justice A. Warm feet promote the rapid onset of sleep. Nature, 1999.
- Borbély AA. A two process model of sleep regulation. Human Neurobiology, 1982.
- Yamadera W, Inagawa K, Chiba S, et al. Glycine ingestion improves subjective sleep quality in human volunteers. Sleep and Biological Rhythms, 2007.
- Ohayon MM. Nocturnal awakenings and comorbid disorders in the American general population. Journal of Psychiatric Research, 2008.
- Ebrahim IO, Shapiro CM, Williams AJ, Fenwick PB. Alcohol and sleep I: effects on normal sleep. Alcoholism: Clinical and Experimental Research, 2013.
- Mohd Azmi NAS, et al. Sleep and circadian regulation of cortisol: a short review. Current Opinion in Endocrine and Metabolic Research. 2021;18:178-186.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on the safety of caffeine. EFSA Journal. 2015;13(5):4102.