Why Can’t I Sleep? 7 Common Reasons for Poor Sleep

You go to bed tired, turn off the light, and suddenly your brain seems wide awake. Or perhaps falling asleep is easy, but you wake during the night or still feel exhausted the next morning.

Occasional poor sleep is common, but understanding what might be interfering with your sleep can make it easier to know where to start.

From stress and caffeine to your sleep schedule and evening light exposure, there are many reasons why a good night's sleep can sometimes feel surprisingly difficult.

In This Guide

• How much sleep do you actually need?
• 1. Stress and an overactive mind
• 2. Caffeine too late in the day
• 3. An inconsistent sleep schedule
• 4. Too much light in the evening
• 5. Alcohol before bed
• 6. Your sleep environment
• 7. Health and nutritional factors
• What can you do to sleep better?
• Can supplements help?
• Frequently asked questions

How Much Sleep Do You Actually Need?

Most healthy adults generally need at least seven hours of sleep per night, although individual sleep needs vary.

Sleep requirements change throughout life and can also differ between individuals. How you feel and function during the day matters alongside the number of hours you spend asleep.

Sleep quality matters too.

You can spend eight hours in bed and still wake up feeling tired if your sleep is frequently interrupted or poorly aligned with your body's natural sleep-wake rhythm.

Instead of focusing exclusively on a perfect number, it can be helpful to consider whether you wake feeling reasonably refreshed and can function well throughout the day.

1. Stress and an Overactive Mind

Stress can make it harder to fall asleep because your brain and body may remain in a heightened state of alertness when they should be winding down.

You've probably experienced it: you're exhausted all evening, but the moment your head hits the pillow, your mind starts reviewing conversations, tomorrow's tasks or problems you need to solve.

This is sometimes described as cognitive arousal – essentially, your brain remains highly active when you are trying to sleep.

Stress can also influence physiological systems involved in alertness and the body's stress response, making relaxation more difficult.

2. Caffeine Too Late in the Day

Your afternoon coffee may still be affecting you when you go to bed.

Caffeine promotes alertness primarily by blocking adenosine receptors. Adenosine is a chemical that gradually builds up during waking hours and contributes to your drive to sleep.

The effects of caffeine can last considerably longer than the initial feeling of energy.

Research has shown that caffeine consumed even several hours before bedtime can interfere with sleep. How quickly caffeine is metabolised also varies significantly between individuals.

And coffee is not the only source. Caffeine can also be found in:

• tea
• energy drinks
• cola
• pre-workout products
• some supplements
• chocolate

If you struggle to fall asleep, experimenting with an earlier caffeine cut-off can be a simple place to start.

3. An Inconsistent Sleep Schedule

Frequently changing when you sleep and wake can make it harder for your internal body clock to maintain a predictable rhythm.

Your body follows an approximately 24-hour cycle known as the circadian rhythm.

This internal clock helps regulate periods of alertness and sleepiness throughout the day and responds strongly to cues such as light, darkness, meals and activity.

If you wake at 6:30 during the week but sleep until 11:00 at weekends, your biological timing can shift – sometimes described as “social jet lag”.

You do not need to follow exactly the same schedule every day, but keeping your sleep and wake times reasonably consistent can help reinforce predictable sleep signals.

4. Too Much Light in the Evening

Bright light at night can signal to your brain that it is still daytime and delay the biological processes that prepare you for sleep.

Light is one of the strongest signals regulating your circadian rhythm.

As the environment becomes darker in the evening, your body normally begins increasing production of melatonin – a hormone involved in signalling biological night.

Bright artificial lighting and screens can interfere with this process, particularly when exposure occurs close to bedtime.

This does not mean you necessarily need to eliminate every screen after sunset.

A more realistic approach might include:

• dimming household lights in the evening
• reducing very bright screen exposure before bed
• avoiding scrolling in bed
• keeping your bedroom dark
• getting plenty of natural daylight earlier in the day

5. Alcohol Before Bed

Alcohol can make you feel sleepy initially while reducing sleep quality later in the night.

This is one reason alcohol can be misleading when it comes to sleep.

You may fall asleep more quickly after drinking alcohol, but sedation is not the same as healthy sleep.

As alcohol is metabolised during the night, sleep can become more fragmented. Alcohol can also affect normal sleep architecture and contribute to more frequent waking.

So if you regularly wake during the second half of the night after drinking, alcohol may be one factor worth considering.

6. Your Sleep Environment Is Working Against You

A bedroom that is too warm, bright, noisy or uncomfortable can make uninterrupted sleep more difficult.

Your environment provides your brain with signals about whether it is time to remain alert or rest.

A sleep-friendly bedroom is generally:

• dark
• quiet
• comfortably cool
• comfortable
• associated primarily with sleep and relaxation

Small changes can sometimes make a surprisingly noticeable difference.

Blackout curtains, reducing unnecessary light sources, adjusting room temperature or limiting disruptive noise can all help create a more consistent sleeping environment.

7. Health and Nutritional Factors

Sometimes poor sleep is connected to factors that cannot be solved simply by improving your bedtime routine.

Sleep can be affected by pain, hormonal changes, certain medications, mental health conditions and sleep disorders, among other factors.

Nutrition has also attracted increasing research interest.

For example, magnesium contributes to normal functioning of the nervous system and normal psychological function. Research has investigated whether magnesium status and supplementation may be related to sleep outcomes.

A systematic review examining magnesium and sleep found associations between magnesium status and sleep quality in observational research, although clinical intervention studies produced mixed results.

More recently, a 2025 randomised, placebo-controlled trial found that magnesium bisglycinate supplementation produced a small but statistically significant improvement in insomnia symptoms in adults reporting poor sleep.

However, this does not mean that nutrient deficiencies are the cause of most sleep problems or that taking a supplement automatically improves sleep.

If your sleep has changed significantly or problems persist despite healthy sleep habits, it is worth discussing this with a healthcare professional.

What Can You Do to Sleep Better?

Start with the behaviours that regulate your sleep-wake cycle rather than trying to change everything at once.

A simple sleep routine might look like this:

Trying to “force” yourself to sleep can sometimes make sleep feel even more stressful.

Instead, focus on creating the conditions that allow your natural sleep systems to do their job.

Can Supplements Help You Sleep Better?

Some supplements have been investigated for sleep, but they should complement healthy sleep habits rather than replace them.

Ingredients commonly researched in relation to sleep include magnesium, melatonin, glycine and L-theanine, although the strength and type of evidence differ considerably between them.

It is also important to distinguish between correcting an inadequate nutrient intake and taking additional nutrients despite already consuming sufficient amounts.

If you'd like to explore the evidence in more detail, read our guide to Which Supplements Can Support Better Sleep?

And if you're particularly interested in magnesium, our guide How Can Magnesium Bisglycinate Help You Sleep Better? takes a closer look at the latest research.

In Summary

If you find yourself asking, “Why can't I sleep?”, there may not be one simple answer.

Stress, caffeine, inconsistent sleep times, evening light, alcohol, your sleeping environment and underlying health factors can all interfere with healthy sleep.

The good news is that many of these factors are modifiable.

Rather than searching immediately for a quick fix, start by looking at your entire day: when you wake up, how much daylight you get, when you drink caffeine, how active you are, how you spend your evening and what your bedroom environment is like.

Healthy sleep is not just about what happens in the eight hours after you close your eyes. Your entire day helps prepare your body for the night ahead.

If sleep difficulties persist, significantly affect your daily life or occur alongside other symptoms, speak with a healthcare professional to investigate possible underlying causes.

Frequently Asked Questions

Why can't I sleep even though I'm tired?

Feeling physically tired does not always mean your brain is ready for sleep. Stress, mental stimulation, caffeine, evening light exposure and a disrupted sleep schedule can all contribute to feeling tired while still finding it difficult to fall asleep.

Why does my brain feel awake at night?

Stress, worry, stimulating activities and irregular sleep patterns can contribute to mental alertness at bedtime. Creating a consistent wind-down period before bed may help provide a clearer transition between daytime activity and sleep.

Why do I keep waking up during the night?

Night-time waking can have many causes, including alcohol, noise, temperature, stress, pain, hormonal changes and sleep disorders. Brief awakenings can also occur naturally between sleep cycles. Frequent or prolonged waking that affects your wellbeing should be discussed with a healthcare professional.

Can caffeine affect sleep even if I drink it in the afternoon?

Yes. Caffeine can remain active in the body for several hours, and people metabolise it at different rates. If you struggle to sleep, moving your last caffeinated drink earlier in the day may be worth trying.

Does using your phone before bed really affect sleep?

Evening light exposure can influence circadian signals involved in preparing the body for sleep. Phones can also keep you mentally stimulated. Reducing bright screens and stimulating content close to bedtime may therefore help some people wind down.

Can magnesium help if I can't sleep?

Magnesium contributes to normal nervous system and psychological function. Research into magnesium and sleep is still developing, with a recent magnesium bisglycinate trial finding a modest improvement in insomnia symptoms compared with placebo. It should not be considered a treatment for persistent sleep problems.

When should I see a doctor about poor sleep?

Consider speaking with a healthcare professional if sleep difficulties persist, regularly affect your daytime functioning, become significantly worse or occur alongside other symptoms. Persistent sleep problems can have many causes and may require individual assessment.

Scientific References

1. Watson NF, Badr MS, Belenky G, et al. (2015). Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Recommendation of the American Academy of Sleep Medicine and Sleep Research Society. Sleep, 38(6), 843–844.
2. Drake C, Roehrs T, Shambroom J, Roth T. (2013). Caffeine Effects on Sleep Taken 0, 3, or 6 Hours Before Going to Bed. Journal of Clinical Sleep Medicine, 9(11), 1195–1200.
3. Chang AM, Aeschbach D, Duffy JF, Czeisler CA. (2015). Evening Use of Light-Emitting eReaders Negatively Affects Sleep, Circadian Timing, and Next-Morning Alertness. Proceedings of the National Academy of Sciences, 112(4), 1232–1237.
4. Arab A, Rafie N, Amani R, Shirani F. (2023). The Role of Magnesium in Sleep Health: A Systematic Review of Available Literature. Biological Trace Element Research, 201, 121–128.
5. Schuster J, Cycelskij I, Lopresti A, Hahn A. (2025). Magnesium Bisglycinate Supplementation in Healthy Adults Reporting Poor Sleep: A Randomized, Placebo-Controlled Trial. Nature and Science of Sleep, 17, 2027–2040.

This article is for informational purposes only and is not intended to diagnose, treat, cure or prevent any disease. Food supplements should not be used as a substitute for a varied, balanced diet and healthy lifestyle.