Why Do You Feel Sleepy After Drinking Coffee

Adenosine and Sleepiness

Coffee is one of the most popular beverages and has been enjoyed as an energizer for centuries. But what is really behind coffee’s ability to energize and make us feel awake? Scientists have discovered that coffee’s effect on sleepiness results from a compound found within the coffee beans, called adenosine. Adenosine is a neurotransmitter, responsible for making us feel sleepy, and it is found naturally in all humans.
Adenosine works by binding to receptors in the brain, telling the body it’s time to rest or sleep. When a person consumes coffee, the adenosine levels increase, but in this case, instead of telling us to go to bed, the caffeine takes over. According to Dr. Matthew Walker, a professor of neuroscience and psychology at the University of California, Berkeley, caffeine works as an “antagonist” to the adenosine receptors, blocking the signals sent to the body instead, allowing increased focus and alertness. Essentially, when we drink coffee, our adenosine levels increase, but because of the caffeine, the adenosine receptors don’t initiate the usual sleepiness.

Caffeine & Sleepiness

But we can’t ignore the fact that caffeine can cause sleepiness. Consumer Reports notes that 200 milligrams of caffeine can cause “developed tolerance”, leading to sleepiness if you aren’t used to ingesting caffeine regularly, because your body is expecting more than what it’s actually getting.
Sleep deprivation can also lead to an increased risk of sleepiness, regardless of how much caffeine you’ve consumed. Dr. Pavel Ovsiannikov, a board-certified sleep specialist and Fellow of the American Academy of Sleep Medicine, issued a press release in which he noted that “not getting enough sleep increases our chances of feeling tired and sluggish, regardless of whether or not we have coffee.” A lack of sleep will also increase the chances of feeling drowsy after drinking coffee.

Tolerance & Sleepiness

Tolerance also plays a role in how coffee affects our sleepiness levels. Dr. Walker stated that remaining moderate or decreasing the amount of coffee consumed is the “only way to break out of the tolerance trap.” Which means, if you’re drinking multiple cups of coffee per day, reducing the intake can restore the energy you felt when first drinking the coffee. So, if you’re not feeling energized or awake after having your morning cup, it may be time to consider cutting back or tapering to a lower dose of caffeine.
Experts suggest that regular coffee drinkers should focus on consuming quality coffee, rather than quantity. Robert H. Shmerling, MD, a faculty editor of Harvard Health Publishing suggests that “If you’re seeking better-tasting coffee, you may settle for less caffeine than you could get with a different brand.”

Slow Metabolism and Sleepiness

Another factor in feeling sleepy after drinking coffee is your metabolism. If you have a slow metabolism, then you may find it more difficult to remain alert after drinking coffee because it takes the body longer to process the caffeine. Similarly, if your body has already had caffeine on a regular basis, your caffeine tolerance may be higher, making it difficult to feel the effects after a cup of coffee.
Furthermore, other habits, such as smoking, can also make you feel sleepy after drinking coffee. According to a study by the Prehospital and Disaster Medicine Journal, those who engage in smoking and drinking coffee can increase their chances of feeling drowsy and sleepy. The study also noted that although research has yet to confirm, this could be due to the effects of nicotine and caffeine working against each other when combined together.

Caffeine Tolerance & Sleepiness

Caffeine tolerance also plays a role. A study by the Sleep Medicine Journal revealed that people with a higher level of caffeine tolerance felt more alert after drinking coffee. The study showed that those with lower caffeine tolerance felt more drowsy and less alert — even after drinking coffee.
The study also examined the effects of caffeine on circadian rhythms and found that the consumption of caffeine can affect sleeping patterns, making it harder to get a good night’s sleep. This is important to consider because insomnia can have an effect on caffeine consumption: those with insomnia might consider avoiding caffeine in the afternoon or evening in order to sleep better at night.

Mild Stimulation & Sleepiness

There’s also the idea that some people simply find coffee to be a mild stimulant. As suggested by Baylor College of Medicine and WebMD, this means that for those individuals, the “potency” of the caffeine within the coffee does not lead to an invigorated feeling, but rather one of mild stimulation — which could in turn lead to feeling a bit sleepy.
This doesn’t mean that people should avoid coffee altogether. In fact, drinking it in moderate amounts can be beneficial. Coffee can help to improve focus, concentration, and mood. It can also help with physical activities such as running and playing sports. Thus, individuals who do not experience a caffeine boost may still find it beneficial to drink coffee because of its ability to provide mental clarity.

Coffee & Adrenaline

Coffee can also make people feel more alert because it causes the release of adrenaline. According to scientists at Rutgers University, caffeine stimulates the release of adrenaline which can act as an energizing hormone. Adrenaline is released in response to stress, and it can trigger a number of bodily functions, such as increasing the heart rate and blood pressure, as well as giving people a burst of energy.
Although this energy boost can be beneficial, Dr. Walker advised that working too hard or in an anxious state can also lead to an increase in cortisol levels, which is known to make people feel more tired. Keeping this in mind, it’s clear that using coffee as an energy enhancer should be done in moderation to ensure maximum efficacy and avoid fatigue.

Coffee & Stress

Coffee is often used as a way of managing stress, but in reality, it can increase stress levels. Coffee stimulates the release of the stress hormone cortisol, which can lead to feelings of anxiety and restlessness.
When cortisol is released in small amounts, it can help the body to cope with stressful situations. However, in order to keep cortisol levels within a healthy range, people should avoid drinking too much caffeine, as it can lead to an excess of cortisol being released. This can lead to feelings of anxiety and restlessness, which can cause us to feel sleepy.
Coffee is also known to trigger a release of adrenaline, as mentioned before. Too much adrenaline can lead to a “crash” afterwards, leaving us feeling tired and drained.

Coffee & Sleep Deprivation

It’s also important to consider the effects of sleep deprivation when drinking coffee. Being sleep-deprived puts an immense amount of strain on the body and can cause exhaustion and drowsiness. These effects can be exacerbated when coffee is consumed as well, as coffee can block the body’s natural urge to sleep, creating a vicious cycle.
The American Academy of Sleep Medicine suggests that drinking coffee can lead to caffeine-withdrawal symptoms if too much is consumed — even if it’s consumed too frequently instead of all at once. The academy notes that caffeine-withdrawal symptoms can include “fatigue, impairment of reaction time and cognitive performance, cognitive distortion and lowered mood and fatigue.”


Summarizing, it can be concluded that sleeping after drinking coffee is a complex interaction between physical and psychological factors. Adenosine receptors and caffeine are responsible for energy levels, whereas our metabolism and lifestyle, as well as our tolerance for caffeine can influence the way our body responds to this popular beverage. Furthermore, caffeine can cause sleep deprivation and an excessive release of hormones — like adenosine, adrenaline and cortisol — that can make us feel sleepy.
Finally, drinking coffee should be done in moderation to ensure maximum efficacy and avoid fatigue.

James Giesen is an avid coffee enthusiast and a prolific writer. His focus on coffee has led him to write extensively about the brewing, roasting, and tasting of this beloved beverage. He has been working in the Specialty Coffee Retail industry for over five years.

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