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December 27, 2023 4 min read

Why Does Coffee Make You Tired?

Sleep deprivation, caffeine tolerance, dehydration, adenosine levels, blood sugar changes, or individual differences in caffeine metabolism may cause you to feel tired after drinking coffee.

Sleep Deprivation

More than one-third of Americans re sleep-deprived and not receiving the recommended minimum of seven hours of sleep per night. Although coffee can provide a quick pick-me-up, it is not an adequate substitute for sleep. Sleep deprivation can reduce alertness  Slow down response times, and negatively affect thinking.

Drinking more coffee in an effort to overcome tiredness might backfire. Ingesting too much caffeine can negatively impact sleep , making you sleepy the next day. As a result, turning to coffee to fix the effects of sleep deprivation can create a negative cycle. Because you feel more tired, you drink more coffee, but that coffee disrupts your sleep, leading to more tiredness in the long run.

Caffeine Tolerance

Rather than making you tired, it is possible that coffee simply is not making you as alert as it once did.

Initially, consuming caffeine can improve your mood and reaction times s well as your physical performance  However, similar to the way people can develop a tolerance for alcohol, those who consume caffeine regularly develop a tolerance to it. As a result, consuming the same amount of caffeine will not produce the same positive effects over time, and consuming more coffee to try to recuperate its positive effects could have negative effects for your sleep.

Additionally, regular caffeine use over just three days is enough to spark withdrawal symptoms when you stop consuming it, including an increased feeling of tiredness.




Coffee is considered a diuretic , which means it can increase your need to urinate and lead to fluid loss. If these bathroom trips wake you up throughout the night, you might feel more tired the next day. Additionally, mild dehydration itself can cause you to experience fatigue . Mild dehydration can also decrease cognitive performance, impair memory, and increase anxiety and tension.

Coffee may be more likely to affect hydration for people who are not regular coffee drinkers , and it may have little to no effect until a certain level of caffeine is reached.

Blood Sugar Changes

Drinking coffee in the morning may contribute to insulin resistance and negatively impact your body’s ability to tolerate glucose . This makes you more sensitive to sugar or carbohydrates found in your drink or breakfast, and it can cause a temporary surge in blood sugar. Most common in people with diabetes or prediabetes, high blood sugar levels are associated with increased feelings of fatigue , particularly in women.

Even if your blood sugar does not reach clinically high levels, you might feel increased tiredness due to low blood sugar after your blood sugar levels decrease. In the hours after consuming sugar, blood sugar levels peak and then dip, and this falling blood sugar may affect your energy levels.

If you believe you have diabetes or other blood sugar problems, make an appointment with your doctor.

Adenosine Levels

Released in larger quantities when we are sleep-deprived , adenosine is a key chemical that helps bring on sleepiness . Coffee promotes alertness and reduces tiredness by blocking adenosine receptors and preventing the chemical from exerting its sleep-promoting effects. However, research suggests that the body compensates for this effect by increasing sensitivity to adenosine. Once the effects of the coffee wear off, the resulting surge can cause sleepiness and muscle fatigue 

Caffeine Metabolism

Not everyone metabolizes caffeine at the same rate. If you metabolize caffeine slowly, it might not make you feel alert as quickly as it does for other people. Conversely, if you metabolize caffeine quickly, it might not impact you as much or it might wear off more quickly, leading to feelings of sleepiness sooner.

Multiple factors impact how quickly a person metabolizes caffeine. Smoking cigarettes speeds up caffeine metabolism. By contrast, conditions such as pregnancy or liver disease might slow down caffeine metabolism.


Although more research is needed, researchers have found that genetics impact how an individual responds to caffeine. Having specific genes could make you more sensitive to caffeine’s negative effects, such as anxiety or sleep disruption. If ingesting caffeine negatively impacts your sleep, you might experience increased daytime tiredness as a result.

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