Coffee contains caffeine, which increases alertness by stimulating the nervous system. However, its effects vary depending on individual differences, as well as how much and how often you consume it. So, some people may still feel sleepy even after consuming caffeine.

Caffeine makes you feel awake because it blocks adenosine receptors in your brain. Adenosine is a chemical that builds up as your body uses energy during the day, telling your brain it’s time to rest. When caffeine blocks these signals, your brain doesn’t realize you’re tired—even if your body is. Eventually, this can lead to:

• Caffeine crash: Caffeine doesn’t last forever. After a few hours, it wears off and adenosine can finally attach to its receptors. This sudden flood of “tired” signals causes a “caffeine crash.”
• The cycle of tiredness and caffeine: If you didn’t sleep well, you may need caffeine in the morning. But when it wears off, you feel sleepy againwhich can make you reach for more caffeine. This can turn into a cycle of coffee and fatigue.
• Tolerance to caffeine: If you drink caffeine every day, your body gets used to it. Over time, it won’t make you feel as alert as before, so you might drink more to get the same effect. But higher doses overstimulate your nervous system, which can hurt your sleep and health.

Caffeine, especially when consumed close to bedtime, can cause problems with sleep quality and duration, leading to increased sleepiness.

However, not everyone feels caffeine’s impact in the same way. Many factors influence how your body responds to caffeine, including but not limited to:

• Genetics: Your genetics can affect how quickly your body breaks down caffeine and how sensitive you are to it.
• Medication use: Some medications affect how you break down caffeine. They can speed up or slow down caffeine metabolism. For example, birth control pills slow caffeine breakdown, so caffeine stays in your bloodstream longer.
• Health status: Health conditions can affect caffeine breakdown. For example, people with liver conditions may have a slower caffeine breakdown.
• Pregnancy: Caffeine breakdown slows during pregnancy, and overconsumption is linked to health risks for both the pregnant person and their baby.
• Smoking: Smoking speeds up caffeine breakdown, causing your body to eliminate caffeine faster.

Many factors can cause daytime sleepiness, including but not limited to:

• Hydration: When you don’t consume enough water, you become dehydrated. Since water is essential for every system in the body, it also impacts sleep. A study showed that adequate fluid intake was linked to deep sleep during the night and improved sleep quality.
• Medication use: Some medications, such as allergy medications, pain medications, and antidepressants, can cause sleepiness as side effects. Also, some over-the-counter medications contain caffeine.
• Health conditions: Excessive daytime sleepiness can be a sign of health conditions, such as insomnia, sleep apnea (breathing disorder), sleep walking, and circadian rhythm disorders. Conditions like anemia (low red blood cell count) and hypothyroidism (underactive thyroid) can also cause sleepiness.
• Environment: Light exposure at night can disrupt the natural sleep-wake cycle. For example, people working night shifts may experience sleepiness.
• Nutrient deficiencies: Nutrients play an essential role in energy production. Deficiencies in vitamins and minerals can cause low energy and fatigue.

Post-coffee fatigue is likely caused by a lack of sleep duration or quality. A few things can help minimize sleepiness after drinking coffee:

• Try decaffeinated coffee: Caffeine can be removed from coffee with various methods. Decaffeinated coffee contains only small amounts of caffeine. You can replace all or part of your coffee consumption with decaf to greatly reduce total caffeine intake.
• Don’t drink coffee close to bedtime: Your body removes half of the caffeine you consume in about five hours, although this can vary between individuals. This means you’ll still have 50% of the caffeine in your blood 5 hours after drinking. You can protect your sleep by having coffee earlier in the day.
• Limit other sources of caffeine: Energy drinks, soda, sports drinks, some teas, pre-workouts, and over-the-counter medications contain caffeine. Cutting down on some of these other caffeine sources may help improve your sleep and prevent post-caffeine crashes.
• Stay hydrated: High doses of caffeine can have diuretic effects—increasing urination. If you’re not drinking enough water, coffee can add to dehydration. You can remind yourself to drink enough water throughout the day.
• Change your coffee habits: When you drink the same amount of coffee every day, your body gets used to it, and it doesn’t make you feel as awake. People often drink more coffee to get the same boost, but this creates a cycle of increased consumption with less effect, building caffeine tolerance. Changing your coffee habits periodically can help reset your system.

Coffee contains caffeine, which promotes wakefulness. However, you may still feel sleepy after the caffeine starts to wear off, especially if you haven’t had enough sleep. Regularly drinking coffee can also diminish its waking effects, leading to higher consumption and reduced effects over time.

You can reduce the caffeine crash by getting enough sleep and occasionally changing your coffee habits.