5 Reasons Coffee Can Make You Sleepy
By Michelle Zhang, Wellness Writer 
Shawna Robins: Nutritionist
Shawna Robins is a #1 Amazon bestselling author, graduate of the Institute of Integrative Nutrition (IIN), a national board-certified health and wellness coach, and the visionary creator of Kaia Health and Wellne...Read more
Key Takeaways
- Caffeine Blocks Adenosine: Caffeine in coffee interferes with adenosine, a chemical in the brain that regulates sleep. It prevents adenosine from binding to receptors responsible for promoting relaxation and sleepiness. When the caffeine wears off, adenosine levels can surge, leading to extreme fatigue and drowsiness.
- Coffee Can Act as a Diuretic: Consuming excessive amounts of coffee, especially more than four cups a day, can have a diuretic effect. This means it increases urination and may lead to dehydration. Dehydration can cause daytime sleepiness, lethargy, and even anxiety. It’s important to stay hydrated by drinking water alongside your coffee consumption.
- Coffee Sweeteners and Blood Sugar Levels: Coffee additives like sugar, creamers, and syrups can contain high levels of sugar. This can lead to a sugar crash, where blood glucose levels drop rapidly after an initial spike, causing sleepiness, mood swings, and dizziness. Reducing sugar in your coffee and being mindful of sugary coffee drinks can help prevent these crashes.
For many people, a warm, rich cup of coffee is the perfect way to get the day started. In fact, it is the most popular caffeinated beverage in the United States. The caffeine in coffee, about 80 to 100 milligrams per cup, stimulates the nervous system, and provides an energy boost.
However, we all react to caffeine differently. One person may drink several cups of coffee and experience minimal effects. In contrast, another person could drink one cup and experience strong, even negative side effects, such as an elevated heart rate, digestion problems, and a jittery feeling. Coffee can also cause the opposite effect—instead of causing wakefulness, it can cause some people to become sleepy and unfocused.
If you experience drowsiness after drinking coffee, it may be due to one of the reasons outlined below.
1. Caffeine Blocks Adenosine
Adenosine is a naturally occurring compound that plays a crucial role in various biochemical processes in the body, particularly in energy transfer and the regulation of sleep.
“It’s a neurotransmitter that is synthesized in the liver and travels through the blood,” says Shawna Robins. “It can act as a central nervous system depressant, which makes you sleepy.”
In the brain, adenosine acts as a neuromodulator and is involved in the regulation of blood flow, the sleep-wake cycle and regulating our sleep schedule, and the suppression of arousal and wakefulness. Adenosine also has functions in the regulation of the immune system and the modulation of inflammation.
Much like melatonin, the sleep hormone, adenosine levels increase during the day to keep us awake. At night, they decrease to help us fall asleep. Adenosine does this by binding to special receptors in the brain that slow activity and cause relaxation. When you drink coffee, caffeine binds to these receptors and prevents them from receiving adenosine.
However, the body still produces adenosine in the morning even if the receptors are not absorbing it. This causes a build-up of the chemical in the body. Once caffeine is metabolized, the high levels of adenosine can cause extreme fatigue. Since caffeine absorbs quickly, some people may feel these adverse effects 45 minutes after consumption.
2. Coffee is a Diuretic
For those who drink more than four cups of coffee per day, caffeine can act as a diuretic. This means it passes through your body quickly, causing you to use the bathroom more frequently. Over time, water loss can affect your heart’s ability to maintain blood pressure and put you at risk of dehydration.
If you do become dehydrated, you may experience daytime sleepiness and lethargy. Dehydration can also lead to rapid heart rate and low blood pressure, which often triggers anxiety. In most cases, drinking a moderate amount of coffee, one to two cups a day, will not cause dehydration. Therefore, be sure to monitor your coffee intake and overall caffeine intake each and every day.
Although caffeinated beverages, such as coffee, energy drinks, and soft drinks, may force us to use the restroom more often, the water in coffee can counteract dehydration.
However, if you drink a lot of coffee, be sure to drink plenty of water throughout the day. According to the USDA water intake recommendations, adult men should have around 13 cups per day, and adult women should have 9 cups.
“I use the baseline of water consumption should be ‘one half a person’s body weight in oz,'” Robins suggests as an alternative. “It’s more specific to the individual.”
3. Coffee Sweeteners Affect Blood Glucose Levels
Most coffee creamers have high levels of sugar. Plus, specialty coffee drinks at your local cafe may contain whipped cream, flavored syrup, honey, and chocolate, all of which contain refined sugars that cause what many people describe as a “sugar crash” once metabolized.
A sugar crash happens when you consume too much sugar at once and the body produces insulin to offset it, causing a drastic drop in blood glucose (blood sugar). Blood sugar fuels the body and increases energy, which is one reason people prefer to drink coffee before a workout. This drop in blood sugar levels causes a sleepy, sluggish feeling. A sugar crash can also cause anxiety, mood swings, dizziness, and hunger.
To prevent these effects, try to limit the amount of sugar you add to your coffee and the number of sugary drinks you consume each day. If you develop a sugar crash, you can counteract these effects with a healthy snack, such as nuts, seeds, hard-boiled eggs, or yogurt.
4. Tolerance to Caffeine
Over time, avid coffee drinkers may build-up caffeine tolerance. Caffeine prevents adenosine from binding with receptors. However, to combat this, the body may begin to produce more adenosine receptors. One study found that physically active adults began to experience fewer caffeine effects after 15 days of regular consumption.
However, research on caffeine tolerance is still inconclusive, as other studies suggest regular consumption does not change the rate of absorption or metabolism.
5. Coffee Beans Many Contain Mold
A recent study found that several coffee samples were contained with mycotoxins, such as aflatoxin B1 and ochratoxin A. Although these amounts are below the legal limit and deemed safe for human consumption, other studies have found that mycotoxins can lead to chronic fatigue syndrome. For those who regularly drink coffee, stopping abruptly can lead to a caffeine withdrawal, which can lead to several uncomfortable side effects, including sleepiness, headaches, nausea, and irritability. A gradual decrease in caffeine consumption is a safer alternative. If you want to stop drinking coffee, try decreasing the amount you consume by ¼ cup every two to three days. Eventually, you will decrease your consumption completely and have fewer side effects than if you stopped all at once. Caffeine can raise blood levels and elevate the heart rate. However, research shows these effects are temporary and are not detrimental to your heart health or cholesterol levels. Those with heart disease and high blood pressure may want to discuss caffeine consumption with their doctor, since high doses of caffeine may be dangerous for these individuals. Since caffeine is a stimulant, it can cause adverse effects for those with anxiety. Caffeine heightens the “fight or flight” response, a physiological reaction to a perceived threat or danger. For those with anxiety, even minor things can trigger this response. The consumption of caffeine can make this reaction even more dangerous and trigger an anxiety attack. The body begins to absorb caffeine immediately. Since it passes through the tissue lining the mouth, throat, and stomach so quickly, most individuals feel the effects of coffee fairly quickly, in about 15 to 20 mins. Studies show that some individuals may feel the effects of coffee up to 8 hours after consumption. This means your afternoon coffee could cause you to feel active and alert well past your bedtime. Therefore, it is best to avoid caffeinated beverages and other items with caffeine after 2 p.m. This includes energy drinks, soda (including diet soda), PMS medicine, headache medicine, chocolate, matcha, green and black tea. This stretch of time allows your body to metabolize caffeine and keep it from disrupting your sleep. Research on this is somewhat mixed. One 2022 study noted that self-medicating ADHD with caffeine can lead to caffeine use disorder symptoms, without mitigating ADHD symptoms for greater well-being. However, a separate 2022 review of caffeine for ADHD in animal studies suggests caffeine could have a supplemental role in ADHD treatment. Robins notes some of her clients drink 4 to 5 cups of coffee across the day to help them with their focus and to improve energy levels.Frequently Asked Questions
What happens to your body when you stop drinking coffee?
Is caffeine bad for your heart?
Can coffee help anxiety?
How long does it take for coffee to take effect?
How many hours before bed should I stop drinking coffee?
Can coffee help with ADHD?
Conclusion
Coffee is a staple in many people’s lives; however, caffeine is a powerful stimulant, and consumption should be monitored. If you find yourself sleepy after drinking coffee or if you begin to experience any adverse effects, such as dizziness and jitteriness, it is best to reduce your intake. Also, if you suffer from a sleep disorder, such as insomnia, restricting coffee consumption to the morning can help you get a better night’s sleep.
This article is for informational purposes and should not replace advice from your doctor or other medical professional.
Michelle Zhang, Wellness Writer
Michelle Zhang is a regular contributor to our Zoma blog and is our go-to sleep researcher. In her time with Zoma, Michelle has researched and published many articles on widespread sleeping habits and troubles. In her time outside of Zoma, Michelle is an occupational therapist and long-distance runner. She believes leading a healthy lifestyle is the key to getting better sleep at night. Michelle's work has been featured on Men's Journal, The Frisky, and The Mighty.
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