Why Coffee Makes You Sleepy

Caffeine is a stimulant that increases alertness and boosts energy levels. Caffeine itself doesn’t cause drowsiness. Coffee, however, is a complex beverage, and drinking it can make you feel tired at times. Here’s a look at why coffee can actually make you sleepy and fatigued, even though it’s caffeinated.

Adenosine Will Make You Sleepy When the Caffeine Wears Off

The caffeine in coffee blocks adenosine receptors in your brain from receiving adenosine, which is a neurotransmitter that causes fatigue. Although caffeine prevents your brain from receiving adenosine, it doesn’t stop your body from producing the neurotransmitter. Thus, when the caffeine wears off, there is a buildup of adenosine that will make you sleepy.
Caffeine isn’t making you sleepy, because it doesn’t impact how much adenosine your body manufacturers. It does, however, delay the effects of that adenosine so that you feel it all at once in a rush when the caffeine wears off.

Sweet Coffee Will Give You a Sugar Crash

If your coffee’s especially sweet, you may experience a sugar crash shortly after drinking it. Sugar is processed much more quickly than coffee, and it leaves you without energy after it’s used up by your body. If you drink coffee-flavored drinks that have lots of sugar but little coffee, you may actually be experiencing a sugar rush and crash, more than a caffeine boost.

Coffee Makes You Dehydrated

The primary reason why coffee makes you sleepy sometimes is likely because it’s making you dehydrated.
Coffee is a diuretic. In other words, it makes you need to urinate. Drinking it to stay awake can quickly lead to a vicious dehydrating cycle that actually makes you more tired. The cycle goes like this:

1. You drink a cup of coffee and soon afterwards need to use the bathroom.
2. When you go to the bathroom, your body loses water.
3. When your body loses water, your blood thickens.
4. When your blood thickens, it moves more slowly through your arteries and veins.
5. As your blood slows down, it delivers less oxygen to your body.
6. Without as much oxygen, you become sluggish.
7. You may reach for more coffee to combat the sluggishness, thus starting the cycle again.

Because you’re drinking coffee, you likely aren’t drinking water to rehydrate yourself. At least, you probably aren’t drinking as much as you should be.
Additionally, coffee is a vasoconstrictor, which further compounds the problem. Coffee makes your arteries and veins get narrower. As they narrow, it only becomes more difficult for your thickening blood to flow through them.

You Can Limit the Effects of Coffee

If coffee regularly makes you sleepy, there are a few things you can do to limit its fatiguing effects:

• Moderate your coffee intake. (The Mayo Clinic recommends having no more than 400 milligrams of caffeine a day, which is about 2 to 4 cups of coffee.)
• Avoid coffee beverages with lots of sugar.
• Drink plenty of water with your coffee.