Caffeine Makes Me Tired, So I Asked a Sleep Expert to Explain Why

I know, I know—caffeine is a stimulant. By definition it shouldn’t make a person tired. But I swear, sometimes a mid-day cold brew actually makes me feel more ready for a nap than anything else—forget about feeling wired. What gives? Is it my imagination that caffeine makes me tired? Perhaps there's more to the story. To answer my question, I relied on some experts.

Meet the Experts

• Vanessa Rissetto, MS, RD, CDN and co-founder of Culina Health
• Michelle Worley, registered nurse and Director of Clinical Operations at Aeroflow Healthcare who also oversees their sleep treatments
• Carlyn Rosenblum, MS, RD at MTHR Nutrition

So, am I crazy for thinking caffeine makes me sleepy?

“Not crazy at all,” Rissetto assured me. Worley agreed, “The most well-known effect caffeine has on the brain is alertness, but that isn’t the only one.” So, can caffeine actually make people feel tired? Let’s take a look.

1. You’re Drinking Too Much of It

How many cups of coffee, cans of Red Bull or pots of tea are you having a day? More than three? That might explain why you’re getting tired; it’s a lot of caffeine. Says Rissetto: “If you're drinking caffeine in excess of three cups or more a day, it can make you go to the bathroom more, causing dehydration which can make you feel dizzy and sleepy.”

2. Excess Caffeine Blocks Adenosine Receptors

When caffeine hits our brain, Worley explains, it adheres to your brain’s adenosine receptors. Adenosine is what helps us feel sleepy. So, when caffeine binds to those adenosine receptors, it stops our brain from feeling tired. But—there’s a twist! “Just because our brain is no longer processing the adenosine doesn’t mean it stops producing it. When the caffeine inevitably wears off, you’re left with an adenosine buildup which makes you feel even more tired.”

3. The Sugar You Add Is the Real Culprit

There are two types of people in this world: People who take some sugar in their coffee and people who take some coffee with their sugar. If you fall into the latter camp, you might be feeling exhausted after drinking your morning joe because of what you’re putting in it. “If you load your coffee up with sugar and sweeteners, when that wears off you can get a sugar crash and again feel pretty tired and sluggish,” Rissetto reminds us. This also applies to super sweet creamers and energy drinks with long lists of other ingredients.

4. It Could Be Mold

Ew. We know. However, studies show that caffeine contains mold called mycotoxins, which according to the World Health Organization are “are toxic compounds that are naturally produced by certain types of moulds (fungi). Moulds that can produce mycotoxins grow on numerous foodstuffs such as cereals, dried fruits, nuts and spices.” Eek. Mycotoxins have been linked to causing chronic fatigue. To avoid this mold, try to diversify the coffee you drink, whether that's changing up coffee shops or buying different brands. And keep an eye out for coffee beans that look discolored or shriveled.

5. You’ve Developed a Caffeine Tolerance

Drinking lots of coffee on the regular? Chances are, you’ve developed a mild tolerance to the effects of caffeine, Worley explains. So that lightening jolt of energy you used to get after your first espresso doesn’t hit the same now that you take two shots a day. “Weaning yourself off of caffeine and then reintroducing it later may help,” says Worley.

6. Your Body Reacts Differently to Caffeine

Per Rissetto: “Some people can be more sensitive to caffeine than others. They may feel as if they've had five or six cups of espresso after drinking only a few sips of regular coffee. People with this sensitivity metabolize caffeine more slowly, and their symptoms may last for several hours.” You may even metabolize caffeine in a dramatically different way based on your genes, says Worley. “Everyone’s body interacts with caffeine differently based on a variety of factors. For example, those with anxiety disorders may experience heightened negative symptoms when consuming caffeine, while for others, a few sips of coffee may feel more like several cups of coffee. Symptoms of sensitivity to caffeine include a racing pulse, headaches, jitters and even insomnia,” Worley breaks down.

7. You’re Experiencing Caffeine Withdrawal

If someone consumes enough caffeine over certain a period of time, their body can become dependent on it, says Worley. “If that happens and someone tries to suddenly and completely remove caffeine from their diet—what many call ‘going cold turkey’—they can experience a variety of symptoms ranging from headaches to fatigue to depression.” So, in this case, it’s the absence of caffeine that might be making you sleepy. If you’re trying to quit coffee and want to avoid the withdrawal symptoms, try the gradual approach: “Cut back on your consumption by ¼ of a cup every two to three days, or switch to green tea for less caffeine. Continue cutting back until you’re no longer consuming caffeine,” says Rissetto.

8. Caffeine Is a Diuretic

Remember how we told you that drinking too much caffeine can dehydrate you if you consume too much? Well, here’s a little more on that: Caffeine can dehydrate you even after one cup—it all depends on your body (remember #6?). “Caffeinated drinks like tea and coffee act as diuretics, causing people to void their bladders more frequently and causing dehydration. That dehydration combined with caffeine withdrawal and the adenosine buildup can make someone feel exhausted,” says Worley.

9. You're Drinking It at the Wrong Time of Day

Are you sipping that cup of coffee first thing in the morning on an empty stomach? According to Rosenblum, this can increase cortisol—already high in the morning—which can affect how your body regulates energy and alertness. In other words: It can throw your sleep cycle off, making you feel groggy at hours you should have a pep in your step. Instead, try waiting for that first cup until after breakfast, somewhere between 9:30 a.m. and noon.

If you’re trying to understand the effects caffeine has on you, it’s important to know how long the chemical can stay in your system: “Caffeine can start stimulating the body in as little as 15 minutes after it’s consumed, and it can stay in your system for another three or four hours after that,” says Worley. That means, for most healthy adults, it’s safe to consume up to 400 milligrams of caffeine per day, or about four cups of coffee.

Here’s the thing: Rissetto and Worley both agree that in moderation, you can make caffeine work for your body to help fight fatigue. “Watching the amount of caffeine you consume on a daily basis is a good start,” says Rissetto. Match that with regular exercise and water consumption.

“Some ways to stay awake without the ‘crash,’” guides Worley is to “switch from regular coffee to decaf or tea, gradually cutting back on caffeine to reduce feelings of withdrawal.” And, of course, make sure you get enough sleep in the first place. Like we mentioned above, consider swapping regular sugar with monk fruit sweetener or drinking it sans anything at all!

Says Worley: “Since many people consume caffeine for the jolt of energy it provides, which is made possible by blocking the brain’s sleep-inducing chemicals, it should come as no surprise that it can make it more difficult for people to sleep. For the best possible chance at a good night’s sleep, caffeine drinkers should stop consuming caffeine at least seven hours before they plan to go to sleep.” Yup, you might want to rethink that elegant post-dinner espresso shot.

The most important thing to note is that caffeine—despite how easily we can get our hands on it—has a powerful effect on our body. It can stimulate us to feel awake. And if we drink too much of it—and are especially sensitive, tolerant or withdrawing from it—coffee can have adverse effects, making us feel depleted. So be mindful of your intake. Keep track of your what kind of caffeine you’re drinking and go from there. Are you drinking three big cans of Monster energy drinks at midnight? Are you saturating your morning cup of tea with sugar? There are lots of variations. Study your habits, take notes and work from there.