Almost everyone loves a good cup of coffee in the morning. Four out of five adults consume caffeine daily. But caffeine isn’t just used to wake you up and start your day. Plenty of athletes (and your average Joe) swear by pre-workout supplements that contain a lot of caffeine. But what does caffeine even do to your body? Is it actually enhancing your performance, or can it do more harm than good? The answer isn’t as simple as you might think.

Caffeine is a stimulant. It works by blocking the chemical adenosine, which is responsible for making you feel tired. When consumed in moderate amounts, caffeine intake can make you feel more alert, energetic, and focused. It can improve memory temporarily when consumed before a task that requires recall and concentration. The effects of caffeine peak in about an hour after consumption and last for about 4-6 hours, waning as time passes. Generally, for a healthy adult, you want to consume less than 400 mg of caffeine a day to avoid unwanted side effects and potential health problems. 

Because caffeine affects your nervous system, it can also affect your sleep cycle and cause anxiety when consumed too late in the day or too high amounts. If you can’t sleep, reconsider your caffeine intake. Caffeine decreases melatonin production, which your body needs to fall asleep. Limiting your late afternoon and evening intake can help reduce this effect. Caffeine can also increase anxiety and cause you to feel jittery. This is why, if you have a panic disorder or are prone to anxiety, you may be advised not to drink caffeine.

On the other hand, caffeine can temporarily enhance your mental well-being by increasing the amount of dopamine your brain releases. In moderate amounts, this seems to help people feel happier and decrease symptoms of depression. This effect is temporary, however, and it is worth noting that the more dopamine your brain gets used to, the more you’ll require in the future to get the same effects. This is, in part, what leads us to caffeine withdrawal. When consumed for long periods of time, you become addicted to caffeine, and cutting it down or out entirely can cause you to feel more depressed and tired than before you even took your first sip. Part of the reason you experience caffeine withdrawal is the lack of dopamine that your brain is producing. Low dopamine levels can make you feel tired, moody, and unmotivated, among other symptoms. However, your brain usually rebalances within a few days. 

So we know what it does to the brain, but what does it do to the rest of your body? Unlike most substances and supplements, caffeine can affect cells in multiple parts of your body at once, not just your brain. This includes muscle cells. Your heart is, of course, a muscle. High levels of caffeine intake can increase your risk of heart problems, especially if you have a preexisting condition. Consuming in moderate amounts does not seem to cause heart problems. As a diuretic, caffeine also makes you have to pee more frequently.

But what specifically makes caffeine so popular amongst athletes and beginners alike? As previously discussed, caffeine makes you less tired and more focused, which are great things if you are about to start a workout. Although researchers are unsure why, caffeine may improve muscle performance by activating the central nervous system. Caffeine can enhance your ability to perform endurance exercises, such as cycling and running. This is particularly true in athletes and has diminishing results in beginners. One large review of studies found that caffeine slightly improved endurance when used in moderate doses of 1.4–2.7 mg per pound (3–6 mg per kg) of body weight. Another study found moderate benefits for cyclists in terms of speed and endurance. Some sports organizations have begun to ban its use in athletes. The positive effects of endurance training were much less prominent in non-athletes. 

The effects of caffeine on power-based workouts (like strength training) are less well-researched, but there seem to be some positive effects. Several studies have compared strength training performance with a placebo vs. caffeine. One study found that 12 people who performed bench presses after consuming 1.4 mg of caffeine per pound of body weight had significantly increased power output vs the placebo. However, 12 people is a very low sample size, and these results should be studied further. In a different study, also with 12 people, compared to the placebo, individuals who consumed 1.4 or 2.7 mg per pound of body weight increased their mean power output by performing 5 sets on a bench press throw. In general, since less is known about the effects of performance that caffeine provides for power-based exercises, it’s hard to say if caffeine offers much to the layman during weight-lifting sessions. But if it helps you get going and get out of the house, that’s worth it in my book. Just don’t overdo it!