Caffeine is a central nervous system stimulant. It can temporarily make you feel more awake and energetic, but it can also give you the jitters. Withdrawal or overdose can cause a range of problems.
Caffeine on the Brain
Not a Hangover Cure
Nausea and Vomiting
Increased Blood Pressure
Caffeine in the Bones
Bloodstream to Baby
Fertility Woes
The Jitters
Increased Urination
Rapid Heartbeat
Muscle Aches
Painful Breast Lumps

Effects of Caffeine on the Body

Caffeine is a naturally occurring substance found in many plants, including coffee beans and tea leaves. Kola nuts and cacao pods also contain caffeine. Caffeine can also be man-made, and it is added to many of our foods and drinks. Many over-the-counter and prescription medications contain caffeine. According to the U.S. Food and Drug Administration(FDA), about 90 percent of the world’s population ingests some form of caffeine. In the United States, about 80 percent of us take in some caffeine every day.
According to the Mayo Clinic, it’s safe for most healthy adults to consume up to 400 milligrams of caffeine per day. How much caffeine each beverage contains varies a lot, so reading labels is important. There’s also a great variation in the amount of caffeine an individual can tolerate without unpleasant side effects. If you consume roughly the same amount of caffeine every day, you can develop a tolerance to it. Your tolerance level is affected by your age, body mass, and any health conditions you may have. Caffeine can also interact with certain medications.
Six hundred milligrams a day is generally considered too much, according to the FDA. That’s the equivalent of four to seven cups of coffee. Keep in mind that a standard size cup of coffee is eight ounces. If you’re using a mug or getting your fix at a coffee house, chances are you’re drinking 16 ounces or more. If you usually take in a lot of caffeine, stopping suddenly can cause symptoms of withdrawal. It’s best to decrease your consumption slowly.
Caffeine provides no nutritional value. It’s tasteless, so you don’t necessarily know if it’s in your food. However, it can affect your mood and cause physical side effects.

Central Nervous System

Caffeine reaches your brain quickly and acts as a central nervous system stimulant. The most noticeable effect is alertness. It can help you feel more awake and less tired, so it’s a common ingredient in medications to treat drowsiness.
Caffeine and headaches have a complicated relationship. Too much caffeine can give you a headache. However, your body develops a tolerance to caffeine. If you normally consume caffeine and stop suddenly, it can cause a headache. Caffeine is used in some over-the-counter and prescription-strength headache and migraine remedies.
Despite the common wisdom of drinking coffee to recover from too much alcohol, caffeine doesn’t actually help your body process alcohol any faster.
If you’re not used to it, caffeine can give you the jitters. If you have an anxiety disorder or sleep disorder, caffeine may make it worse.
Symptoms of caffeine withdrawal include anxiety, irritability, and drowsiness. In some people, sudden withdrawal may cause tremors.
It’s also possible to overdose on caffeine. Symptoms of an overdose include confusion and hallucinations. An overdose can result in death due to convulsions.

Digestive and Excretory Systems

Caffeine raises the amount of acid in your stomach and may cause heartburn or upset stomach. It’s also a diuretic, triggering your body to get rid of water. That’s why it’s not a great thirst quencher. Extra caffeine doesn’t get stored in your body. It is processed in the liver and exits in your urine.
If you have stomach problems, like acid reflux or ulcers, ask your doctor if it’s okay to have caffeine. Large doses of caffeine cause you to lose too much water, especially when consumed in conjunction with exercise.
Withdrawal from caffeine can cause nausea and vomiting. Symptoms of caffeine overdose include diarrhea, excessive thirst, and increased urination.

Circulatory and Respiratory Systems

Caffeine is absorbed from your stomach. It reaches its highest levels in your bloodstream within an hour or two.
Caffeine can make your blood pressure go up for a short time. In most people, there is no long-term effect on blood pressure. If you have irregular heart rhythms, caffeine may make your heart work harder. If you have high blood pressure (hypertension) or heart-related problems, ask your doctor if caffeine is safe for you.
An overdose of caffeine may cause rapid or irregular heartbeat and breathing trouble. In rare cases, caffeine overdose can cause death due to convulsions or irregular heartbeat.

Skeletal and Muscular Systems

Caffeine in large amounts may interfere with absorption and metabolism of calcium. This can contribute to bone thinning (osteoporosis).
Symptoms of caffeine withdrawal include achy muscles. An overdose can cause muscle twitches.

Reproductive System

Caffeine travels within the bloodstream and crosses into the placenta. Since it is a stimulant, it can cause your baby’s heart rate and metabolism to increase. Too much caffeine can also cause slowed fetal growth and increase risk of miscarriage. In most cases, a little caffeine is safe during pregnancy.
Caffeine can also contribute to painful lumps in the breast (fibrocystic disease). According to the Mayo Clinic, there is some evidence that large amounts of caffeine can interfere with estrogen production and metabolism, making it harder to get pregnant.
If you have lumpy breasts, are pregnant, or are trying to get pregnant, ask your doctor about safe levels of caffeine.