The Side Effects of Too Much Caffeine

The stimulant can have benefits, but there are downsides


Verywell / Alexandra Shytsman

Caffeine, most commonly consumed in the form of coffee, tea, sodas, and energy drinks, improves cognitive function, boosts athletic ability, and can even help turn around a bad mood. Indeed, many believe they can't function without their first cup (or two) of coffee in the morning.

Caffeine offers several benefits but can also cause negative side effects depending on the dose. Learn how much caffeine is too much so you can decide when it's time to pass on that next refill.

Benefits of Caffeine

The taste and aroma of a good cup of Joe is a morning ritual for many. The caffeine in coffee may be merely an added bonus. Others drink coffee or caffeinated beverages precisely for the jolt of energy from caffeine.

Caffeine is a stimulant, and some studies show that small doses of caffeine can improve mental response time and exercise performance. Caffeine can be used to enhance a variety of mental and physical tasks, heightening productivity, concentration, and accuracy—to a point.

Coffee and tea are the most common sources of caffeine in the American diet. Consumption of these drinks is associated with a host of health benefits, including the prevention of certain cancers, diabetes, and heart disease.

However, it can be difficult to discern whether these positive effects are caused by caffeine alone or are the result of a combination of antioxidants present in coffee and tea.

Caffeine is also commonly added to over-the-counter pain relievers like Excedrin (aspirin/acetaminophen/caffeine) where it has been shown to increase effectiveness by 40%. Asthma treatments, ADHD medications, and weight-loss drugs also often include caffeine to enhance their effects.

Side Effects

Most adults don't experience the effects of caffeine intoxication when drinking less than 250 milligrams of caffeine (about 2.5 cups of coffee) per day. You are more likely to experience negative side effects if you exceed the recommended amount of 400 milligrams per day.

The stimulant properties of caffeine increase your blood pressure and heart rate. Consuming too much may give you the "caffeine jitters," which is that jumpy and slightly alarmed feeling. Larger amounts of caffeine may make you irritable, sleepless, and may even trigger anxiety and cause diarrhea.

Other side effects include:

  • Anxiety and nervousness
  • Frequent urination
  • Headaches
  • Heart palpitations or fast heartbeat
  • Incontinence
  • Muscle spasms
  • Upset stomach

Caffeine can act as a diuretic, so it was once assumed that drinking too much coffee or other caffeinated beverages would cause dehydration. However, researchers found that your body adjusts to your caffeine intake, so drinking caffeinated beverages won't increase your need for water.

Beware of caffeine pills and powders that promise to deliver a jolt quickly and effectively—they do exactly that. These products can deliver large doses of caffeine in a very short amount of time.

People with underlying medical conditions should be particularly concerned as they could be more susceptible to the negative effects, such as heart palpitations.

Caffeine Addiction

In addition to the negative short-term effects of too much caffeine, regular caffeine consumption may cause you to develop a dependency. Technically, caffeine does not cause "addiction" in the traditional sense, but you may begin crave the rise in dopamine that's associated with caffeine consumption.

While too much caffeine may be harmful, it's unlikely to cause the negative consequences of a true drug addiction.

Safe Caffeine Consumption

If you have been wondering whether to curb your caffeine intake, first think about whether you have a sensitivity to it.

If you feel jittery, anxious, or have trouble sleeping, it might be a good idea to cut back.

Also, think about your medical conditions, including heart problems or nervous disorders, and any medications you take. Caffeine can affect absorption and interact with certain medications. Speak to your doctor or pharmacist to figure out if you need to take your caffeine intake into account.

Healthy Adults

Most experts recommend no more than 400 milligrams of caffeine per day for most adults. That equates to about four 8-ounce cups (not giant mugs) of brewed coffee; five shots of espresso; or two energy drinks.

Pregnancy and Breastfeeding

Breastfeeding or pregnant women may want to decrease their caffeine intake even more. Consuming more than 200 milligrams of caffeine per day (about 12 ounces of coffee) has been associated with:

  • Poor fetal growth
  • Reduced milk supply for breastfeeding
  • Slightly increased risk of miscarriage

However, study results are mixed, making it difficult to determine a clear link between caffeine intake and poor pregnancy outcomes.


Children are advised to limit or avoid common sources of caffeine (like soda and chocolate). Since caffeine affects the central nervous system as a stimulant and children's brains are more sensitive to caffeine than adults, it may cause the following:

  • Anxiety
  • Hyperactivity
  • Poor sleep patterns
  • Unhealthy growth patterns

Caffeine Overdose

The unpleasant side effects of too much caffeine will usually resolve on their own with time. If you notice an irregular heartbeat accompanied by feeling dizzy or faint, it may be time to call your doctor or go to the emergency room.

Irregular heartbeats can cause a heart attack, especially for someone with a pre-existing heart condition. Seizure disorders can also be triggered by caffeine.

After too much caffeine, most people will feel better within four to six hours. While you wait:

  • Avoid additional sources of caffeine, including chocolate.
  • Drink lots of water and replace your electrolytes, especially if you've been having diarrhea or stomach issues.
  • Try deep breathing, or go for walk to burn excess energy and lower anxiety levels from caffeine.

Reducing Your Caffeine Intake

Kicking the caffeine habit cold turkey isn't recommended as it can lead to symptoms of caffeine withdrawal, including:

  • Headaches
  • Irritability
  • Muscle aches

Withdrawal symptoms will pass with time. Blending regular caffeinated beverages with decaf versions can help ease symptoms as you reduce your caffeine dependency.

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