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Written by WebMD Editorial ContributorMedically Reviewed by Shruthi N, MD on January 28, 2026

• What Is Caffeine?
• What Are the Effects of Caffeine on the Body?
• Can You Overdose on Caffeine?
• How Long Does Caffeine Last?
• What Are the Pros of Caffeine?
• What Are the Cons of Caffeine?
• Other Considerations
• Takeaways

4 min read

Caffeine is a common feature of many sodas, coffee, and food products. It’s found naturally in the leaves and seeds of many plants and gives an energy boost when consumed. But how long do the effects of caffeine last, and how does it affect your health?

What Is Caffeine?

Caffeine is classified as a drug because it stimulates the central nervous system, raising alertness. Caffeine is popular because of the temporary energy and mood boost it offers.

Before caffeine is processed in drinks and foods, it has a very bitter taste. It may improve the flavors of some foods and drinks, such as coffee and chocolate, but most sodas and teas are designed to remove the bitter taste of caffeine.

Caffeine is addictive, and that’s one reason it’s used in so many products — to keep you coming back for more. If you drink coffee or soda regularly and then stop, you may have withdrawal symptoms.

Medical professionals consider moderate consumption to be 200-300 milligrams (mg) of caffeine per day. Here’s how much caffeine is in your average food and drinks:

• Espresso: 127 mg caffeine per 2 fluid ounces
• Energy drink: 70-240 mg caffeine per 16 fluid ounces
• Instant coffee: 62 mg caffeine in 8 fluid ounces
• Black tea: 48 mg caffeine in one cup (8 fluid ounces)
• Soda: 34 mg caffeine in a 12-fluid-ounce can
• Milk chocolate: 8.8 mg caffeine in a 1.55-ounce bar (44 grams)

What Are the Effects of Caffeine on the Body?

Caffeine may give you a temporary mood and energy boost, but its addictive properties can be dangerous. How caffeine affects you depends on:

• Your weight, height, and health
• Whether you get caffeine regularly
• Other drugs that are taken at the same time ‌
• Amount of caffeine consumed 

If you get a lot of caffeine over a long period, you may develop chronic side effects. Talk to your doctor if you have:

• Anxiety
• Trouble sleeping
• Ulcers
• Osteoporosis 
• Irritability and headaches
• Dizziness 
• Ears ringing
• Uncontrollable shaking
• Weakness and tiredness
• Rapid or irregular heartbeat
• Fast breathing
• Lack of appetite
• Nausea, vomiting, and diarrhea
• Sudden thirst
• Low blood pressure
• Seizures‌
• Confusion 

Can You Overdose on Caffeine?

It is possible to overdose on caffeine if you have too much of it. Caffeine in beverages and food is usually safe, but taking it in powder form can be dangerous. Get medical attention right away if you have any of these symptoms:

• Uncontrollable shaking
• Nausea or vomiting
• Severe belly pain
• Diarrhea
• Rapid breathing
• Feeling nervous or anxious
• Irritability and agitation
• Fast heart rate
• Confusion
• Panic attack‌
• Seizures

What are the symptoms of too much caffeine?

Think about cutting back on your caffeine habit if you notice symptoms such as:

• Headaches
• Being unable to sleep (insomnia)
• Feeling nervous or cranky
• Peeing often or not being able to control when you pee
• Shaky muscles
• Upset stomach

How Long Does Caffeine Last?

You may notice the effects of caffeine within 15 minutes. The levels in your bloodstream peak an hour later and remain there for several hours. About six hours after you consume caffeine, half of it is still in your body. Caffeine may not completely clear your bloodstream until after 10 hours.

Short-term side effects include:

• Feeling alert
• Desire to be active
• Restlessness or excitability
• Anxiety and irritability
• Dehydration
• Need to pee more often
• Higher body temperature
• Faster breathing
• Headache
• Lack of concentration‌
• Stomach pain

What Are the Pros of Caffeine?

Increased energy. Most people drink caffeine to beat feelings of sluggishness. It gives a burst of energy that can last hours.

Better mood. Caffeine often gives you a boost that enhances your mood. It may make you feel happier and lighter.

What Are the Cons of Caffeine?

Withdrawal. It can be hard to cut caffeine out of your diet. Withdrawal symptoms begin 12-24 hours after you last had any and can linger for up to seven days. These symptoms can include:

• Severe headache
• Extreme fatigue
• Nausea and vomiting 
• Anxiety and irritability
• Sweating
• Feeling depressed 
• Inability to concentrate 
• Muscle pain or weakness

Bone density loss. For women who’ve gone through menopause, caffeine can take away calcium from their bones, affecting their bone density. This speeds up the worsening of osteoporosis.

Other Considerations

Caffeine has some desirable side effects, but many people avoid it for health reasons. You may know the obvious sources of caffeine, but it can also hide in food and medication additives.

If you’re concerned that a medication may contain caffeine, talk to your doctor. They may be able to recommend something without it.

Be sure to check packages for these ingredients that contain caffeine:

• Black tea
• Cacao 
• Cocoa
• Guarana
• Green tea
• Kola nut
• Kombucha
• Matcha
• Mocha flavoring
• White tea
• Yaupon
• Yerba mate

How can I flush caffeine out faster?

Unfortunately, you can’t. But you can follow these tips to offset the effects of caffeine in your system: Drink plenty of water, move more (for example, take a walk), and try to relax with methods like meditation, deep breathing, or yoga.

Takeaways

Caffeine is an ingredient in many sodas, coffee, and food products. It makes you more alert by stimulating your central nervous system. It may take more than 10 hours to completely clear caffeine from your bloodstream. Having too much caffeine can lead to side effects such as anxiety, ulcers, and trouble sleeping. If you have caffeine often and notice side effects like these, slowly cut back to avoid symptoms of withdrawal.

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