What to Know About How Long Caffeine Lasts

Medically Reviewed by Christine Mikstas, RD, LD on July 12, 2023
3 min read

Caffeine is a common feature of many sodas, coffee, and food products. It’s a drug that is made 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?

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 provides.

Before caffeine is processed in drinks and foods, it has a very bitter taste. It may enhance the flavors of some foods and drinks like coffee and chocolate, but most sodas and teas are designed to eliminate 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 to 300 milligrams (mg) of caffeine per day. Here’s how much caffeine is in your average food and drinks:

  • Espresso: 127 mg per 2 fluid ounces
  • Energy drink: varies between 70-240 mg caffeine in a 16-fluid ounce drink
  • Instant coffee: 62 mg caffeine in 8-fluid ounce serving
  • Black tea: 48 mg caffeine in 1 cup (8 fluid ounces)
  • Soda: 34 mg caffeine in 12 fluid ounce can
  • Milk chocolate: 8.8 mg caffeine in a 1.55 ounce bar (44 grams)

Effects of caffeine. 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 

It is possible to overdose on caffeine if you have too much. 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
  • Faster breathing 
  • Feeling nervous or anxious
  • Irritability and agitation
  • Fast heart rate
  • Confusion
  • Panic attack‌
  • Seizures

Long-term effects. If you get a lot of caffeine over a long period of time, 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 

You notice the effects of caffeine within 15 minutes. The levels in your bloodstream peak an hour later and remain there for several hours. About 6 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 urinate more often
  • Higher body temperature
  • Faster breathing
  • Headache
  • Lack of concentration‌
  • Stomach pain

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.

Withdrawal. It can be hard to cut caffeine out of your diet. Withdrawal symptoms begin 12 to 24 hours after you last had any and can linger for up to 7 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 affect your bone density by taking away calcium from your bones. This leads to a faster progression of osteoporosis.

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:

  • Choline
  • Ginseng
  • Glucuronolactone
  • Guarana
  • Inosol
  • Kola nut
  • Malic acid
  • Maltodextrin
  • Niacin
  • Pantothenic acid
  • Taurine
  • Theanine
  • Tyrosine
  • Yerba mate