The effects of caffeine usually start within 5 to 30 minutes and can last from 8 to 12 hours. Less than 200 mg of caffeine (1 or 2 cups of coffee) can make you more alert, put you in a better mood, and make you feel less tired. It can also improve physical work and your thinking.
Small amounts of caffeine might make your blood pressure to go up, increase your heart rate, and make you pass urine more. If you have caffeine before bed, it can make it harder to fall asleep. You might sleep for a shorter time or not as deep. Older adults may have their sleep affected by caffeine more than younger adults.
Larger amounts of caffeine (600 mg or more) can:
People who have panic attacks shouldn’t use large amounts of caffeine. They might be more sensitive to its effects and it can trigger nervousness and anxiety.
It's rare for adults to die from a caffeine overdose. You would have to inject at least 3.9 g of caffeine or swallow about 10 g. However, children can die from as little as 1 gram of caffeine. Some products with caffeine have higher than the recommended doses of caffeine for children and teens (for example, some energy drinks), so using them may cause health or behaviour problems.
Caffeine can be used to treat some types of headaches, including migraines. Some over-the-counter pain medicine contains caffeine. Your doctor can tell you if caffeine might work for you.
Caffeine doesn’t decrease your appetite so there's no point in using it to diet or decrease your hunger.
Caffeine doesn’t help you sober up if you are drunk. Mixing caffeine and alcohol increases your chances of drinking and driving or getting into a vehicle with someone who has been drinking. This could lead to you or someone being hurt or killed. You might not realize how drunk they are and the caffeine or energy drink might mask the drowsiness related to the drinking. You might also drink more than normal if you combine alcohol and caffeine (energy drinks). The more you alcohol you drink the higher the risk that you may pass out or suffer an alcohol related injury.
Most healthy adults that use low to moderate amounts of caffeine (up to 3 cups of coffee) every day don’t seem to have any long lasting effects. Some women who drink (more than 3 cups a day) may be at risk of bone fractures (especially in the hips) as they get older.
Regular use of more than 600 mg of caffeine might cause the short-term effects listed above. Long-term effects at this level may include chronic insomnia, constant anxiety, depression, and stomach problems. It can also cause high blood pressure or make high blood pressure worse.
More than 300 mg of caffeine (about 2 to 3 cups of coffee) in a day may be linked to miscarriages and low-birth weight babies. Caffeine is passed through breastmilk, which might make your baby irritable or have trouble sleeping. If you're pregnant or breastfeeding you may want to limit or not have any caffeine.
Some products with caffeine, like some energy drinks, have higher than the recommended doses of caffeine for children and teens. Using them for this age group may cause health or behaviour problems.
Caffeine can affect children and teens differently than adults. Because their bodies are smaller, what is a normal amount of caffeine for an adult may have a stronger effect on a child. Children who drink pop or energy drinks with caffeine might feel anxious, be irritable, have trouble sleeping, or wet the bed.
Some teens who use a lot of caffeine may have health problems like an increased or abnormal heart rate or chest pain. If this happens, they may have to go to the hospital or need an ambulance.
College and university students might harm their health by using lots of caffeinated products (such as coffee, energy drinks, caffeine pills) to keep them awake so they can study longer. Large amounts of caffeine for a long period of time can make you:
Lack of sleep and stress from school might make these effects even worse. It’s important for students to find healthy ways to manage stress and get enough sleep.
As your body gets used to caffeine, it needs more and more of it to get the same effect (tolerance). As the amount of caffeine goes up so does the risk of side effects.
You can become mildly dependent on caffeine from regularly drinking 350 mg (about 2 to 4 cups of coffee) a day. You might feel like you can’t function without it, or that you aren’t fully awake until you’ve had caffeine because your mind is groggy or fuzzy.
If you suddenly stop drinking caffeine, you might have withdrawal symptoms like:
Withdrawal symptoms begin 12 to 24 hours after you stop caffeine. Most symptoms go away within a few days.
For more information and to find an addiction services office near you, call the
24-hour Addiction Helpline (Alberta only).
Current as of: August 20, 2019
Author: Poison & Drug Information Service, Alberta Health Services
This material is not a substitute for the advice of a qualified health professional. This material is intended for general information only and is provided on an "as is", "where is" basis. Although reasonable efforts were made to confirm the accuracy of the information, Alberta Health Services does not make any representation or warranty, express, implied or statutory, as to the accuracy, reliability, completeness, applicability or fitness for a particular purpose of such information. Alberta Health Services expressly disclaims all liability for the use of these materials, and for any claims, actions, demands or suits arising from such use.