How Many Hours Does Caffeine Keep You Awake?

If you're one of the many people who rely on caffeine to keep them awake during the day, you may also turn into a person who has trouble falling asleep at night. Your afternoon coffee may ultimately affect your lifestyle.

According to the U.S. National Library of Medicine, caffeine is a bitter substance that's found in more than 60 plants, including coffee beans, tea leaves, kola nuts (used to flavor cola) and cacao pods. Most people consume caffeine from drinks. Depending on what you're drinking, the caffeine content may vary. Some common drinks with caffeine include:

• An 8-ounce cup of coffee: 95-200 milligrams
  
• An 12-ounce can of cola: 35-45 milligrams
• An 8-ounce energy drink: 70-100 milligrams
• An 8-ounce cup of tea: 14-60 milligrams

In a May 2017 review published in ​Frontiers in Psychiatry​, researchers looked into the safety of ingested caffeine in healthy and vulnerable populations. They reported that caffeine is relatively safe for healthy adults. One of the researchers who conducted these studies assisted in legal cases involving caffeine-containing energy drinks, so the findings may be biased.

In some vulnerable populations, such as pregnant women, children and people with mental illnesses, this substance may cause impairments in cardiovascular function and sleep, according to the above review. However, excess caffeine consumption is considered potentially harmful by most health professionals.

​Read more:​ What Really Happens to Your Body When You Have Caffeine

Caffeine is one of the most popular drugs in the world as people consume it daily in coffee, tea, energy drinks, chocolate, soda and some foods or supplements. According to the National Sleep Foundation, this compound enters the bloodstream through the stomach and the small intestine. It can have a stimulating effect in as little as 15 minutes after it is consumed.

You don't need a caffeine half life calculator— just remember that once ingested, it can take about six hours for one half of the caffeine to be eliminated. This is why it may be hard for people who drink an afternoon coffee or have coffee at night to fall asleep. As a rule of thumb, it's recommended to avoid coffee after 3 p.m. (so no coffee at night!) as the caffeine will stay in your system for up to six hours after that.

The Mayo Clinic states that caffeine may cause a short but significant increase in blood pressure because it is believed to block a hormone that keeps your arteries widened. However, people who drink caffeinated drinks daily may develop a tolerance to this substance.

Consuming moderate amounts of caffeine doesn't seem to have long-term harmful effects. However, drinking too much of it (1,000 milligrams or more) regularly may result in reproductive issues, heartburn and irregular bowel habits, according to the University of Michigan Health Service.

​Read more:​ Long-Term Effects of Caffeine

The USDA Dietary Guidelines for Americans 2015-2020 advise that moderate coffee consumption, which is three to five 8-ounce cups per day, can be incorporated in a healthy lifestyle since it's not associated with an increased risk of major chronic diseases. However, people who currently don't consume coffee or other caffeinated drinks are not encouraged to start.

In case you have trouble sleeping at night due to your afternoon coffee, or if your daily caffeine intake is too high, it may be time to cut back and talk to a doctor. The Cleveland Clinic advises that it's important to always cut back slowly instead of all at once. This may help prevent unpleasant side effects like migraines and nausea.

If you feel like you need caffeine to wake up in the morning, try drinking one or two cups in the earlier hours. Having a coffee past 3 p.m. may keep you awake at bedtime. Another option is to drink decaffeinated coffee, which only contains a small amount of caffeine.