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    Here's How Much Caffeine You Can Safely Have Per Day

    TL;DR: Keep on caffeinating.

    Do you love caffeine but also fear it a little?

    Sally Tamarkin / BuzzFeed News

    Well, good news.

    Everyone give it up for science because a new study determined that healthy adults can drink 400mg of caffeine per day and be A-OK.

    @manualbrewonly / Via

    The study's systematic review methodology expert, Dr. Esther Myer, told BuzzFeed Health via email that the research team (led by Dr. Daniele Wikoff) initially evaluated 5,000 studies, ultimately including 740 in their review, all published between 2001 and 2015.

    The team looked at the effects of caffeine in five areas: acute toxicity (overdose, potential death), cardiovascular effects, bone and calcium effects, behavioral effects, and developmental and reproductive toxicity.

    The consensus: 400mg (or about four 8 oz. cups of coffee) is not associated with adverse effects in healthy individuals.

    In other words, it won't hurt you. Researchers also concluded that healthy pregnant women can safely consume 300mg of caffeine per day and that children and adolescents can safely consume 2.5mg of caffeine per kilogram of body weight per day (so a teen who is 100 lbs. can have about 115mg of caffeine).

    For context, here's the caffeine content in a bunch of popular drinks:

    • Panera single espresso: 73mg

    • Panera iced coffee (20 oz.): 210mg

    • Starbucks tall Pike Place (12 oz.): 235mg

    • Starbucks grande Pike Place (16 oz.): 310mg

    • Starbucks venti Pike Place (20 oz.): 410mg

    • Red Bull (8.4 oz. can): 83mg

    • 5-Hour Energy (1.9 oz.): 215mg

    • Lipton Black Tea (1 bag / 8 oz.): 55mg

    • Coca-Cola (12 oz. can): 34mg

    Up until now, a review of the effects of caffeine hadn't been done since 2003.

    PinkEiga Inc. / Via

    That 2003 study was actually itself a literature review, conducted by Health Canada, that concluded that 400mg of caffeine per day was not associated with adverse health effects.

    But while that study has been widely cited in the years since its publication, Myers pointed out that its research design — called a narrative review — allowed the study authors to select the research and methodology as they conducted the review.

    So, 15 years later (during which time more than 10,000 caffeine-related papers were published), Myers and her team set out to follow up on those findings with a more systematic approach.

    @blackpeopledrinkcoffee / Via

    The research team followed standards from the Institute of Medicine for conducting systematic reviews.

    "The systematic review process is designed to reduce any bias during the process (e.g., decisions on which research to summarize and which to rely more heavily on)," Myers said.

    So, if you consume more than 400mg per day, are you in for a world of hurt?

    @baristamagazine / Via

    Well, the answer is we don't really know AND it'll probably depend on people's own caffeine sensitivity and their overall health. More research is needed to conclude what happens with higher-than-400mg-per-day levels of caffeine consumption. Myers said that only some of the research they reviewed even looked at higher doses of caffeine.

    "We still need more research to better understand the impact of different levels of caffeine intake on adolescents/children, unhealthy populations, acute toxicity (single large dose), inter-individual variability, and other sensitive populations."

    For example, it's important to note that "there will still be individuals who are sensitive to caffeine that can experience adverse effects at lower levels," according to Myers.

    In the meantime, if you're a healthy adult, keep on enjoying those four or so cups per day. (Or that one venti.)

    @thewildbarista / Via

    Or, you know, 1.86 bottles of 5-Hour Energy!

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