Coffee carries more secondhand "facts" than almost anything else people put in their mouths. Some of these ideas go back decades. A few are half-true. Most fall apart the moment someone actually checks.
Here are six of the most common claims, checked against the research that actually exists.
Myth: Coffee dehydrates you
This one feels intuitive. Caffeine is a mild diuretic, so it seems to follow that coffee should leave you drier than you started.
A 2014 study in PLoS One tested this directly. Fifty men who habitually drank three to six cups of coffee a day were tracked through two three-day trials, one with coffee and one with water only, while everything else about their diet and activity stayed controlled.[1]
The result: moderate coffee intake "provides similar hydrating qualities to water." Total body water didn't differ between the two trials, and the researchers found no evidence that regular coffee drinking causes dehydration.[1]
Fact: For people who drink it regularly, coffee counts toward daily fluid intake much like any other drink. The diuretic effect is real but mild, and habitual drinkers adapt to it.
Myth: Coffee stunts your growth
This is one of the oldest coffee myths, and it's almost entirely detached from its original source.
The idea traces back to studies from decades ago linking coffee drinking with lower bone density, mostly in older adults. Coffee drinkers in those studies also tended to drink less milk, a major calcium source, so the real variable may have been reduced calcium intake rather than caffeine itself. Science writer Mark Pendergast, author of Uncommon Grounds, says the sheer volume of conflicting coffee studies over the years makes it all "confusing," which is part of why myths like this one don't fully go away.[2]
Registered dietitian Duane Mellor of Aston University makes a similar point: the caution doctors give pregnant women about caffeine doesn't translate into "caffeine stops children from growing." Those are different situations with different mechanisms.[2]
Fact: There's no evidence that caffeine itself shortens bones or blocks growth. That said, the American Academy of Pediatrics still recommends young children avoid caffeine and that adolescents limit it, mainly because of its effects on sleep, anxiety, and blood pressure, not growth. A sugary iced coffee drink is a bigger nutritional concern than the caffeine in it.
Myth: Coffee is bad for your heart
For a long time this was treated as settled. It isn't, and the evidence has moved in the opposite direction.
A 2026 American Heart Association scientific statement, reported by the Harvard T.H. Chan School of Public Health, concluded that drinking up to roughly five cups of coffee a day (about 400 mg of caffeine) is safe for most adults and may lower the risk of heart failure, heart disease, and stroke.[3]
The statement's authors note the likely benefit comes partly from other compounds in coffee, not caffeine alone.[3]
Fact: Moderate coffee drinking is not a heart risk for most healthy adults and may be mildly protective. The exception is high-dose caffeine from sources like energy drinks, which the same research flags as a real risk for blood pressure and heart rhythm issues at the doses typically consumed.
Myth: Caffeine is as addictive as hard drugs
Coffee drinkers joke about "needing" their morning cup, and the withdrawal headache is real. But that's a different thing from the addictive potential of drugs like nicotine or cocaine.
A 2020 study in the Journal of Caffeine and Adenosine Research looked at this directly. Caffeine use disorder was added to the DSM-5, the standard reference psychiatrists use, but only in Section III, as "a condition for further study," not as a formal diagnosis. The proposed criteria are deliberately more conservative than for other substances, specifically to avoid overdiagnosing something as common as coffee drinking.[4]
In a survey of just over 1,000 U.S. adults, 8% met all three proposed criteria: a persistent desire or failed attempts to cut down, continued use despite problems, and withdrawal.[4]
Fact: Caffeine does produce real physical dependence and withdrawal (headache, fatigue, irritability), which is why quitting cold turkey feels bad. But it isn't classified alongside substances like nicotine or cocaine, and the researchers who study it deliberately set a higher bar before calling it a disorder.
Myth: Dark roast has more caffeine than light roast
This feels like it should be true. Dark roast tastes stronger and more bitter, so it's a natural assumption that it's more caffeinated too.
A 2017 study in Scientific Reports measured caffeine content directly across roast levels, grind sizes, and brewing methods. The finding ran the other way, at least for cold brew: medium roast samples measured higher caffeine than dark roast samples at a coarse grind, though the difference disappeared at a finer, medium grind. The study didn't report a separate caffeine comparison by roast for hot brew.[5]
The explanation isn't settled. The study's own authors note that caffeine concentrations don't respond to roasting temperature the way chlorogenic acid does, and the roasting literature is genuinely inconsistent here: some prior research found the opposite relationship, with higher roasting temperatures correlating with more caffeine, not less. What the 2017 study is confident about is the measurement itself, not why it happens.[5]
Fact: Roast level is a poor predictor of caffeine content. Bean variety, brewing method, and how much coffee you actually use matter more than whether the beans are light or dark.
Myth: Coffee sobers you up
This is the myth that refuses to die, mostly because the feeling of being "more alert" after a strong coffee is real.
The National Institute on Alcohol Abuse and Alcoholism addresses this directly: "Caffeine may help with drowsiness but not with the effects of alcohol on decision-making or coordination." Its broader conclusion is blunt: "there's no way to sober up faster."[6]
Caffeine doesn't change how quickly the liver metabolizes alcohol, and it doesn't lower blood alcohol concentration. It can make someone feel more awake while their coordination and judgment are still just as impaired.
Fact: Coffee can mask tiredness, which is arguably more dangerous than feeling tired, since it can make an impaired person feel ready to, say, drive. Only time clears alcohol from the body.
The pattern across all six
Most coffee myths share a common structure: a real but narrow finding gets stretched into a sweeping claim, and the stretched version is what survives. Coffee's diuretic effect is real, just not strong enough to dehydrate a regular drinker. The old bone-density studies were real, just confounded by something other than caffeine. The feeling of being wired after a strong coffee is real, it just isn't the same as being sober.
None of this means coffee is risk-free or that moderation doesn't matter. It means the specific reasons people usually give for caution are often not the right ones.
Sources
Health claims adapted from the research and guidance below. Sources checked October 2026. Cup Taste is not affiliated with or endorsed by PLoS One, Live Science, the American Heart Association, Harvard T.H. Chan School of Public Health, the Journal of Caffeine and Adenosine Research, Scientific Reports, or the National Institute on Alcohol Abuse and Alcoholism.
[1] Killer, S.C., Blannin, A.K., Jeukendrup, A.E. No Evidence of Dehydration with Moderate Daily Coffee Intake: A Counterbalanced Cross-Over Study in a Free-Living Population. PLoS One, 2014;9(1):e84154. https://doi.org/10.1371/journal.pone.0084154
[2] Plackett, B. Does coffee really stunt kids' growth? Live Science. Includes commentary from Mark Pendergast and Duane Mellor, RD (Aston University), and guidance from the American Academy of Pediatrics. https://www.livescience.com/coffee-does-not-stunt-growth.html
[3] American Heart Association, 2026 scientific statement on caffeine and cardiovascular health, reported by Harvard T.H. Chan School of Public Health. https://hsph.harvard.edu/news/up-to-five-cups-of-coffee-a-day-may-benefit-heart-health/
[4] Sweeney, M.M., Weaver, D.C., Vincent, K.B., Arria, A.M., Griffiths, R.R. Prevalence and Correlates of Caffeine Use Disorder Symptoms Among a United States Sample. Journal of Caffeine and Adenosine Research, 2020;10(1):4-11. https://doi.org/10.1089/caff.2019.0020
[5] Fuller, M., Rao, N.Z. The Effect of Time, Roasting Temperature, and Grind Size on Caffeine and Chlorogenic Acid Concentrations in Cold Brew Coffee. Scientific Reports, 2017;7:17979. https://doi.org/10.1038/s41598-017-18247-4
[6] National Institute on Alcohol Abuse and Alcoholism. The Truth About Holiday Spirits. https://niaaa.nih.gov/publications/brochures-and-fact-sheets/truth-about-holiday-spirits