Here’s How Much Caffeine Is in a Cup of Coffee

The answer may change depending on the cup.
coffee with callistephus flowers in a jam jar

Knowing how much caffeine is in a cup of coffee can be really helpful when you’re trying to limit your caffeine intake. While being dependent on the stimulant isn’t exactly life-threatening, it can leave you sleepy, grumpy, and jittery. Some people with certain health conditions may find their doctors even suggesting cutting back. And since drinking coffee can become so habitual, it’s easy to go a little overboard without even noticing it.

To be able to monitor caffeine intake, you first have to get a general idea of much caffeine is in a cup of coffee.

According to the USDA, regular, brewed coffee contains about 95 milligrams of caffeine per 8-ounce cup. “This is based on average values of home-brewed and fast-food coffee,” Beth Witherspoon, M.P.H., R.D.N., registered dietitian consultant for Community Coffee Company, tells SELF.

A 2014 study that analyzed caffeine content from multiple sources, including two USDA databases, found that an 8-ounce cup of regular brewed coffee can range in caffeine content from about 75 to 165 milligrams. Flavored coffees tend to have less caffeine, with about 48 milligrams per 8-ounce cup. (Espresso, which you’re probably not drinking a full 8 ounces of at a time, can have as much as 500 milligrams of caffeine per 8-ounce serving.)

There are a lot of things that can influence exactly how much caffeine is in a cup of coffee.

“Caffeine content varies between types and species of coffee beans, and can depend on where the beans were grown, and how the coffee is roasted and then prepared,” Witherspoon says. “All of these factors contribute to the variation in caffeine content between cups of coffee.”

The Mayo Clinic explains that even the same type of coffee from the same coffee shop can vary in caffeine content from day to day. If the beans were ground differently, or an extra scoop was put into the coffee maker, the caffeine content can fluctuate.

Witherspoon adds that light roast coffee usually has more caffeine in it than dark roast. “When measured by volume, light roast beans are denser, weigh more, and thus contain more caffeine than dark roast beans (which lose more water in roasting and weigh less when measured by volume),” she explains.

While most people don’t need to account for every last bit of caffeine they take in daily, a close estimate can help those who are trying to cut back on the stimulant.

Drinking too much caffeine can cause headaches, restlessness, and anxiety in some people. For others, too much after a certain time in the afternoon can cause insomnia.

For the average healthy adult, experts recommend consuming a maximum of 400 milligrams of caffeine each day. That’s three to five 8-ounce cups, depending on specific caffeine content, Witherspoon says. “Individuals should adjust this moderate amount based on how it makes them feel,” she adds.

For example, if you have a hard time falling asleep at night, try cutting yourself off sometime between noon and 2 P.M. to avoid insomnia later on. Everyone has their own level of tolerance, though, so you may need to do some experimenting to find what works for you.

If you’re pregnant or have a heart condition, talk to your doctor about what caffeine limits are appropriate for you. There’s a lot of conflicting evidence about what’s safe during pregnancy, so until more conclusive evidence is available, experts recommend limiting intake to 200 milligrams per day.

These 8 Steps Will Prepare You For a Good Night’s Sleep

Wondering when to stop drinking coffee and using screens to avoid messing with your sleep? How frequently you should wash your sheets?

Scientists have been looking for answers to these questions too.


You can use their answers to guide many of the decisions you make on a nightly basis, from what you drink at night to how often you do laundry.

1. Watch your mid-afternoon caffeine intake.

The Mayo Clinic advises adults to limit their caffeine intake to 400 mg per day, or the equivalent of about two to three coffees.

Caffeine content can differ dramatically based on the type of coffee, however. Just 1.5 cups of Starbucks contains 400 mg of caffeine, while you’d need four cups of McDonald’s drip coffee to equal that amount.

Like too much of anything, excess caffeine comes with risks, including migraine headaches, irritability, upset stomach, and even muscle tremors – so it’s important to know how much you’re getting.

2. On your commute home, don’t agonise over germs.

A team of geneticists made headlines in 2015 for a mission to document all the bacteria on the New York City subway. They turned up nearly 600 different species of microbescrawling around on all those greasy rails.

Before whipping out the hand sanitiser and tissues, keep this in mind: Almost all of the germs they found were completely harmless.

In fact, there’s evidence to suggest that regular exposure to germs helps keep our immune systems healthy by priming it to more easily recognise dangerous microbes in the future.

The idea could partially explain why children who grow up around animals and in rural areas are less likely to develop conditions like asthma than children who don’t.

3. Skip happy hour, or go simply for the food and company.

Alcohol is one of the world’s most widely consumed drugs, but drinking even small amounts – as little as one glass of wine or beer a day – has been linked with a host of negative side effects, including cancer.

In November, the American Society of Clinical Oncology, a group of the nation’s top cancer doctors, released an unprecedented warning in which it told Americans to drink less.

“ASCO believes that a proactive stance by the Society to minimise excessive exposure to alcohol has important implications for cancer prevention,” the statement said.

So at your next happy-hour event, consider skipping the booze or doing something else.

4. Stay hydrated.

Staying hydrated is vital. Our bodies are 60 percent water, and not getting enough can lead to headaches, fatigue, and even overeating. Still, contrary to popular opinion, you don’t necessarily need to drink eight glasses of water a day.

Instead, your daily hydration requirement can change based on several factors, from how much you worked out that day to the weather outside.

Certain foods are also a good water source, so eating more of them may mean you need to drink less. Cauliflower, eggplant, peppers, and spinach are all 92 percent water. Carrots, green peas, and even white potatoes are more than 79 percent.

5. Take breaks from screens to avoid eye strain.

Many of us go from starting at computers to staring at our phones, and as a result our eyes are often dry, itchy, blurry, or irritated. Ophthalmologists call this condition “digital eyestrain.”

To avoid it, make sure you’re drinking (and blinking) enough and avoid reading your phone under the glare of a lamp. You can also practice what’s known as the 20-20-20 rule.

Every 20 minutes, look at something at least 20 feet away for 20 seconds. This will allow your eyes to rest, Rahul Khurana, the clinical spokesman for the American Academy of Ophthalmologists told my colleague Kevin Loria.

6. If you go out for dinner, plan on taking up to a third of it home.

The baseline portion sizes of our snacks and meals have ballooned over the past 40 years – even the plates and cups we serve them on have gotten noticeably bigger.

The average size of many of our foods – whether fast food, sit-down meals, or even items from the grocery store – has grown by as much as 138 percent since the 1970s, according to data from the American Journal of Public Health, the Journal of Nutrition, and the Journal of the American Medical Association.

So be mindful of portion sizes, and if you’re eating out, consider taking anywhere from a third to half of it to go.

7. Put away screens for at least 30 minutes before bedtime.

The blue light that illuminates our screens also tamps down on the production of melatonin, a key hormone our brains use to tell our bodies to start preparing for sleep.

That’s something you don’t want to be doing at night, especially right when you’re heading to bed. Experts recommend at least 30 minutes of no-screen time before bedtime.

8. Before you tuck in for the night, make sure your sheets are clean.

Our beds can blossom into a “botanical park” of bacteria and fungus in as little as a week, New York University microbiologist Philip Tierno told Business Insider.

The combination of sweat, animal dander, pollen, soil, lint, dust-mite debris, and plenty of other things is enough to make anyone sick, let alone someone with allergies. So clean your sheets at least once every seven days.

Blood Levels of Caffeine May Help Diagnose Parkinson’s

Blood levels of caffeine and its metabolites may be promising diagnostic biomarkers for early Parkinson’s disease, Japanese researchers reported.

Unrelated to total caffeine consumption or disease severity, serum levels of caffeine and nine of its downstream metabolites were significantly lower in patients with early Parkinson’s, Shinji Saiki, MD, PhD, of Juntendo University School of Medicine in Tokyo, and colleagues reported online in Neurology.

There were no significant genetic variations in the enzymes metabolizing caffeine between patients and controls.

Caffeine concentrations also were significantly decreased in Parkinson’s patients with motor fluctuations than in those without motor complications. However, patients in more severe disease stages did not have lower levels of caffeine, “suggesting that the decrease in caffeine metabolites occurs from the earliest stages of Parkinson’s,” David G. Munoz, MD, of the University of Toronto, and Shinsuke Fujioka, MD, of Fukuoka University in Japan, wrote in an accompanying editorial.

Some previous reports have suggested an inverse association between daily caffeine consumption and reduced risk of developing Parkinson’s, although a recent randomized controlled trial found no benefit to caffeine intake for Parkinson’s symptoms.

Mechanistically, caffeine could improve motor symptoms by antagonizing adenosine 2A receptors (A2A-Rs), but changes in the entire caffeine metabolic pathway in Parkinson’s patients are unclear.

In this study, researchers examined blood samples of 108 patients with idiopathic Parkinson’s disease and 31 age-matched healthy controls, separating caffeine and 11 downstream metabolites by high-performance liquid chromatography. All Parkinson’s patients had been treated at Juntendo University Hospital; on average, they had mild to moderate disease severity. Age, sex, and total caffeine intake were similar for both groups.

The researchers also recruited an additional 51 healthy controls and 67 Parkinson’s patients for gene analysis, screening for mutations in caffeine-associated genes by direct sequencing.

Blood levels of caffeine and nine of its 11 metabolites were lower in Parkinson’s patients than in controls (P<0.0001). The difference could be used to separate patients from controls reliably, with an area under the receiver operating characteristic curve of 0.98.

Analyses of caffeine-related genes showed no significant differences between patients and controls. The researchers saw no significant genetic variations in CYP1A2 or CYP2E1, the encoding cytochrome P450 enzymes primarily involved in metabolizing caffeine, between the groups. They found no associations between disease severity and single nucleotide variants of the ADORA2A gene, which encodes A2A-R.

They also detected no correlations between levodopa equivalent doses and absolute concentrations of caffeine and its metabolites.

One reason why early Parkinson’s patients had decreased caffeine levels may be related to intestinal absorption, the authors suggested. Gastrointestinal problems like constipation can affect up to 80% of Parkinson’s patients, sometimes preceding symptom onset by years, and a recent analysis showed that fecal microbial flora is altered in patients with Parkinson’s.

 “Although constipation and fecal bacterial change are predominantly attributed to large intestine function, caffeine absorption mainly occurs in the small intestine, where bacterial overgrowth in Parkinson’s is associated with levodopa malabsorption leading to motor fluctuations,” Saiki and colleagues observed.

Another explanation might be anti-parkinsonian agents.

“There is an elephant in the room: almost all patients with Parkinson’s were receiving treatment,” wrote Munoz and Fujioka. “The authors address this issue by finding no association between levels of caffeine metabolites and levodopa equivalent doses, but it is obvious that the validity of the study hangs on this point.”

“If a future study were to demonstrate similar decreases in caffeine in untreated patients with Parkinson’s, or persons with prodromal signs of Parkinson’s including REM behavior disorder, many of whom would be expected to develop Parkinson’s, the implications of the current study would take enormous importance,” they continued. This could lead to an easy test for early diagnosis or point to a basic mechanism of Parkinson’s pathogenesis.

One limitation of this study is that it did not include severe Parkinson’s cases; its reduced power may have limited the researchers’ ability to detect an association between disease severity and caffeine levels. Despite the lack of correlation between levodopa equivalent doses and caffeine concentration, Parkinson’s medications still might have affected metabolism, the authors added.

“Similar to a recent study showing progressive decreases in caffeine metabolites with disease exacerbation, de novo Parkinson’s studies including larger study populations and studies on differential diagnostic values among patients with Parkinson’s and other parkinsonian patients should be performed,” they wrote.

All the ways caffeine affects your body in one handy infographic .

CaffeineInfographic small

Caffeine is the most widely used drug in the world, but most of us don’t really know or care exactly what goes on inside our bodies when we drink our morning cup of coffee. Obviously it help us wake up and focus, but caffeine actually has some much broader much broader, and in some cases, more surprising effects. This Business Insider infographic (high res version here) summarises them all for you, so that you can really appreciate how much your flat white does for you.
For starters, let’s set the record straight on how much caffeine your body can really handle. For most of us that’s around 400 milligrams per day, or five Red Bulls (interesting fact: the amount of caffeine you can drink is actually determined by your genes) but if you’re anything like me, that amount would make you incredibly jittery.

That’s because when caffeine hits our bloodstreams, around one to two hours after being ingested, it increases our blood pressure and tells our adrenal glands to pump out more adrenaline, which makes us irritable and emotionally charged.

On the plus side, it also triggers the release of dopamine and glutamine in the brain, which help boost mood and reduce the risk of depression. It also blocks a molecule called adenosine in the brain, to stop us from feeling sleepy.

In addition to improving focus, studies have shown that caffeine also has the ability to improve people’s memories, although it seems that the effects aren’t so impressive for people who are already hooked on it.

Not mentioned on this infographic is the fact that, for many of us, coffee also makes us poop. This effect is linked to the drink itself, rather than caffeine, but research has shown that there’s a pretty fascinating reason for why our morning cup of coffee sees us running to the bathroom.

The sad part of all of this is that the effects of caffeine do wear off, usually after around five or six hours. Although for many of us, it feels a lot quicker, and we’re usually reaching for our next cup pretty soon after our first.

Watch the video. URL:

Does caffeine make depression worse?

steaming cup of coffee on table with iPad
There’s no clear link between caffeine intake and depression. However, caffeine intake and depression may be linked indirectly for people who are particularly sensitive to the effects of caffeine or who have too much caffeine.

  • Caffeine can cause sleep problems that affect mood.Caffeine can make it harder to fall asleep and stay asleep. Lack of sleep can worsen depression. If you have trouble sleeping, don’t drink caffeinated beverages late in the day. Some people need to limit the caffeine they have to only in the morning, or quit drinking caffeinated beverages completely to avoid sleep problems. Also, anxiety and depression often occur together, and caffeine can worsen anxiety.

There’s no clear link between caffeine intake and depression. However, caffeine intake and depression may be linked indirectly for people who are particularly sensitive to the effects of caffeine or who have too much caffeine.

  • Caffeine can cause sleep problems that affect mood.Caffeine can make it harder to fall asleep and stay asleep. Lack of sleep can worsen depression. If you have trouble sleeping, don’t drink caffeinated beverages late in the day. Some people need to limit the caffeine they have to only in the morning, or quit drinking caffeinated beverages completely to avoid sleep problems. Also, anxiety and depression often occur together, and caffeine can worsen anxiety.
  • Stopping abruptly can worsen depression. If you regularly drink caffeinated beverages, quitting can cause a depressed mood until your body adjusts. It can also cause other signs and symptoms, such as headaches, fatigue and irritability.

If you have depression, consider limiting or avoiding caffeine to see if it helps improve your mood. To lessen these withdrawal effects, gradually reduce the amount of caffeinated beverages you drink.



It’s no secret that slugging down caffeinated drinks in the evening can disrupt sleep.

But a new study led by the University of Colorado Boulder and the Medical Research Council’s Laboratory of Molecular Biology in Cambridge, England shows for the first time that evening caffeine delays the internal circadian clock that tells us when to get ready for sleep and when to prepare to wake up. The research team showed the amount of caffeine in a double espresso or its equivalent three hours before bedtime induced a 40-minute phase delay in the roughly 24-hour human biological clock.

The study also showed for the first time how caffeine affects “cellular timekeeping” in the human body, said CU-Boulder Professor Kenneth Wright, who co-led the study with John O’Neill of the Medical Research Council’s Laboratory of Molecular Biology (LMB) in Cambridge. While it has been known that caffeine influences circadian clocks of even primitive creatures like algae and fruit flies, the new study shows that the internal clocks in human cells can be impacted by caffeine intake.

“This is the first study to show that caffeine, the mostly widely used psychoactive drug in the world, has an influence on the human circadian clock,” said Wright, a professor in CU-Boulder’s Department of Integrative Physiology. “It also provides new and exciting insights into the effects of caffeine on human physiology.”

A paper on the subject led by Wright and O’Neill is being published online in the Sept 16 issue of Science Translational Medicine.

For the study the team recruited five human subjects, three females and two males, who went though a double-blind, placebo-controlled 49-day protocol through CU-Boulder’s Sleep and Chronobiology Laboratory, which is directed by Wright. The subjects were tested under four conditions: low light and a placebo pill; low light and the equivalent of a 200-milligram caffeine pill dependent on the subject’s weight; bright light and a placebo pill; and bright light and the caffeine pill.

Saliva samples of each participant were tested periodically during the study for levels of the hormone melatonin, which is produced naturally by the pineal gland when directed to do so by the brain’s “master clock.” The master clock is re-set by exposure to light and coordinates cellular clocks throughout the human body. Melatonin levels in the blood increase to signal the onset of biological nighttime during each 24-hour period and decrease at the start of biological daytime, said Wright.

Those who took the caffeine pill under low-light conditions were found to have a roughly 40-minute delay in their nightly circadian rhythm compared to those who took the placebo pill under low light conditions, said Wright. The magnitude of delay from the caffeine dose was about half that of the delay induced in test subjects by a three-hour exposure to bright, overhead light that began at each person’s normal bedtime.

The study also showed that bright light alone and bright light combined with caffeine induced circadian phase delays in the test subjects of about 85 minutes and 105 minutes respectively. There were no significant differences between the dim light/caffeine combination and the bright light/placebo combination. Nor were there significant differences between the bright light/placebo and bright light/caffeine combinations. The results may indicate a “ceiling” was reached in the phase delay of the human circadian clock due to the external factors, Wright said.

In addition, researchers at O’Neill’s lab at the LMB in Cambridge used “reporter” genes that made cells glow when the clock genes were expressed to measure changes caused by caffeine. O’Neill’s group showed that caffeine can block cell receptors of the neurotransmitter adenosine, which normally promotes sleep and suppresses arousal.

The results may help to explain why caffeine-drinking “night owls” go to bed later and wake up later and may have implications for the treatment of some circadian sleep-wake disorders, said Wright.

The new results could benefit travelers. Properly timed caffeine use could help shift the circadian clocks of those flying west over multiple time zones, said Wright.

In a 2013 study, Wright and his research team showed one week of camping in the Rocky Mountains with no artificial light, not even flashlights, synchronized the circadian clocks of the eight study subjects with the timing of sunrise and sunset.


All the ways caffeine affects your body in one handy infographic .

No wonder we’re so addicted.

CaffeineInfographic small

Caffeine is the most widely used drug in the world, but most of us don’t really know or care exactly what goes on inside our bodies when we drink our morning cup of coffee. Obviously it help us wake up and focus, but caffeine actually has some much broader much broader, and in some cases, more surprising effects. This Business Insider infographic (high res version here) summarises them all for you, so that you can really appreciate how much your flat white does for you.

Watch the video. URL:

How Too Much Caffeine Drove One Woman to Become Manic .

Coffee is one heck of a drug. It’s addictive and, as most of us know, when some people don’t get their daily dose of Joe, they get irritable. But what happens when you get too much of that morning motivator? Caffeine intoxication.

Agata Blaszczak Boxe from Braindecoder reported on an interesting case of a woman who became manic after consuming quite a bit of caffeine. Dr. Julia Tatum Krankl, a psychiatrist at the UCLA Semel Institute for Neuroscience and Human Behavior, and her team of researchers wrote a paper on the 2013 case, which was published in this month’s issue of The American Journal of Addictions. They write that they observed “multiple episodes of caffeine-induced mania with psychotic features and met criteria for caffeine use disorder.”

The Diagnostic and Statistical Manual of Mental Disorders (the DSM-5) originally defined the temporarily self-induced mental disorder, caffeine intoxication, back in 2013. The list of symptoms is quite long, ranging from restlessness, nervousness, excitement, and rambling speech to muscle twitching, sleeplessness, and irregular heartbeat.


For a 69-year-old woman in the summer of 2013, the issues began when she started pounding down 32 ounces of coffee per day. In the fall, researchers say she upped that dose to around 840 mg of caffeine per day — more than twice as much as the Dietary Guidelines Advisory Committee deemed safe in their recent and first report that included a discussion on coffee.

Days after going on this coffee bender, in the hopes that it would help regulate her stress, she landed in the hospital with symptoms of mania, as reported by researchers. They observed fluctuations in her mood, restlessness, and rapidity in her speech.

Krankl explained how they ruled out any other possibilities:

“The reason why we thought that the cause of her mania was caffeine was that, as she increased her caffeine use, the mania symptoms started and got worse. And as she decreased her caffeine use, her mania symptoms went away.”

The researchers report, however, after she was discharged, she began her coffee-drinking habits again, though, to a lesser extent. They estimate that she consumed 526 mg of caffeine a day. Her mental health began to deteriorate once more, becoming paranoid of the doctors trying to help her regulate.

The woman did eventually get a hold of her issue, reducing her consumption to around 95 mg of caffeine per day with the help of addiction counseling.

The researchers believe that “[this] case supports evidence that caffeine use disorder should be considered for inclusion in future diagnostic manuals as a potential drug of abuse pending additional research.”

Caffeine plays with our internal chemistry, affecting the neurotransmitter dopamine in the brain and playing with parts of us that cause us to go for “just one more cup.” I know if I don’t regulate, I begin to become anxious and restless myself.

Caffeine’s effects differ when sugar is included .

Consuming caffeinated or sugary drinks can affect the body’s metabolism, causing changes in heart and respiratory rate and weight gain. The results of a new study exploring whether individuals respond differently to caffeinated drinks that do or do not contain sugar and to sugar alone are published in Journal of Caffeine Research: The International Multidisciplinary Journal of Caffeine Science.

The article entitled “Caffeine With and Without Sugar: Individual Differences in Physiological Responses During Rest“, by Elaine Rush, PhD and coauthors, Auckland University of Technology (Auckland, New Zealand), describes a study in which heart rate and carbon dioxide production (as a measure of respiration) were measured 30 minutes before and after individuals consumed a defined quantity of sugar, caffeine, or sugar and caffeine. Responses to the different treatments varied widely among individuals.

“Given the caveat that sugar itself affects brain reward just as caffeine does, and this effect will in itself cause variations, this is still an essential paper for the scientist and the lay person to read,” says Patricia A. Broderick, PhD, Editor-in-Chief of Journal of Caffeine Research, Medical Professor in Physiology, Pharmacology & Neuroscience, The Sophie Davis School of Biomedical Education, The City College of New York, The City University of New York, and Adjunct Professor in Neurology, New York University Langone Medical Center and Comprehensive Epilepsy Center.

Caffeine Side Effects And More: How The World’s Most Popular Drug Can Affect Your Health

According to Villanova University, 90 percent of Americans have some caffeine every day. While most of us are aware of the stimulative effect the world’s most widely used drug has on our brain, its effects on other parts of our body are not as widely known. Here’s a short list of some of the most common effects caffeine consumption can have on our health.


Bathroom Habits

No, it’s not just you who has to run to the bathroom before you’ve even finished your first cup of coffee. Caffeine has both a diuretic and laxative effect that will keep you in and out of the toilet for the better half of the morning.

As a diuretic, caffeine causes the consumer to expel more water than was in the original beverage. As most things in life, caffeine’s diuretic effect is largely dependent on how much you intake. For example, if you only have 3mg of caffeine, there’s absolutely no diuretic effect, and you would pee as you normally would. Drinking larger amounts such as the 95-200mgs in an average cup of coffee? Then you better start looking for a toilet fast.

ASAP Science explained that your pituitary gland controls the release of the anti-diuretic hormone (ADH). In normal circumstances, ADH travels to the kidneys where they stimulate the retention of water to keep our body at a happy medium of hydration. Caffeine inhibits the release of ADH, which results in less water being reabsorbed into your body and more being converted into urine. Caffeine belongs to a group of chemicals called xanthine, and these are able to block the body’s reabsorption of sodium. When this occurs, rather than returning to the blood stream, the sodium stays in the fluid where it becomes urine.

Just as caffeine increases our urge to urinate, it also makes us poop. Believe it or not, scientists aren’t really sure why. One theory is that the drug affects the tissue that lines our stomach and small intestines, while others think that caffeine promotes the release ofhormones that control the colon’s activities.

However, caffeine doesn’t just stop at making us poop; it also changes the texture of our bowel movements, making them looser, because, as we previously learned, caffeine prevents the body from reabsorbing water. This can result in a mean case of diarrhea if you’re not careful with your caffeine intake!

Caffeine And Athletes

The American College of Sports Medicine found that caffeine is able to enhance endurance performance by increasing the release of adrenaline into the blood. This release in turn stimulates the release of free fatty acids from the fat tissue and/or skeletal muscle. This creates extra fat early in the exercise, which spares extra energy to be used later in the exercise. The effect is that the athlete doesn’t tire out as quickly.

The ACSM concluded that ingestion of 3-9mg of caffeine per kilogram of an athlete prolonged endurance by approximately five minutes. Caffeine was believed to be so advantageous to athletes that until 2004 Olympians could be thrown out of a competition for having too much of it in their urine, Mens Health reported.

Caffeine may not be best for all athletes, however. It has been found to impair the consumers’ reflexes and decrease their reaction time. A study gave subjects caffeine before their patellar ligament reflex (also known as that tap on your knee that causes your leg to jerk up), and results showed that only 6mg of caffeine per kilogram of weight was able to “significantly lengthen reflex time.”

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