“I have measured out my life with coffee spoons.”  – T.S. Eliot

Ninety percent of Americans consume some form of caffeine on a daily basis, and it’s the most popular psychoactive substance in the world (largely because it’s safe, legal, and widely available). Different cultures consume caffeine in many different forms, the most common being coffee, tea, espresso, sodas, and, more recently, energy drinks. Caffeine is usually enjoyed for its beneficial effects on wakefulness, attention, and energy, but it also has benefits in other areas of health. Unfortunately, caffeine can also have some undesirable side effects, and a high habitual intake can increase their risk. Below, we examine caffeine’s potential positives and negatives and offer some recommendations for how to maximize its advantages.

How It Works

Caffeine exerts its effects primarily by preventing the chemical adenosine from binding to adenosine receptors. Adenosine is an inhibitory neurotransmitter that suppresses arousal and helps you fall asleep. The blocking of adenosine stimulates the release of the excitatory and mood enhancing neurotransmitters epinephrine and dopamine. These neurotransmitters are largely responsible for caffeine’s awakening and energizing effects.
Coffee, tea, and even chocolate contain various amounts of other caffeine-like chemicals including theobromine, theophylline, and mateine. These chemicals have similar stimulating properties as caffeine, and can elicit stronger or weaker effects for some people (which is why a cup of coffee can keep you up all night, but a cup of tea can have no effect). Sodas and energy drinks use mostly synthetic caffeine anhydrous which looks and acts the same as natural caffeine. These drinks also typically include tea extracts or guarana, another natural source of caffeine.
Some of the most common sources of caffeine and the amount they contain per serving are listed below.

Source Serving size Caffeine (mg)
Caffeine tablet (regular-strength) 1 tablet 100
Excedrin 1 tablet 65
Milk chocolate (10% cacao content) 1 oz 5
Dark chocolate (60% cacao content) 1 oz 30
Drip coffee 8 fl oz 100-150
Starbucks Brewed Coffee 8 fl oz 160
Decaffeinated coffee 8 fl oz 10-15
Espresso 1 oz 40-70
Black tea* 8 fl oz 50-100
Green tea* 8 fl oz 30-70
Yerba mate* 8 fl oz 65-135
Coke, Pepsi, Mountain Dew, etc. 12 fl oz 30-50
Monster energy drink 16 fl oz 80-160
Rockstar energy drink 16 fl oz 80-240
Red Bull energy drink 8.4 fl oz 80

*depends on steep time and variety

How It Can Help

Moderate consumption of caffeine – typically defined as less than 300 mg per day – can have a number of beneficial effects. For most people – especially students and professionals – caffeine is used for its stimulating effects on the brain and body. This includes:

  • Increased energy and vitality
  • Increased alertness and wakefulness
  • Improved mood
  • Enhanced cognitive function – better attention, focus, and faster thought processing

Athletes and fitness enthusiasts also enjoy the stimulating effects of caffeine, especially energy drinks and pre-workout products. Its benefits on exercise include the following:

  • Increased strength and power – likely due to increased nervous system activation and strengthened muscle contractions
  • Increased endurance and time to fatigue – possibly due to a shift to burning more fat and fewer carbohydrates for fuel
  • Enhanced fat loss – caffeine stimulates fatty acid release and fatty acid oxidation, which is why it is included in many popular fat loss products
  • Decreased perception of exercise difficulty – caffeine intake leads to lower reported scores for rating of perceived exertion (RPE)
  • Improved reaction time

Caffeine has numerous other health benefits including the following:

  • Reduced pain – caffeine itself can reduce pain and it can also enhance the effects of other pain killers like acetaminophen
  • Potential treatment for headaches and migraines
  • Treatment for asthma – relaxes smooth muscles in bronchi
  • Treatment for sleep apnea in infants
  • Possible protection against neurodegenerative disorders like Parkinson’s disease, stroke, Huntington’s disease, and multiple sclerosis
  • Prevention of liver disease and the formation of gallstones
  • Possible cancer prevention – by inhibiting the formation of and decreasing the size of both malignant and nonmalignant tumors and inducing apoptosis

Tea and coffee also contain polyphenols, flavanoids, and other biologically active compounds that contribute to enhanced health and vitality and may reduce the risk of chronic diseases like Alzheimer’s disease, diabetes, and certain cancers.

How It Can Hurt

While caffeine can help get you going in the morning, it can also have some undesirable side effects. These effects can depend on intake, tolerance, preexisting conditions, body weight, genetics, and other factors.
The potential negative health affects of caffeine, especially a high consumption, include the following:

  • Increased blood pressure – especially in people with hypertension
  • Increased heart rate
  • Onset or worsening of anxiety, nervousness, and shakiness
  • Difficulty falling sleep or poor quality sleep – if taken too close to bedtime
  • Increased gastric motility and diarrhea
  • Gastric ulcers
  • Low potassium levels (hypokalemia)
  • Increased bone loss in people with osteoporosis
  • Increased risk of miscarriage or pregnancy complications – pregnant women are advised to consume less than 200 mg of caffeine per day
  • Tolerance – as with other psychoactives and stimulants, more of the substance is needed over time to have the same effect. This can increase the risk of side effects.
  • Other effects (click to enlarge):

Caffeine Side Effects1

Source: Wikipedia

What To Do

  • Consume less than 300 mg – or about 3 mg per kilogram of body weight – per day
  • Stick with black coffee or plain tea to avoid excess calories
  • Don’t use caffeine if you are sensitive to it or have any preexisting conditions that can be worsened by it (e.g., hypertension, anxiety, osteoporosis)
  • Limit caffeine to less than 200 mg per day if you are pregnant
  • Don’t consume caffeine close to bed time

Caffeinated beverages have been enjoyed worldwide for centuries in various forms and for various reasons. While caffeine can have some undesirable effects, these are usually due to over-consumption or intolerance. Maintaining a moderate intake is the ideal way to reap the many brain, body, and general health benefits of caffeine.


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