Caffeine is a mild stimulant of the central nervous system (1). It may help prevent sleepiness in some people (1). It may slightly increase the effect of analgesics, such as aspirin or acetaminophen (43). It slightly widens vessels, which may help in migraine, so it is added to certain migraine medications (3).
Some people may experience caffeine side effects after as little as 2-3 cups of coffee:
Some people may have symptoms of caffeine intoxication after two cups of coffee (250 mg caffeine), many people after about six cups (600 mg caffeine), but some do not have any symptoms even after 900 milligrams of caffeine (2).
Possible symptoms of caffeine overdose:
Withdrawal symptoms typically appear 12-24 hours after the last caffeine dose in individuals who consume caffeine at least three days in the row (16); in some individuals, withdrawal symptoms may appear in as little as 3 hours and may last for a week (21). Main symptoms include headache, restlessness, fatigue, apathy, weakness, flu-like symptoms with stuffy nose (15).
Many people quickly (in few days of regular consumption) develop tolerance to both beneficial effects (alertness) and harmful effects (e.g increase of blood pressure, insomnia) of caffeine (28,29).
TABLE: Caffeine content of coffee, tea, coke, energy drinks, chocolate (2,17,18,19,20,21,28)
|SOURCE||AMOUNT OF CAFFEINE in milligrams (mg)|
|Espresso, restaurant style (1 oz = 30 mL)||40 (30-90)|
|Instant (8 oz = 1 cup = 240 mL)||70 (30-170)|
|Brewed, Arabica (8 oz = 1 cup = 240 mL)||100 (70-120)|
|Fast-food-size coffee (16 oz = 2 cups = 480 mL)||125 (100-330)|
|Herbal and fruit tea||0|
|Green, black, white, oolong tea (8 oz = 1 cup = 240 mL)||30 (15-110)|
|Cola (including diet coke), soda, root beer; caffeinated (12 oz can = 355 mL)||40 (30-120)|
|1 can (4-16 oz = 120-480 mL) NOTE: Smaller can does not necessarily mean less caffeine||80 (30-350)|
|Milk chocolate (1 oz = 28 g)||6|
|Dark chocolate, 70-85% cacao (1 oz = 28 g)||23|
|Dark chocolate-coated coffee jelly beans (28 pieces = 40 g)||335|
Certain prescription or over-the counter medicines, such as analgesics, medications for migraine, diuretics, weight-loss pills, dietary supplements and stimulants may contain up to 400 milligrams caffeine per tablet or capsule (22,23). Certain herbal products containing yerba mate, guarana, green tea extracts and kola nut, contain caffeine. Consult your doctor before using any medication containing caffeine.
Exact effects of caffeine on the growing baby are still not known, so doctors often advise against consuming caffeinated beverages during pregnancy. Many doctors recommend women to limit caffeine intake to 200 mg caffeine per day (about two cups of coffee; four cups of tea; five 12 oz cans of cola) to avoid eventual harms (30,31,38).
The results of studies about the effect of caffeine intake during pregnancy on birth outcomes are conflicting. Below, few studies are mentioned:
Two studies in the U.S. (y. 2009 and 2011) did not reveal any association between caffeine intake during pregnancy and cleft palate or other birth defects in the babies (34,45).
Caffeine is a pregnancy category C drug, which means that in animal studies, caffeine had adverse effects on the fetus, but no well controlled studies in humans have been done (47). This means that harmful effects of caffeine on the human fetus have not been firmly proven, but they currently cannot be ruled out.
One large study in Denmark (y.2007-2010) (35) and one 2010 study in Saudi Arabia (37) and some other studies (42) have found no significant association between caffeine intake and fertility.
Fact 1: Caffeine can get across the placenta and increase baby’s heart rate (46).
Fact 2: Some, but not all, studies have found association between caffeine consumption during pregnancy, miscarriages and and low birth in the babies.
Myth 1: Caffeine during pregnancy is always harmful for the baby. The fact is that not all studies have found harmful effects of caffeine on the babies.
Myth 2: Caffeine leads to irritability and ADHD (Attention Deficit Hyperactivity Disorder) in the newborn child. This association has not been proven.