The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.
Individuals who metabolize caffeine differently may be at increased risk for side effects.
Stomach irritation or upset, nausea, diarrhea, abdominal pain, and loss of bowel control may occur with caffeine intake. Caffeine may increase levels of stress hormones (including cortisol, epinephrine, and norepinephrine) and stimulate ulcer formation. Coffee may increase stomach acid production and increase the incidence of acid reflux heartburn, gastroesophageal reflux disease (GERD), regurgitation, and difficult or painful swallowing. Coffee may also speed up the process of stomach emptying, possibly leading to injury of the intestinal tissue.
Other possible side effects of caffeine include agitation, airway inflammation, anxiety, daytime sleepiness, dehydration, delayed conception, depleted carbon monoxide levels in the blood, depression, difficulty thinking clearly, display of anger, drowsiness, fatigue, headaches, hyperactivity, impaired alertness and attention, impaired memory retention, increased chronic back pain, increased frequency and severity of premenstrual syndrome (PMS), increased occurrence of gallstone polyps, increased risk of Parkinson's disease and multiple sclerosis, increased risky behavior (including binge drinking, drinking and driving, sexual activity, and suicidal acts), irritability, jitteriness, lack of energy, loss of B vitamins, mild delirium, nervousness, overactive reflexes, panic attacks, poor feeding, reduced blood potassium levels, reduced semen quality, restlessness, shortened menstrual cycle, sleep disturbances, suppressed immune function, sweating, teeth grinding, wakefulness, and worsened liver damage,
Caffeine is a known stimulant agent and may increase heart rate or cause irregular heartbeats. Caffeine may also be associated with adverse effects on blood vessel function and increased risk of ischemic stroke (blocked blood flow to the brain). Use cautiously in people with a known history of abnormal heart rhythms.
Caffeine is a known diuretic (an agent that increases urine production). Use cautiously in people with an overactive bladder or other urologic disorders and in those taking other diuretic agents. Caffeine may increase voiding, give a sense of urgency, and irritate the bladder.
Although it has not been well studied in humans, caffeine may increase the risk of bleeding. Caution is advised in people with bleeding disorders and in those taking drugs that may increase the risk of bleeding (including warfarin). Dosing adjustments may be necessary.
Caffeine may increase blood sugar levels. Caution is advised in people with diabetes or hypoglycemia and in those taking drugs, herbs, or supplements that affect blood sugar. Blood glucose levels may need to be monitored by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.
Caffeine may increase blood pressure. Caution is advised in people with high blood pressure and in those taking drugs, herbs, or supplements that lower blood pressure (including phenylpropanolamine).
Caffeine may increase blood lipids. Caution is advised in people with elevated blood lipids and in those taking drugs, herbs, or supplements that alter lipid levels.
Caffeine may be associated with seizures. Caution is advised in people with seizure disorders and those taking any drugs to prevent or treat seizures, or when combined with any agents that lower the seizure threshold (including carbamazepine, phenobarbital, phenytoin, valproate, and ethosuximide).
Use cautiously in people with heightened sensitivity to caffeine.
Use cautiously in people with movement disorders or those using drugs that may cause such disorders (e.g., neuroleptics). Caffeine may cause muscle tremors, impair muscle coordination, or provoke disorders that cause uncontrolled movement (e.g., familial paroxysmal nonkinesigenic dyskinesia).
Use cautiously in people with osteoporosis or those at risk for osteoporosis, as caffeine may decrease bone mineral density, promote bone loss, and increase fracture risk.
Use cautiously in people with sleep disorders like insomnia and in those taking other central nervous system (CNS) stimulants, as caffeine may increase these effects and cause insomnia.
Use cautiously in people with glaucoma, as caffeine may increase eye pressure.
Use cautiously in people at risk for kidney stones, as caffeine has been associated with higher urinary calcium, therefore posing an increased risk.
Use cautiously in people with eating disorders, as a high incidence of caffeine consumption may increase the risk of anxiety and mood disorders.
Use cautiously in people who have a weakened immune system and in those using immune system-lowering agents, as caffeine may alter immune function, particularly after exercise.
Use cautiously in people with breast disease, stomach disorders, growth hormone deficiency, or high-grade inflammation; those at risk for kidney or breast cancer; and those who do not consume caffeine regularly (including athletes), due to and increased risk for side effects.
Use cautiously in firefighters wearing protective clothing, as they may be more susceptible to heat-related fatigue and injury.
Use cautiously over prolonged periods of time. Chronic caffeine use may result in increased tolerance and dependence.
Use cautiously in combination with adenosine, agents that affect dopamine, agents that affect the liver's cytochrome P enzyme system (e.g., amitriptyline, ciprofloxacin, clozapine, coconut products, danshen (Salvia miltiorrhiza), disulfiram, echinacea (Echinacea spp.), enoxacin, ethinyl estradiol, flutamide, fluvoxamine, furafylline, genistein, grapefruit juice, imipramine, kudzu (Pueraria lobata), melatonin, methoxsalen, methylxanthines, mexiletine, omeprazole, phenothiazines, and riluzole), agents that depress the central nervous system (e.g., diazepam, midazolam, triazolam, zolpidem, and zopiclone), agents that dilate or constrict blood vessels, agents that mimic the effects of the sympathetic nervous system, antidepressants (e.g., monoamine oxidase inhibitors; MAOIs), antipyrine, calcium, corticosteroids, creatine, fluconazole, geranium (Geranium spp.), iron, lithium, magnesium, and potassium.
Use cautiously in children and the elderly.
Use cautiously for periods greater than four weeks in preterm infants, due to the risk of reduced weight gain and increased oxygen consumption.
Caffeine may pass through breast milk. Use cautiously in amounts greater than three cups of coffee daily in breastfeeding women.
Avoid amounts greater than 200 milligrams daily in pregnant women.
Avoid in people with rosacea (enlarged facial blood vessels).
Avoid in people with Marfan syndrome (a connective tissue disorder), as agents like caffeine that stimulate the cardiovascular system should not be used with this disorder.
Avoid in people with autosomal recessive polycystic kidney disease (a type of genetic kidney disease), as caffeine may promote kidney cyst growth.
Avoid use before adenosine, cardiac, or dipyridamole stress testing, due to potential interference with results.
Avoid use in combination with agents that stimulate the central nervous system, alcohol, and herbs that contain caffeine.
Avoid in those with known allergy or hypersensitivity to caffeine. Elevated heart rate, increased blood pressure, urticaria (skin rash and hives), and allergic lung inflammation have been reported following caffeine and coffee exposure.
