Possible side effects of guarana include insomnia, nervousness, restlessness, stomach irritation, nausea, vomiting and frequent urination. Guarana contains the stimulant caffeine, and because of this, has the potential to cause symptoms like headaches, anxiety, ringing in your ears, painful urination, stomach cramps and heart palpitations.
After taking guarana regularly for a period of weeks or months, you may experience symptoms of caffeine withdrawal if you suddenly discontinue using the supplement. Caffeine withdrawal symptoms include headaches, anxiousness, sluggishness and depression, explains the University of Wisconsin at Stevens Point.
When combined with amphetamine medications like phentermine or the weight loss medication ephedrine, guarana poses a risk for severe increases in blood pressure or heart rate, warns RxList. Drugs like the quinolone antibiotic ciprofloxacin, the GERD medication cimetidine, the addiction drug disulfiram, estrogen supplements, the antidepresants fluvoxamine and MAOI inhibitors increase your risk of experiencing side effects from guarana.
Serious health risks associated with use of guarana include increased heart rate, hypertension, tremors and delirium, warns RxList.
If you are pregnant or nursing, consult your doctor before using guarana. If you have a history of heart disease, hypertension, anxiety, bleeding disorders, glaucoma or osteoporosis, it may not be safe for you to take guarana, warns RxList.