Guarana, with the main chemical component caffeine, is promoted as a stimulant herb, an appetite suppressant and an aphrodisiac. White willow bark is primarily used to relieve pain, as it contains salicin, a chemical that was used to develop aspirin. Combining the two herbs may increase the risk of some negative effects associated with them. Consult a qualified health care provider before taking guarana or white willow bark.
Caffeine Side Effects
Most side effects associated with guarana are due to its caffeine content, according to eMedTV. Particularly if you are not accustomed to caffeine, you may experience jittery feelings, nervousness, restlessness and insomnia. Other caffeine-related side effects may include increased urination and headaches. Both caffeine and white willow bark can cause ringing in the ears, so taking the two together may worsen this effect. More serious side effects associated with high caffeine intake include anxiety, confusion, dizziness, a rapid or irregular heart rate, and heart palpitations.
Gastrointestinal Effects
Caffeine also can cause heartburn, upset stomach and nausea. Stomach irritation and nausea are possible adverse effects of white willow bark as well. Like other nonsteroidal anti-inflammatory drugs such as aspirin, ibuprofen and naproxen, white willow bark can lead to gastrointestinal ulcers and stomach bleeding in some people. Taking willow in addition to any of these medications may increase the risk of stomach bleeding, according to the University of Maryland Medical Center.
Anticoagulant Effects
White willow bark and guarana both have anticoagulant effects, according to the Memorial Sloan-Kettering Cancer Center. Taken separately or together, they can boost the effects of drugs and herbs with blood-thinning activity. This increases the risk of bleeding. Some medications with blood-thinning effects include warfarin, heparin, ibuprofen and aspirin. Some other herbs with this activity include ginkgo, garlic and ginger.
Hypertension
Infrequently, caffeine has been linked to high blood pressure. In addition, white willow bark may reduce the effectiveness of beta blockers used to regulate blood pressure, according to UMMC. Combining guarana and white willow bark may be especially problematic for people who already have high blood pressure and take beta blockers such as atenolol, metoprolol or propranolol.
Allergic Reactions
Both guarana and white willow bark can cause allergic reactions. Do not take white willow bark if you are allergic or sensitive to aspirin or other salicylates, cautions UMMC. Signs of an allergic reaction to herbal remedies may include itching, a rash, hives, wheezing or trouble breathing, unexplained swelling or difficulty swallowing. An allergic reaction to either guarana or white willow bark calls for immediate medical attention.
Reye's Syndrome
Children under age 16 should not take willow bark because it may lead to Reye's syndrome, according to UMMC. This rare and serious illness is connected to aspirin usage in youngsters, particularly those recovering from a viral infection. Reye's syndrome causes swelling in the liver and brain.
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