The ancient Greek, Chinese, Indian and Egyptian civilizations all used fennel for food and medicine. Traditional uses ranged from expelling gas to infant colic, but whether it actually works for any purpose remains unclear due to a lack of human studies. Its long history of use as a food suggests it does not pose any significant health risks but like any supplement, it has the potential to cause adverse effects. Talk to your doctor before using fennel supplements.
Fennel Seed vs. Fennel Oil
People using fennel medicinally typically consume the crushed seeds or use the seeds to make a tea. Do not use fennel oil. Certified lactation consultant Kelly Bonyata, explains fennel oil in even small quantities -- a teaspoon or less -- can cause serious problems such as seizures and respiratory distress. Drugs.com notes studies that found a component of fennel oil stimulated tumor growth in animals.
Side Effects
Fennel seed might cause rash and photodermatitis, a skin reaction triggered by increased sensitivity to sunlight.
Medication Interactions
Animal research suggests fennel seed might interfere with the absorption of antibiotics in the ciproflaxin family, according to the University of Pittsburgh Medical Center. It notes taking the supplement and the medications at least two hours apart might prevent this effect but perhaps not fully. It is prudent to hold off on using fennel seeds during your course of therapy.
Considerations for Pregnant and Nursing Women
Traditionally, fennel was used to stimulate menstruation and Drugs.com reported documented adverse reactions when used in pregnancy. For these reasons, do not use it while pregnant. Bonyata explains fennel helps stimulate milk production, but using too much might actually decrease it. She recommends a dose of 2 to 4 mL of tincture two to three times a day or 1 ½ to 2 tsp. of seed in 1 cup of hot water, two to three times a day. Always discuss the use of supplements with your doctor while breastfeeding.
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