About Fennel
Fennel (Foeniculum vulgare) seed contains trans-anethole (~70% of essential oil), fenchone, and estragole. Trans-anethole has phytoestrogenic activity, which underlies most clinical effects. Best-supported indications: infant colic (multiple small RCTs of fennel seed emulsion showed reduced crying time vs. placebo — a 2003 Alexandrovich RCT and subsequent trials), primary dysmenorrhea (several small RCTs vs. mefenamic acid showed comparable pain reduction), and post-menopausal vasomotor symptoms (small RCTs showed reduction in hot flashes). Also traditional digestive aid for bloating and flatulence — physiologically plausible but few RCTs. SAFETY: estragole is genotoxic and hepatocarcinogenic in rodents at high doses; EMA limits long-term continuous fennel use to 2 weeks for this reason. Phytoestrogenic — avoid in hormone-sensitive conditions (estrogen-receptor-positive breast cancer, endometriosis). Cross-reactive allergy with celery/carrot/parsley.
What Fennel supports
- Reduces infant colic crying time in small RCTs
- Reduces primary dysmenorrhea pain comparable to mefenamic acid in small RCTs
- Phytoestrogenic; EMA caps continuous use at 2 weeks due to estragole genotoxicity
How much Fennel to take
The RDA prevents deficiency. The effective range is what clinical trials used to actually move the outcome.
Effective
500–1500
mg
Whole-seed traditional dose is 1.5–3 g/day; standardized extracts cluster at 300–600 mg. Dysmenorrhea RCTs typically used 30–60 mg fennel extract every 4 hours during menstruation.
Clinical evidence
Moderate clinical evidence. Multiple small RCTs support infant colic, dysmenorrhea, and vasomotor symptoms; long-term safety capped by estragole genotoxicity concerns.
Reference