Objective Fennel seed oil has been shown to reduce infantile spasm. Chemical drugs have different side effects so we surveyed the effect of fennel essence and gripe water syrup in infantile colic.

Methods This randomised clinical trial of 81 infants up to 4 months of age in Arak, Iran, assessed the comparative effect of fennel essence (1% concentration, one teaspoon for newborns, one table spoon for 1–6-month-old infants, three times a day, for one week) with gripe water syrup in infantile colic (dosage as case group). Before intervention the mean duration of crying was determined then divided into three times: less than 60, 60–12 and more than 120 minutes, on the 3rd and 7th day after treatment these times were compared with before. Data were analysed with the χ² test.

Results Before intervention the mean duration of crying in the fennel group was: 56/1% less than 60, 36/6% between 60 and 120 and 7/3% more than 120 minutes and in the gripe water group: 63/4% less than 60, 29/3% between 60 and 120, 7/3% more than 120 minutes. The difference between the two group was not statistically significant. After treatment on the 3rd and 7th day these times compared with before, in the fennel group the difference was statistically significant (p = 0.004, 0.05), and also in the gripe water group (p = 0.037, 0.002), no infant cried for more than 2 h in the two groups. The difference was insignificant between the two groups after treatment.

Conclusion Essence of fennel is as effective as gripe water syrup in the relief of infantile colic, so it can be used as a safe, effective and cost-effective herbal drug for infantile colic.