Because sweet fennel fruit has been in use for a long time, the data reviewed by the HMPC included the results of studies from the scientific literature including studies using experimental models.

A relaxing effect on isolated contracted smooth muscles of alcoholic extracts of fennel and fennel essential oil has been reported.
Moreover an anti-inflammatory effect has been reported following oral administration to rats. It was has been observed that a number of compounds detected in fennel fruit inhibit the growth of pathogenic bacteria and fungi. The relaxing and anti inflammatory effects together with the antimicrobial action of their constituents may contribute to the traditional use of sweet fennel medicines in the treatment of minor spasmodic gastro-intestinal complaints and in the treatment of cough associated with colds. Furthermore, the secretolytic and expectorant effect of two main components of sweet fennel fruit (anethole and estragole) observed in a study conducted in rabbits, could also support the plausibility of the traditional use of fennel in cough associated with colds.

There are few studies looking at the safety of sweet fennel fruit preparations, but the many years of experience of their use in man indicate that they are sufficiently safe.

The long-standing use over more than 30 years and limited experimental studies make the traditional use in the above-mentioned indications plausible.