Bidens pilosa L. is an Asteraceae growing in tropical zones, and traditionally utilized worldwide in
herbal medicine. The present work is based on its traditional use during child birth as a labour facilitator. In vivo
tests of acute toxicity showed a weak toxic effect for both extracts but the toxicity of the ethanol extract
(LD50=6.15g/kg) was upper than that of the aqueous extract (LD50=12.30g/kg). The three-days uterotrophic
assay on immature mice showed body weight gain followed by a concentration-dependent decrease up to 4mg/g
and a concentration dependent uterine wet weight increase. The ethanol extract exhibited the higher body weight
gain representing 22.8±0.7%, (P≤0.001), at the concentration of 500µg/g/day, while the aqueous extract was
significantly more efficient on the uterine wet weight gain of 0.24±0.001% (P≤0.05), at the concentration of
1000µg/g/day. In vitro isometric contraction measurement of oestrogen-primed rat uterine strips showed a
significant high aqueous extract-induced contractile effect from 0.03-1.97mg/ml: on the amplitude of
contraction (EC50 = 0.44±0.10mg/ml, P≤0.05), and on the rate (1.21±0.25mg/ml, P>0.05). Inspite of the higher
effect of the aqueous extract on the tonus (57.23±23%), the ethanol extract showed a high effect (EC50=
0.34±0.09mg/ml, P≤0.05). The weak toxicity, the estrogenic-like and the oxytocic-like activities observed could
explain the empirical use of Bidens pilosa leaf aqueous extract as an uterotonic preparation to enhance labour,
probably due to the presence of biologically active compound(s) which act directly on the uterine muscle.