Therapeutic effect of Vitex agnus castus in patients with premenstrual syndrome 

This randomized, placebo controlled double blind study from 2012, provided patients with 40 drops of vitex preparations or placebo for six days preceding menstruation for six consecutive cycles. This study is unique in design in that it only provided treatment in the luteal phase preceding menses and was conducted for a longer period than any other study (i.e. six months and had a screening period of two cycles for all participants to properly establish a baseline of symptoms). Of the 128 participants recruited, 62 were active while 66 were assigned to the placebo group. The authors conclude that this is a well-tolerated option for the management of mild to moderate PMS symptoms.   

References:

Zamani M, Neghab N, Torabian S. Therapeutic effect of Vitex agnus castus in patients with premenstrual syndrome. Acta Med Iran. 2012;50(2):101–106. https://pubmed.ncbi.nlm.nih.gov/22359078/