Montanoa tomentosa, commonly known as "zoapatle," has been traditionally used in Mexican folk medicine to address various gynecological conditions, including amenorrhea (the absence of menstruation). Historical records and ethnobotanical studies document its use among indigenous and rural communities, where teas or extracts of the plant are administered to stimulate menstruation, regulate cycles, or even induce labor. The traditional rationale is rooted in observed effects when used in reproductive health, especially among women experiencing delayed or absent periods.

Scientific validation for this specific use, however, remains limited. While some pharmacological studies have investigated the effects of Montanoa tomentosa extracts, most research focuses on its uterotonic properties—its ability to stimulate uterine contractions—in animal models. These effects could theoretically support its use in cases of amenorrhea, especially if the underlying cause involves insufficient uterine activity. Some studies suggest the presence of active phytochemicals such as sesquiterpene lactones, which may impact reproductive physiology. However, robust clinical trials in humans are lacking, and the precise mechanisms remain unclear.

In summary, the use of Montanoa tomentosa for amenorrhea is primarily justified by traditional practices, with some preliminary scientific findings supporting its potential to influence uterine activity. The overall evidence base is modest, with most support derived from ethnobotanical sources rather than rigorous clinical research.