Why You Should Avoid Taking Pueraria Mirifica — Despite Its Natural Health Claims

Many people in Thailand consider Pueraria mirifica a virtual fountain of youth. In fact, the roots of this native Thai plant contain at least 17 phytoestrogens, chemicals that exert effects in the body similar to naturally occurring estrogen, a March 2012 Frontiers of Medicine study found.

Thai healthcare practitioners prescribe Pueraria mirifica as a rejuvenating therapy for older people and to treat of an array of medical conditions, including heart disease, stroke, endometriosis and diabetes. Manufacturers also market it as an alternative to hormone replacement therapy for the relief of menopausal symptoms and to promote breast enlargement.

Read more: Which Foods Are High in Natural Estrogen?

Although Pueraria mirifica has been used for many years in Southeast Asia, high quality human research evaluating its safety and effectiveness is lacking. Information about potentially dangerous side effects of Pueraria mirifica derive primarily from laboratory and animal studies.

Phytoestrogens like those in Pueraria mirifica exert their effects in two ways. The chemicals bind to estrogen receptors on cell surfaces, which triggers specific activities within the cells. They also influence the activity of enzymes involved in the production and breakdown of naturally occurring estrogen, thereby affecting the level of the hormone in various body tissues. Via these mechanisms of action, phytoestrogens have the potential to disrupt a woman's menstrual cycle.

Two seminal studies conducted in the early 2000s found that administration of Pueraria mirifica disrupted the menstrual cycles of monkeys, as reported in the January 2004 issue of the Journal of Pharmacological Sciences and the February 2005 issue of the journal Endocrine. In the study reported in Endocrine, menstrual cycles stopped completely in monkeys treated with the highest dose of Pueraria mirifica. These studies continue to be relevant and are frequently cited in the medical literature as evidence of concern for hormonal disruption in people taking Pueraria mirifica.

Soybeans and soy products contain some of the same phytochemicals found in Pueraria mirifica. The July/August 2009 issue of Human Reproduction Update included an analysis of the combined results from 47 studies that examined the effects of soy and soy-derived phytoestrogens on women's reproductive hormone levels and menstrual cycles. The analysis remains the most comprehensive to date on this topic. Among women who had not yet reached menopause, soy and/or soy phytoestrogen consumption was associated with an increase in menstrual cycle length and reduced levels of follicle-stimulating hormone and luteinizing hormone, which play crucial roles in menstrual cycle regulation and ovulation. Although this study assessed the effects of soy phytoestrogens, the findings are consistent with the monkey studies evaluating the effects of Pueraria mirifica.

Read more: Is Eating Soy Actually Bad for Your Health?

Use of phytoestrogens, including those found in Pueraria mirifica, raises a concern about a potentially increased risk for hormone-sensitive cancers, including breast, ovarian and endometrial cancer. As of 2019, no long-term human studies evaluating use of Pueraria mirifica and the risk of these or other cancers have been been conducted. However, a study reported in the March 2012 issue of the journal Toxicological Sciences found that exposure to a phytoestrogen mixture containing two of most abundant phytoestrogens in Pueraria mirifica promoted the development of mammary and endometrial cancers in rats. Mammmary cancer in rats is akin to human breast cancer.

A phytoestrogen called genistein is abundant in both Pueraria mirifica and soybeans. This substance binds to and activates a particular estrogen receptor called GPER. GPER is commonly expressed in a broad range of cancer cell types, including those of the endometrium, ovary, breast, thyroid, lung, prostate and testicle. In the laboratory, stimulation of GPER by genistein promotes proliferation of these cancer cells, according to a July 2015 review published in Pharmacological Reviews.

Read more: 10 Foods That Might Increase Your Cancer Risk

There is no evidence proving Pueraria mirifica increases human cancer risk. Laboratory and animal research findings, however, point to the importance of conducting long-term, well-designed research to address this important issue.

As with any drug, treatment with medicinal estrogen carries certain health risks. It is currently unknown whether the phytoestrogens in Pueraria mirifica pose health risks similar to medicinal estrogen. According to the Prescribers' Digital Reference, these include but are not limited to:

• Increased dementia risk in those older than 65 years
• Worsening incontinence
• New or worsening gallbladder disease
• Inflammation of the pancreas (pancreatitis)
• Blood clots
• Fluid retention
• New or worsening high blood pressure
• High blood sugar
• Headaches
• Weight gain
• Breast tenderness
• Breakthrough bleeding between periods
• Irritability

Because it remains unknown whether Pueraria mirifica poses risks similar to medicinal estrogen, be sure to talk with your doctor before starting this supplement if you have an estrogen-sensitive medical condition, such as:

• Endometriosis
• Uterine fibroids
• Liver disease or liver cancer
• Gallbladder disease
• Pancreatitis
• Systemic lupus erythematosus
• Hypothyroidism
• Asthma
• Heart disease
• Depression
• Previous stroke, deep venous thrombosis or phlebitis