Benefits
Traditional European herbal use around menstruation
An EU herbal monograph accepts the herb tea and a 1:1 liquid extract as a traditional herbal medicine for reducing heavy menstrual bleeding in adult women with regular cycles, after a doctor has excluded serious causes. This rests on at least 30 years of documented use; the assessors found no clinical trials and no studies on blood clotting.
Menstrual blood loss in clinical trials
Small Iranian trials have scored menstrual blood loss with a picture chart. In the only trial against placebo alone, in women with fibroids, 3 months of extract did not differ from placebo. In another, extract or placebo was added to the painkiller mefenamic acid; the authors reported a larger drop with the extract, but an EU review found no significant group difference in monthly scores.
Uterine muscle and inflammation findings in lab and animal work
Lab and animal work only: extracts made isolated rat, rabbit and guinea pig uterine tissue contract, and a shepherd's purse polyphenol extract given by mouth reduced experimental paw swelling in mice. EU assessors noted that most of the older studies give few details and that none tested an effect on bleeding. None of this has been shown in people.
Mechanism of action
Uterine smooth muscle contraction in lab tests
Water and alcohol extracts made isolated uterine tissue from rats, rabbits and guinea pigs contract. One purified fraction acted like a small dose of oxytocin on rat uterus and appeared to be a polypeptide. Researchers concluded the effect was not due to the acetylcholine or histamine the plant contains. These are lab findings, not shown in people.
Anti-inflammatory and antioxidant activity in cells and mice
A polyphenol-rich extract lowered inflammatory signals (TNF-alpha, IL-6, nitric oxide) in mouse immune cells and, at 400 mg/kg by mouth, reduced carrageenan paw swelling in mice. Two of eight isolated phenolic glycosides moderately reduced nitric oxide in mouse brain immune cells. Cell and animal work only.
No proven effect on blood clotting
Despite its folk reputation as a styptic, EU assessors found no studies of a hemostatic (clot-promoting) action. The plant contains vitamin K and flavonoids that reduced blood vessel leakiness in animal tests, but how, or whether, the herb affects bleeding in people is unknown.
Clinical trials
Triple-blind randomized trial at gynecology clinics of Shahid Beheshti University, Tehran, of hydroalcoholic shepherd's purse extract capsules or placebo, each given with mefenamic acid, from the first day of the period for up to 7 days over two cycles. (Naafe et al. 2018, J Altern Complement Med)
84 women with heavy menstrual bleeding confirmed by a pictorial blood loss assessment chart (42 per group); an EU review of the paper describes 100 women. Per that review, each capsule held 320 mg of extract, two capsules every 12 hours.
Bleeding fell in both groups. The authors report a significantly larger mean decrease with the extract (p < 0.001). An EU (HMPC) review of the same paper reported no significant difference between groups in chart scores in the first (p = 0.678) or second month (p = 0.242), a higher reduction rate with the extract (p = 0.032), and no between-group difference in bleeding days at the end. Per that review, the alcohol strength and drug-to-extract ratio of the extract were not reported.
Double-blind randomized placebo-controlled trial in gynecology outpatient clinics in Iran of alcoholic shepherd's purse extract for menstrual blood loss and quality of life; not indexed in PubMed. (Sadat Danesh et al. 2019, J Pharm Res Int)
54 women with uterine leiomyoma (fibroids) and heavy menstrual bleeding, given 350 mg of extract or placebo twice daily for 3 months.
Mean blood-loss chart scores fell from 464.00 to 323.82 with the extract and from 445.92 to 214.36 with placebo by the third month; both groups improved, with no significant difference between them. Bleeding duration and menstrual quality of life also improved in both groups without a between-group difference. A null result versus placebo.
Triple-blind randomized trial in 2022 at health centers of Kermanshah University of Medical Sciences, Iran, comparing shepherd's purse extract capsules with mefenamic acid; no placebo group; not indexed in PubMed. (Ahmadipoor et al. 2023, Iran J Obstet Gynecol Infertil)
80 girls with primary dysmenorrhea (40 per group): capsules of 400 mg hydroalcoholic extract, or mefenamic acid 250 mg capsules, both every 8 hours from the first day of the period for up to 3 days, in each of two consecutive periods (per the Persian abstract; the English abstract is less clear).
Baseline pain was similar (p = 0.689). Visual analog pain scores differed between groups over time (p = 0.001), with a larger fall in the herb group. The abstract reports no group means, effect sizes or side effect data. Without a placebo arm, the trial shows only how the two compared in this small group.
Single-blind randomized trial at Afzalipour Hospital, Kerman, Iran, in 2015 of sublingual shepherd's purse extract drops or placebo drops, each given with an oxytocin infusion right after delivery of the placenta. (Ghalandari et al. 2017, J Altern Complement Med)
100 women who had given vaginal birth (50 per group); 10 drops of hydroalcoholic extract (50 mg of extract per drop, per an EU review) or 10 placebo drops, plus 20 units of oxytocin in 1 liter of Ringer's solution.
Measured bleeding decreased in both groups, and the mean decrease was significantly larger with the extract (p < 0.001); hemoglobin and hematocrit were checked 6 hours after birth. The EU (HMPC) review judged the trial not relevant for its monograph because the extract's solvent strength and ratio were not reported. A one-time hospital use alongside a drug, not self-care.