Benefits
Company-reported placebo-controlled study in 167 women (unpublished)
Nexira says it tested BloomEase at 520 mg once daily against placebo in 167 women over four menstrual cycles and reports less period pain from the first cycle, better mood and sleep, and better quality of life. The study has not been published in a peer-reviewed journal, so its design, blinding, results and statistics cannot be checked outside the company.
Marketed for both phases, but the published yarrow trial tested period pain only
The product is marketed for the days before a period and for the period itself. The one placebo-controlled yarrow trial measured period pain only, not mood, bloating or other symptoms before bleeding. The premenstrual evidence on this page comes from small trials of ordinary magnesium, not from yarrow or BloomEase. Nexira says its unpublished study covers both phases, which cannot yet be checked.
Ordinary magnesium and premenstrual symptoms in placebo-controlled trials
In a double-blind trial in 32 women, oral magnesium in the second half of each cycle improved total premenstrual symptom and negative mood scores versus placebo. In two crossover trials of 200 mg a day, magnesium alone did not beat placebo over one cycle; one found less fluid retention in the second cycle. All used ordinary magnesium, not marine magnesium or BloomEase.
Menstrual pain scores in a placebo-controlled yarrow tea trial
In a double-blind trial in 96 female university students with painful periods and no underlying cause, yarrow tea with each meal for 3 days in each of two cycles lowered pain scores more than a starch placebo. It used about 12 g of herb a day, which EU assessors called well above their guidance, and tested yarrow alone; BloomEase's yarrow content is not public.
Mechanism of action
Magnesium, calcium movement and muscle contraction
Magnesium is a cofactor in more than 300 enzyme systems and helps move calcium and potassium across cell membranes, a process involved in nerve signaling and muscle contraction. That is the proposed reason magnesium might ease cramping, but the trials cited here did not measure uterine muscle activity.
Magnesium and anxiety-related symptoms
Magnesium status has been linked with anxiety, which led researchers to test supplements for anxiety-related symptoms. A systematic review found that four of seven premenstrual studies reported less anxiety and three did not, and its authors rated the quality of the evidence as poor.
Yarrow flavonoids relax gut muscle in lab tests
On isolated guinea-pig intestine, a yarrow flavonoid fraction had antispasmodic activity, and among single flavonoids quercetin, luteolin and apigenin were the most active, acting mainly by blocking calcium entry into muscle cells; rutin had no significant effect. This is the proposed basis for the traditional use for cramps; it was not tested on uterine muscle or in people.
Yarrow's sesquiterpene lactones and skin allergy
Yarrow contains sesquiterpene lactones; the main one, alpha-peroxyachifolid, was a strong sensitizer in guinea pigs, and EU assessors report that more than half of patients already sensitive to daisy-family plants reacted to a yarrow extract on patch testing. This is an allergy mechanism, not a muscle-relaxing one.
Clinical trials
Described by Nexira as a real-life, placebo-controlled study of BloomEase at 520 mg once daily over four menstrual cycles. The yarrow and magnesium amounts, protocol, randomization, blinding, dropouts and statistics have not been released, and no peer-reviewed paper exists. Run and reported by the maker. (Lannebere 2026, Nexira company website)
167 women (company description; inclusion criteria and ages not published).
Not peer reviewed. Nexira reports up to 32% better menstrual comfort than placebo from the first cycle, fewer women with intense period pain after three cycles, better mood and sleep, and up to 52% better personal and professional quality of life after two cycles. None of these figures can be checked independently.