Biest is a compounded hormone cream or gel that combines two forms of estrogen, estriol and estradiol, typically in an 80:20 ratio by weight. It is one of the most commonly prescribed formulations in the world of compounded bioidentical hormone therapy, used primarily by women looking to manage menopausal symptoms like hot flashes, night sweats, and vaginal dryness. Despite its popularity, biest occupies an unusual space in medicine: it is not FDA-approved as a finished product, the ratio of its ingredients is based more on tradition than clinical trials, and major medical societies have recommended against it when FDA-approved alternatives are available.
What the Formula Actually Contains
The “bi” in biest refers to two estrogens. Estradiol is the most potent estrogen the body produces and is the form used in virtually all FDA-approved estrogen therapies, from patches to pills. Estriol is a weaker estrogen, produced in large quantities during pregnancy but present at much lower levels in non-pregnant women. In the standard biest formulation, estriol makes up 80% and estradiol makes up 20%. So a 2.5 mg dose of biest delivers 2.0 mg of estriol and 0.5 mg of estradiol. A randomized clinical trial of postmenopausal women tested compounded biest cream at doses of 2.0, 2.5, and 3.0 mg, all at the 80:20 ratio, paired with 100 mg of compounded oral progesterone.1PubMed. Bioidentical compounded hormones: a pharmacokinetic evaluation in a randomized clinical trial
The rationale behind loading the formula with estriol is the belief that estriol is a “weaker” and therefore “safer” estrogen, providing symptom relief without the risks associated with stronger estrogens. This idea has been a cornerstone of compounding pharmacy marketing for years, but the evidence behind that specific 80:20 split is thin. No large trial has ever demonstrated that this particular ratio is superior to other combinations or to estradiol alone. The ratio appears to have originated from clinical tradition among compounding practitioners rather than from dose-finding studies.
How Estriol and Estradiol Behave Differently in the Body
Estradiol and estriol are both natural human estrogens, but they interact with the body’s estrogen receptors in meaningfully different ways. The body has two main types of estrogen receptors, commonly called alpha and beta. Estradiol binds to both with roughly equal and strong affinity. Estriol, by contrast, binds more weakly overall but shows a preference for the beta receptor, with up to an 18-fold selectivity for beta over alpha in binding studies.2Endocrinology. Quantitative Structure-Activity Relationship of Various Endogenous Estrogen Metabolites for Human Estrogen Receptor α and β Subtypes In the same research, estradiol showed nearly equal binding to both receptor subtypes, while estrone, another common estrogen, preferred the alpha receptor.
This distinction matters because the two receptor types are distributed differently across tissues. Alpha receptors are concentrated in the uterus, breast, and liver, while beta receptors are more abundant in bone, the brain, the cardiovascular system, and the urinary tract. The theory behind biest is that estriol’s preference for beta receptors might provide benefits to those tissues while putting less estrogenic stimulation on breast and uterine tissue. Earlier receptor studies confirmed the general pattern: estriol competes less strongly than estradiol for binding at both receptor types, sitting well below estradiol in the binding hierarchy.3PubMed. Comparison of the ligand binding specificity and transcript tissue distribution of estrogen receptors alpha and beta
The catch is that receptor binding affinity in a lab dish does not translate directly into clinical safety. A weaker estrogen given at a higher dose can still produce strong estrogenic effects. And in the standard biest formula, estriol is delivered at four times the dose of estradiol, which partly compensates for its weaker binding. Whether this selective receptor profile produces genuinely different safety outcomes has not been settled by the kind of large, long-term trials that would be needed.
How Biest Gets Through the Skin
Most biest is applied as a topical cream, usually to the inner arm, wrist, or thigh. The hormones absorb through the skin and enter the bloodstream, bypassing the liver on their first pass through the body. This transdermal route is a deliberate choice: oral estrogens pass through the liver first, which triggers changes in clotting factors and inflammatory markers that transdermal delivery largely avoids.
Skin permeation studies using excised human skin have measured how much estradiol and estriol actually cross when formulated together in a biest cream. In one study, when the two hormones were compounded together, their individual permeation rates dropped to roughly one-quarter of what each achieved alone. Despite this interaction effect, the estimated daily delivery from a standard application was about 0.5 mg of estradiol and 2.0 mg of estriol, which researchers considered sufficient for systemic activity.4PubMed. Evaluation of percutaneous absorption performance for human female sexual steroids into pentravan cream
That four-fold reduction in permeation when the estrogens are combined is worth knowing, because it means the actual dose reaching your bloodstream from a biest cream can be substantially different from what the label suggests. This is one reason that hormone levels measured through blood tests after using biest can be unpredictable, and why prescribers who work with compounded hormones often adjust doses based on follow-up lab work rather than relying on a fixed prescription.
What the Evidence Says About Symptom Relief
The clinical trial data on biest specifically, as opposed to estradiol or estriol used individually, is limited. Most of the large hormone therapy trials that have shaped medical guidelines used FDA-approved estradiol products, not compounded biest. The studies that do exist on compounded bioidentical formulations tend to be small, observational, or short-term.
One observational study of women receiving compounded bioidentical hormone therapy, including biest formulations, found reductions in night sweats and hot flashes within three to six months. Night sweats dropped by about 14 percentage points and hot flashes by about 6 percentage points, but neither change reached statistical significance.5PubMed Central. Effectiveness of Compounded Bioidentical Hormone Replacement Therapy: An Observational Cohort Study That does not mean biest has no effect on symptoms. It means the study was not large or controlled enough to prove one. Many women report dramatic relief, but clinical science needs more than individual reports to draw firm conclusions.
A separate study tracked women on compounded transdermal bioidentical hormones and found favorable changes across a range of measures, including menopause symptom scores, anxiety and depression scales, fasting glucose, triglycerides, and several inflammatory and clotting markers.6PubMed. The effects of compounded bioidentical transdermal hormone therapy on hemostatic, inflammatory, immune factors; cardiovascular biomarkers; quality-of-life measures; and health outcomes in perimenopausal and postmenopausal women These are encouraging signals, but the study lacked a placebo control group, which makes it impossible to know how much of the improvement came from the hormones versus other factors.
The frustrating reality is that biest has been used by thousands of women for decades, yet the kind of rigorous, randomized, placebo-controlled trials that would definitively establish its effectiveness have never been done. Compounding pharmacies, which make biest to order for individual patients, do not have the same incentive or regulatory pathway to fund large clinical trials the way pharmaceutical companies do for patented products.
The Transdermal Advantage and Cardiovascular Considerations
One of the strongest arguments in biest’s favor has less to do with its specific formula and more to do with how it is delivered. Transdermal estrogen, whether it comes from an FDA-approved patch or a compounded biest cream, avoids the liver’s first-pass metabolism. Oral estrogen passes through the liver before entering general circulation, and this triggers increased production of clotting factors, C-reactive protein, and other inflammatory markers.7PubMed. Are all estrogens created equal? A review of oral vs. transdermal therapy
Large trials over the past fifteen years have shown an increased risk of blood clots in women using oral, mostly non-bioidentical hormone therapy. A review of the evidence concluded that the risk of vascular complications depends on the route of administration, the age of the user, the duration of treatment, and whether the hormones are bioidentical. Based on this, the authors suggested that bioidentical hormone therapy given through the skin appears to be the safest approach, though they acknowledged that large-scale trials specifically for bioidentical hormones are still needed.8PubMed Central. Prevention and treatment of venous thromboembolism during HRT: current perspectives
This is where the conversation gets nuanced. The cardiovascular safety advantage of transdermal delivery is real and well-supported, but that advantage belongs to transdermal estrogen in general, not to biest in particular. An FDA-approved estradiol patch delivers estrogen transdermally too, and has the clinical trial data to back its safety profile. Biest’s advocates sometimes conflate the benefits of transdermal delivery with the benefits of the biest formula itself, and those are separate questions.
Are All Estrogens Really the Same?
A key question behind the entire biest concept is whether different estrogens carry different risks. The marketing around compounded bioidentical hormones often implies that estriol is fundamentally safer than estradiol or synthetic estrogens like conjugated equine estrogens. A review examining this question concluded that no convincing evidence shows the various estrogens differ in their effects in any qualitative way. The differences that do exist are quantitative, driven by differences in receptor affinity, how quickly the body breaks them down, and the route of delivery.9Maturitas. Are all estrogens the same?
In practical terms, this means estriol is not a categorically different drug from estradiol. It is a weaker version of the same thing. At sufficient doses, estriol stimulates the same pathways estradiol does, including stimulating the uterine lining. The idea that estriol provides a kind of “gentle” estrogen effect that avoids risks is appealing but has not been proven in the way it would need to be. This does not mean biest is dangerous; it means the safety claims made on its behalf have outrun the evidence.
What Medical Societies and the FDA Say
The major medical organizations that issue guidelines on menopause treatment have taken a consistent position: compounded bioidentical hormone therapy, including biest, should not be used by women who can take FDA-approved hormone therapy. The Endocrine Society, the North American Menopause Society, the American College of Obstetricians and Gynecologists, the American Society for Reproductive Medicine, and the International Menopause Society have all recommended against compounded bioidentical hormones except in cases where a medical condition prevents a woman from using an approved product.10PubMed Central. Update on medical and regulatory issues pertaining to compounded and FDA-approved drugs, including hormone therapy
Their reasoning centers on a few concerns. First, compounded products do not go through the FDA approval process, which means they have not been tested in controlled trials for safety and effectiveness the way approved drugs have. Second, quality control at compounding pharmacies is variable. Unlike pharmaceutical manufacturers, compounding pharmacies are not required to demonstrate batch-to-batch consistency to the FDA, and independent testing has found that some compounded hormone preparations contain doses that differ from what is on the label. Third, there is no requirement for a package insert listing risks, which means patients may not receive the same safety information they would get with an FDA-approved product.
A review article highlighted additional concerns, noting case reports of endometrial cancer in otherwise healthy women using compounded bioidentical hormones, and concluded that the lack of sufficient data to support either the efficacy or safety of compounded bioidentical therapy favored recommending FDA-approved regimens instead.11Journal of Women’s Health. Risks and effectiveness of compounded bioidentical hormone therapy: a case series A separate review echoed this, noting that compounded bioidentical formulations lack well-controlled studies examining their pharmacokinetics, safety, and the scientific rationale for the mixture ratios commonly used.12Journal of Women’s Health. Bioidentical hormone therapy: a review of the evidence
Why Women Choose Biest Anyway
Given the skepticism from mainstream medical organizations, it is worth understanding why so many women seek out compounded biest in the first place. A qualitative study exploring the decision-making process of women who chose compounded bioidentical hormones found that motivations fell into two broad categories. “Push” factors drove women away from conventional hormone therapy or from alternatives like herbal supplements that were not working. “Pull” factors drew them specifically toward compounded options.13PubMed Central. Why women choose compounded bioidentical hormone therapy: lessons from a qualitative study of menopausal decision-making
The push factors often included fear of breast cancer or blood clots after news coverage of the Women’s Health Initiative trial in 2002, dissatisfaction with how conventional doctors handled their menopausal symptoms, and side effects from FDA-approved hormone products. The pull factors included the perception that “natural” or “bioidentical” hormones are inherently safer, the appeal of individualized dosing tailored to their specific hormone levels, and positive word-of-mouth from other women. After the WHI findings made headlines, interest in compounded bioidentical hormones surged as women looked for alternatives they perceived as less risky.14PubMed Central. Bioidentical hormone therapy
These are legitimate concerns. The WHI results did show real risks, and many women had genuinely bad experiences with conventional hormone therapy. The problem is that the alternative they turned to has even less safety data, not more. The word “bioidentical” implies a meaningful distinction, but the estradiol in an FDA-approved patch is chemically identical to the estradiol in a compounded biest cream. Both are bioidentical. The difference is that one has been tested in large trials and the other has not.
Topical Estrogens and Skin
One area where both estradiol and estriol have shown measurable effects outside of menopausal symptom relief is skin health. A six-month trial in which postmenopausal women applied either topical estradiol or topical estriol to their facial skin found that both treatments produced marked improvements. Skin elasticity and firmness improved, while wrinkle depth and pore size decreased by 61 to 100 percent depending on the measure. Skin moisture increased, and biopsy samples showed significant increases in type III collagen fibers.15PubMed. Treatment of skin aging with topical estrogens
These findings are relevant to biest users because they suggest that the estriol component, not just the estradiol, has biological activity when applied to the skin. This is sometimes cited as evidence that estriol “does something,” which it clearly does. The question has never been whether estriol is biologically active. It is. The question is whether the specific 80:20 combination in biest produces a different risk-benefit profile than estradiol alone, and skin studies cannot answer that.
Some compounding pharmacies market biest-containing facial creams specifically for anti-aging purposes, leaning on studies like this one. These products exist in a regulatory gray area, since topical estrogens applied for cosmetic purposes can still be absorbed systemically and can affect hormone-sensitive tissues elsewhere in the body. If you are using a biest cream on your face for wrinkles, you are still taking a hormone, and the systemic effects should be discussed with your prescriber.
Practical Considerations If You Are Using or Considering Biest
If your provider has recommended biest or you are thinking about requesting it, a few things are worth keeping in mind. First, ask whether the specific benefit you are hoping for could be achieved with an FDA-approved transdermal estradiol product. These deliver bioidentical estradiol through the skin and come with established dosing guidance, safety data, and quality guarantees. If the main appeal is avoiding oral hormones, a patch or gel accomplishes that without the uncertainties of compounding.
Second, if you do use compounded biest, make sure your prescriber monitors your hormone levels with blood or saliva tests and adjusts the dose based on results, not just symptoms. The variability in skin absorption and compounding consistency means the dose that reaches your bloodstream can differ from what is written on the prescription.
Third, understand that “bioidentical” does not mean “risk-free.” Estradiol, whether compounded or FDA-approved, carries risks for blood clots, stroke, and hormone-sensitive cancers, particularly when used for long periods at higher doses. Estriol’s weaker potency does not automatically exempt it from these risks when given at the doses typical of biest. Progesterone should be co-prescribed if you have a uterus, just as with any estrogen therapy, to protect the uterine lining from overstimulation.
Finally, if a provider tells you that compounded biest is categorically safer than FDA-approved hormones, treat that claim with skepticism. The honest answer is that we do not have the head-to-head data to make that comparison. What we do know is that transdermal delivery appears safer than oral delivery for cardiovascular and clotting outcomes, and that applies equally to a compounded cream and an approved patch. The delivery route matters more than the label on the jar.