Decoding the Dose: What is in Hormone Pellets?

October 7, 2025 •

4 min read

In 2023/24, over 13 million Hormone Replacement Therapy (HRT) items were prescribed by the NHS in England, a 22% increase from the previous year [1.9.1]. A growing option within HRT is pellet therapy, but what is in hormone pellets? These tiny implants contain bioidentical hormones designed to restore balance [1.2.1].

Quick Summary

Hormone pellets primarily contain bioidentical hormones, such as estradiol and/or testosterone, derived from plant sources like yams and soy [1.10.2, 1.10.3]. They also include minimal inactive ingredients, like stearic acid or cholesterol, which act as binders [1.6.1, 1.6.3].

Key Points

Active Ingredients: Pellets contain bioidentical hormones, primarily estradiol and/or testosterone, which are molecularly identical to human hormones [1.3.1].
Plant-Derived: These hormones are synthesized in a lab from compounds found in plants like wild yams and soy [1.10.2, 1.10.3].
Inactive Binders: A very small amount of a binder, such as stearic acid or cholesterol, is used to hold the powdered hormone in a solid pellet form [1.6.1, 1.6.3].
Compounded vs. FDA-Approved: Most pellets are custom-compounded and not directly approved by the FDA, unlike standardized, FDA-approved products like Testopel® [1.7.2, 1.7.5].
Consistent Release: The main advantage is the steady, long-term release of hormones, avoiding the fluctuations seen with other methods like pills or creams [1.2.4].
Implantation: Pellets are inserted under the skin in a minor office procedure, where they slowly dissolve over 3 to 6 months [1.2.4].
Customization: Compounded pellets allow for personalized dosages based on a patient's specific hormonal needs determined by blood tests [1.8.1].

The Core Components of Hormone Pellets

Hormone pellets are a form of bioidentical hormone replacement therapy (BHRT) designed to alleviate symptoms of hormonal imbalance in both men and women [1.2.1]. These small, rice-sized cylinders are inserted subcutaneously (under the skin), typically in the hip or lower abdominal wall, where they release a steady, consistent dose of hormones over several months [1.2.1, 1.2.4]. This delivery method avoids the fluctuations often seen with pills, creams, or patches [1.2.2].

The primary ingredients can be broken down into two categories: active hormones and inactive binders.

Active Ingredients: Bioidentical Hormones

The term "bioidentical" signifies that the hormones are molecularly identical to those produced naturally by the human body [1.3.1]. This structural match allows them to be recognized and utilized by the body's hormone receptors effectively [1.10.4]. The active hormones in pellets are synthesized from plant sources, most commonly wild yams or soy [1.10.2, 1.10.3]. A laboratory process converts a steroid ring from these plants into the desired hormones.

The most common bioidentical hormones found in pellets are:

Estradiol: This is the primary form of estrogen active in the body. Estradiol pellets are used to treat symptoms of perimenopause and menopause in women, such as hot flashes, night sweats, vaginal dryness, and bone density loss [1.8.1].
Testosterone: Used in both men and women, testosterone pellets can help improve low libido, increase energy levels, enhance mental clarity, and promote muscle mass and bone density [1.8.1].
Progesterone: While less common in pellet form, some formulations may include progesterone [1.2.1, 1.4.5].
Anastrozole: Some testosterone pellets for men may be compounded with anastrozole, an aromatase inhibitor, to prevent the conversion of testosterone into estrogen [1.6.3].

Inactive Ingredients: Binders and Fillers

To create a solid, implantable pellet, the powdered hormone must be compressed using a binder. These inactive ingredients typically make up a very small fraction of the pellet's total composition [1.6.3].

Stearic Acid: This is a common, naturally occurring fatty acid used as a binder or lubricant in the manufacturing process [1.5.1, 1.6.5]. In many cases, it makes up less than 0.1% of the pellet and is considered clinically negligible [1.6.3]. The FDA-approved testosterone pellet, Testopel®, contains 75mg of testosterone, 0.97mg of stearic acid, and 2mg of polyvinylpyrrolidone [1.6.4].
Cholesterol: Some compounding pharmacies use cholesterol as a binder [1.6.1]. Proponents suggest that because cholesterol is a naturally occurring substance in the body, it may lead to fewer side effects like inflammation or pellet extrusion (the pellet working its way out of the skin) [1.6.3].

Compounded vs. FDA-Approved Pellets

It is crucial to understand the distinction between custom-compounded pellets and FDA-approved versions. The vast majority of bioidentical hormone pellets are prepared by compounding pharmacies [1.2.4]. These pharmacies create customized dosages based on a physician's prescription for an individual patient [1.5.4]. While the active hormones themselves (estradiol, testosterone) are FDA-approved substances, the specific compounded pellets are not individually tested or approved by the FDA for safety, purity, and efficacy [1.8.1, 1.7.4].

The American College of Obstetricians and Gynecologists (ACOG) recommends that FDA-approved hormone therapies be used over compounded versions due to the lack of robust data on the safety and efficacy of the latter [1.7.2]. However, organizations also note that compounded therapies may be necessary for patients who have allergies to ingredients in FDA-approved products or require a dosage not commercially available [1.7.5]. Quality compounding facilities, particularly FDA-registered 503B outsourcing facilities, adhere to stringent standards for purity and consistency [1.4.5].


Feature	Compounded Bioidentical Pellets	FDA-Approved Pellets (e.g., Testopel®)
Approval	The final product is NOT FDA-approved. Made in compounding pharmacies [1.7.2].	The final product (e.g., Testopel®) is FDA-approved for specific indications [1.6.4, 1.7.5].
Customization	Dosages are highly customizable to the individual patient's needs based on lab work [1.8.1].	Available only in standardized, fixed doses (e.g., 75mg testosterone) [1.6.4].
Hormone Types	Commonly include estradiol, testosterone, and sometimes progesterone or other substances [1.4.5].	Primarily limited to testosterone (Testopel®). No FDA-approved estradiol pellet exists [1.7.2].
Inactive Ingredients	Typically contain stearic acid or cholesterol as a binder [1.6.1, 1.6.3].	Specific, listed inactive ingredients, such as stearic acid and polyvinylpyrrolidone [1.6.4].
Oversight	Regulated by state pharmacy boards. Quality can vary. 503B facilities have higher standards [1.4.5].	Subject to rigorous FDA oversight for manufacturing, safety, and effectiveness [1.7.5].

Potential Benefits and Risks

The primary benefit of pellet therapy is the consistent, long-lasting delivery of hormones, which can lead to significant relief from symptoms like fatigue, mood swings, and low libido [1.8.1]. This steady state avoids the hormonal peaks and valleys associated with other delivery methods [1.2.4]. However, risks exist. Side effects can include acne, hair growth, mood changes, and weight gain [1.8.1]. A significant drawback is the inability to easily adjust the dose once a pellet is inserted; if side effects occur, the patient must wait several months for the pellet to dissolve [1.8.2]. Complications at the insertion site, though rare, can include bruising, infection, or extrusion of the pellet [1.2.4, 1.8.3].

Conclusion

Hormone pellets are primarily composed of bioidentical estradiol or testosterone derived from plants, fused into a solid form with a minimal amount of an inactive binder like stearic acid or cholesterol [1.5.1, 1.10.2]. While offering the convenience of a long-lasting, steady hormone dose, most pellets are custom-compounded and lack FDA approval for the final product [1.7.2]. Patients considering this therapy should have a thorough discussion with a healthcare provider about the differences between compounded and FDA-approved options, as well as the potential benefits and risks associated with this unique delivery system.

For more information from a regulatory perspective, one can review guidance from professional organizations. The American College of Obstetricians and Gynecologists (ACOG) provides clinical consensus on the topic. https://www.acog.org/clinical/clinical-guidance/clinical-consensus/articles/2023/11/compounded-bioidentical-menopausal-hormone-therapy

Frequently Asked Questions

Bioidentical hormones are hormones that have the exact same chemical and molecular structure as the hormones naturally produced by your body. They are typically derived from plant sources like yams or soy and processed in a lab [1.2.2, 1.3.1].

Yes, the active hormonal ingredients in bioidentical pellets, like estradiol and testosterone, are synthesized from compounds found in plants such as wild yams and soy [1.10.2, 1.10.3].

Stearic acid is a common, safe, inactive ingredient used as a binder to press the powdered hormone into a solid pellet. In many formulations, it acts only as a lubricant during production and is present in clinically negligible amounts [1.6.3, 1.5.1].

No. While the hormones themselves (like testosterone) are FDA-approved substances, most bioidentical pellets are custom-made in compounding pharmacies and are not individually approved by the FDA for safety and efficacy. There is an FDA-approved testosterone pellet called Testopel® [1.7.2, 1.6.4].

Hormone pellets typically last between 3 to 5 months for women and 4 to 6 months for men. The pellet dissolves completely on its own over this time and does not need to be removed [1.2.2, 1.2.4].

Besides the active bioidentical hormone (e.g., testosterone or estradiol), a pellet contains a very small amount of an inactive binder. This is usually stearic acid or cholesterol, which holds the pellet together [1.6.1, 1.6.3].

Allergies are very rare. The hormones are identical to your body's own. The binders, like stearic acid, are common in many products (including aspirin) and rarely cause reactions. A soy allergy is not a concern as the final hormone molecule is different from the soy protein that causes allergies [1.3.2, 1.2.5].