Authors: Dr Sav Zwickl and A/Prof Ada Cheung.
What are oestradiol implants?
An estradiol implant is a small, slow-release pellet containing the hormone oestradiol. Implants are inserted into the fatty tissue under the skin, preferably in the top of the buttock.
The Australian Informed Consent Standards of Care for Gender Affirming Hormone Therapy recommend a starting dose of 100mg every 6-12 months, and a maximum dose of 200mg every 6-12 months. In a recent survey, we asked trans people using oestradiol implants about the frequency of their implants, and the majority reported that their implant was replaced when their oestradiol blood concentrations fell below a certain level (57%), indicating the importance of regular blood tests. 15% of the people we asked, had their implant replaced 6 monthly, while 4% had it replaced every 9 months, and 8% yearly.
A trans woman speaking with a nurse. Credit: Renata Angerami via iStock.
Why do so few doctors prescribe implants?
Up until recently, only a handful of doctors Australia-wide were prescribing oestradiol implants and they were not listed in Australian prescribing guidelines until the release of the Australian Informed Consent Standards of Care for Gender Affirming Hormone Therapy in 2022.
We are now seeing an increasing number of doctors prescribe oestradiol implants, though implants are still not widely available. No implant is currently approved by the Australian Therapeutic Goods Administration. This means that estradiol pellets are an unlicensed product and are made by a compounding pharmacist. Compounded medications do not have regulations for quality control and lack testing for potency, efficacy, safety, and quality control.
Why do some trans people prefer implants over other oestradiol formulations?
Compared to other oestradiol formulations, such as tablets that are taken daily, implants are changed only every 6+ months. In our recently published study involving 53 trans people using oestradiol implants, almost all (93%) cited the long-lasting nature of the treatment as a key reason why they preferred implants over other formulations. Implants were often considered more convenient and led to a reduction in medication noncompliance.
Survey respondents using estradiol implants reported feeling implants were more effective (68%), resulted in better emotional wellbeing (49%), and had fewer side effects (42%) than other oestradiol formulations.
"I feel that the implants (2 x 100mg) are very effective.... I feel very healthy in general, better than ever, physically, and mentally."
-Alice, 22 years old.
"In the first 3 months of my first estrogen implant, I felt much more confident, resilient and like myself than I had before."
-Jessie, 38 years old.
"Generally, I have been very satisfied... The implants have been much better than Progynova tablets, which I found gave me itchy skin."
-Janet, 49 years old.
However, when we compared satisfaction with estradiol therapy and satisfaction with the physical effects of treatment, we found no difference in satisfaction between implant users and those trans people using other oestradiol formulations.
Does everyone prefer implants?
Like with any oestradiol formulation, implants work better for some people than others. For example, some trans people we surveyed described experiencing inconsistent oestradiol levels and side effects while using implants:
"I have found implants to be very inconsistent in their duration of action and the levels achieved. I... experience dangerous mental instability when [my] levels drop below a certain level."
-Leanne, 66 years old.
"Administration through implant is not ideal - a skyrocket rise and then steady decline over 6-12 months... I experienced menopausal symptoms... waiting for a new implant (hair loss, itchy skin, irritability, low mood)."
-Ella, 47 years old.
Oestradiol implants are considered as a non-reversible HRT, as the implant cannot be removed once inserted. It is important to make sure you can tolerate estradiol safely and without side effects before using an estradiol implant. For this reason, implants are used for continuing estradiol therapy, usually to replace other forms of estradiol and are not suitable for people commencing estradiol therapy. Implants are also not suitable for people planning to cease estradiol within the next twelve months, as although implants give a therapeutic effect for 6-12months, the residual implant may continue to release small amounts of estradiol for up to 18-24 months.
An individualised approach is best
The decision to use an implant will depend on the discussions you have with your doctor about your Individual circumstances. The risks and benefits of the oestradiol itself are the same as for any transdermal (via the skin) estradiol therapy, and you should ask your doctor specifically about any concerns you have regarding estradiol itself.
You can find more information about how to access to gender-affirming hormone therapy in Australia here. If you are interested in learning more about the effects and risks of oestrogen, progesterone, and anti-androgens you can check out our blog, the TransHub website, or refer to Australian and international treatment guidelines.
A trans woman and a non-binary person. Credit: Annie via Adobe Stock.
About the authors
Dr Sav Zwickl (they/them) is a non-binary researcher and educator who is passionate about improving the health and wellbeing of the trans community through research. They have a Masters degree in Sexology, a PhD in Gender, Sexuality and Diversity Studies, and experience working in peer support roles with LGBTIQA+ young people and sexual health education. Sav has been part of the Trans Health Research team since early 2019.
A/Prof Ada Cheung (she/her) is an Endocrinologist at Austin Health and a NHMRC & Dame Kate Campbell Research Fellow at The University of Melbourne. Driven by community need and working with the trans community, she established the Trans Health Research group and is an unwavering ally. She has won a number of national and international awards for research excellence and outstanding community leadership and is committed to training MD & PhD students and trans researchers.