HRT Implants vs Injections for Perimenopause: What You Need to Know
HRT implants vs injections for perimenopause compared. Covers pellet delivery, duration, tachyphylaxis, UK and US availability, and who suits each.
Beyond Patches and Pills: Less Common HRT Delivery Routes
Most discussions of HRT focus on patches, gels, and tablets, but two other delivery methods exist: subcutaneous implants (sometimes called pellets) and injections. Both offer alternatives for women who find standard transdermal or oral routes inconvenient, insufficient, or poorly tolerated. They are less commonly prescribed in the UK compared to other countries, but interest in them is growing. Understanding how each works, what the clinical trade-offs are, and who is most likely to benefit helps women have more informed conversations with prescribing clinicians.
How HRT Implants Work
HRT implants are small pellets, typically about the size of a grain of rice, made of compressed crystalline estradiol or testosterone. A clinician inserts the pellet under the skin of the buttock or abdomen using a trocar under local anaesthetic. The pellet dissolves slowly over several months, releasing a steady stream of hormone directly into the surrounding tissue and then into the bloodstream. Because there is no daily action required after insertion, adherence is automatic for the duration of the implant. In the UK, estradiol implants are available through specialist menopause clinics, though they are not widely offered on the NHS. Testosterone implants are also available through private clinics.
The Problem of Tachyphylaxis With Implants
One clinical concern specific to implants is tachyphylaxis, a phenomenon where the body becomes accustomed to the hormone level provided by the implant and symptoms return before the implant is depleted. When this happens, serum estradiol levels may be high but the woman feels as though the implant has worn off. If a new implant is inserted at that point, the overall estradiol level rises further, and over successive cycles some women accumulate very high estradiol levels. Returning to other forms of HRT after discontinuing implants can take many months because circulating levels remain elevated while the residual implant material continues to release hormone. This is a reason many UK specialists are cautious about routine implant use.
HRT Injections: Options and Duration
Estrogen injections are used more widely in some countries than others. In the US, estradiol cypionate and estradiol valerate are available as oil-based intramuscular injections, typically given every one to four weeks depending on dose and individual response. In the UK, injectable estrogen is rarely prescribed for perimenopause, though testosterone injections are occasionally used for libido in women, usually as an off-label adaptation of male formulations. Injections produce hormone peaks and troughs rather than steady-state levels, and some women find the fluctuation noticeable in terms of symptom return toward the end of each injection cycle. Frequency of injection can be adjusted to smooth this out.
Availability in the UK vs the US
Implants are available in the UK through specialist private menopause clinics, with some NHS menopause services also offering them, though access is patchy. They are more commonly used in Australia and certain US states. In the US, testosterone and estradiol pellet therapy is offered by a wide network of private clinics, sometimes marketed aggressively with claims that go beyond what the evidence supports. Injections are more standardly available in the US through conventional endocrinology and gynaecology practices. UK women seeking implants should ensure their prescribing clinician follows British Menopause Society guidance and monitors serum estradiol levels to avoid accumulation.
Who Might Suit Implants or Injections
Implants may suit women who have significant difficulty adhering to daily or twice-weekly topical HRT, who have absorption issues with transdermal preparations, or who benefit from consistent hormone delivery without daily effort. They may also suit women who require testosterone replacement alongside estrogen and prefer a single procedure for both. Injections may suit women in healthcare systems where they are standard practice, or those who want a professional to administer their HRT rather than self-applying. Neither route is appropriate as a first-line choice. Both are typically considered after standard transdermal or oral routes have been tried.
Monitoring Is More Important With These Methods
Both implants and injections require closer laboratory monitoring than standard HRT routes. Serum estradiol levels should be checked regularly to ensure they remain within a safe and therapeutic range. With implants especially, monitoring before any re-insertion is important to avoid progressive hormone accumulation. Women pursuing these routes should be under the care of a clinician with specific experience in subcutaneous pellet therapy or injectable HRT rather than a general practitioner who prescribes these infrequently. Keeping a detailed symptom log helps track whether the current regime is working, and apps like PeriPlan let you log symptoms and track patterns over time to support those clinical conversations.
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