If you’re on — or considering — feminizing gender-affirming hormone therapy, there’s a good chance your regimen includes two medications: estrogen, and something to block testosterone. That second medication, the antiandrogen (often just called a “blocker”), tends to get less attention than estrogen, but it does a lot of the work — and it’s responsible for many of the side effects patients ask about.
Here’s a clear guide to the blockers used in the U.S., what they do, what to expect, and how we monitor them — drawing on the WPATH Standards of Care (SOC-8) and the UCSF Gender-Affirming Care guidelines, the two references that anchor evidence-based GAHT.
Why Blockers Exist
Estrogen alone lowers testosterone, but for many people it doesn’t reliably bring testosterone into the typical female range on its own — especially at standard doses. Testosterone that remains active keeps driving the changes many patients want to pause: facial and body hair growth, scalp hair loss, erections, and oily skin.
An antiandrogen closes that gap, either by lowering testosterone production or by blocking its effects at the receptor. The combination — estrogen plus a blocker — is the standard feminizing regimen in the U.S., per both WPATH and UCSF.
That said, not everyone needs one. Some patients reach full suppression on estradiol alone (particularly with injectable estradiol), and anyone who has had an orchiectomy or vaginoplasty no longer needs a blocker at all. Whether you need one — and which — is an individualized decision made with your lab results in hand.
Spironolactone: The Workhorse
What it is: The most commonly used antiandrogen in American GAHT. It’s actually a potassium-sparing diuretic (a blood pressure medication) that happens to block androgen receptors and modestly lower testosterone production. Typical dosing ranges from 100–300 mg daily, usually split into two doses.
What to expect:
- You will pee more. It’s a diuretic — this is the most universal effect, most noticeable in the first weeks. Stay hydrated.
- Dizziness when standing up, especially early on or in hot weather, from its blood-pressure-lowering effect. Rise slowly; salt isn’t your enemy on spiro.
- Breast tenderness — often from the therapy overall, but spiro contributes.
- Increased thirst, occasional fatigue.
The one we watch closely: potassium. Spironolactone makes your body retain potassium, and levels that climb too high (hyperkalemia) can affect heart rhythm. This is why potassium monitoring is built into your lab schedule — per UCSF guidance, we check at baseline and periodically after starting or changing the dose. Practical advice: you don’t need to avoid bananas, but go easy on potassium supplements, salt substitutes (which are potassium chloride), and daily coconut-water habits.
Who should be cautious: people with kidney disease, those on certain blood pressure medications (ACE inhibitors, ARBs), and anyone with a history of high potassium. That’s a conversation, not necessarily a disqualifier.
Finasteride and Dutasteride: The Hair Medications
What they are: 5-alpha-reductase inhibitors. They don’t lower testosterone — they block its conversion to DHT, the more potent androgen responsible for scalp hair loss and much of facial and body hair coarseness.
Where they fit: These aren’t full blockers, and UCSF positions them as a secondary option — useful for people whose main concern is androgenic hair loss, as an add-on, or for people who can’t tolerate other blockers. Expect help with scalp hair retention; expect only a modest effect on facial hair, which usually still needs electrolysis or laser.
Side effects: generally well tolerated; some patients report mood changes or decreased libido. Worth flagging to us if you notice either.
GnRH Agonists: The Deep Suppressors
What they are: Injectable medications (like leuprolide) that shut down the signal from the brain that tells the body to make testosterone. They’re the most complete suppression available — WPATH SOC-8 describes them as highly effective — and they’re standard in some countries and in adolescent care.
Why they’re less common for U.S. adults: cost and insurance prior authorizations, mostly. When they’re accessible, they’re an excellent option — particularly for patients who can’t take spironolactone.
What to expect: injection-site soreness and, until estrogen is optimized, menopause-like symptoms — hot flashes being the classic one. Long-term suppression without adequate estrogen can affect bone density, which is one reason GAHT pairs suppression with estrogen rather than suppression alone.
A Word on Bicalutamide and Cyproterone
You may see bicalutamide discussed online — a receptor blocker from prostate-cancer care. Some clinics use it, but UCSF’s guidance remains cautious because of rare but serious liver toxicity and limited GAHT-specific safety data. If it ever makes sense in your care, that’s a deliberate, monitored decision — not a casual swap. Cyproterone acetate, common in Europe and Canada, isn’t available in the U.S.
What Changes to Expect When Your Blocker Is Working
With testosterone suppressed into the target range (typically under ~50 ng/dL, per UCSF):
- Erections become less frequent, then often minimal
- Body hair grows slower and finer (facial hair persists — hair removal handles that)
- Scalp hair loss slows or stabilizes
- Skin becomes less oily
- Libido commonly decreases (for some, a welcome quieting; for others, something to discuss and adjust around)
- With estrogen alongside: the feminizing changes on their own timeline — see our HRT timeline guide
What a blocker does not do: reverse established facial hair, restore lost scalp hair fully, or change voice or bone structure.
How We Monitor — and Why It’s Not Optional
Per WPATH and UCSF, blocker monitoring is straightforward but real:
- Total testosterone — confirming suppression into the target range
- Potassium and kidney function — for anyone on spironolactone, at baseline and periodically (more often after dose changes)
- Blood pressure — spiro lowers it; we want to know by how much
- Symptom check-ins — dizziness, mood, libido, and whether the regimen matches your goals
Labs are typically every 3 months in the first year, then every 6–12 months once stable — the same cadence as your estrogen monitoring, drawn in the same tube. More in our guide to blood work on HRT.
When Blockers End
Blockers aren’t necessarily forever. After orchiectomy or vaginoplasty, the body’s main testosterone source is gone and the blocker is discontinued — estrogen continues. Some patients also transition off spironolactone to estradiol monotherapy if injectable estradiol achieves suppression alone. Both are routine conversations as your care evolves.
Frequently Asked Questions
Do I have to take a blocker with estrogen?
Not always. If your testosterone suppresses fully on estradiol alone — which labs will show — monotherapy is reasonable per UCSF guidance. It’s individual, and it’s exactly what monitoring is for.
Why am I urinating so much on spironolactone?
Because it’s a diuretic before it’s a blocker. It’s expected, most prominent early, and worth building your hydration around.
Should I avoid high-potassium foods on spiro?
Normal foods are fine for most people with healthy kidneys. Avoid potassium supplements and salt substitutes, and keep your lab appointments — that’s what actually protects you.
My libido dropped. Is that permanent?
It’s a common and usually dose-related effect of suppression. If it bothers you, tell us — dose adjustments and regimen changes exist, and this is a quality-of-life conversation we take seriously.
Can blockers alone feminize without estrogen?
No — suppression without estrogen isn’t recommended. It forgoes the feminizing effects and risks bone health. The pair is the therapy.
What testosterone level are we aiming for?
Guidelines target the typical female physiologic range, generally under about 50 ng/dL, interpreted alongside how you actually feel and what your goals are.
This article is general health information, not medical advice, and it doesn’t create a patient relationship. Medication choices, doses, and monitoring are individual decisions made with a licensed clinician. If you’re an Eura Health patient, bring questions about your regimen to your next visit — or message us through the portal.