Do I actually need a blocker?

Not always, and not forever. Most feminising patients use one early on to get testosterone down while oestrogen builds up. Once oestrogen is well established, or after orchidectomy or genital surgery, many people reduce or stop the blocker entirely. We review it with you at each appointment.

Which blocker will I be offered?

It depends on your bloods, your other health, and your preferences. In the UK the two most common are cyproterone acetate (a low-dose daily tablet) and GnRH analogues (a 12-weekly injection or implant for the most complete suppression). Bicalutamide is chosen when preserving sexual function matters; spironolactone when the others don't suit.

Why don't you use spironolactone as standard like US clinics?

Spironolactone blocks the androgen receptor but doesn't lower testosterone production much, and it brings diuretic effects (more urination, potassium monitoring). UK and European practice tends to prefer cyproterone or GnRH analogues for more complete suppression, but spironolactone is a good option in the right situation.

Can I stop my blocker after surgery?

Usually yes. After orchidectomy, or vaginoplasty with removal of the testes, your body no longer produces significant testosterone, so the blocker is generally stopped. We confirm with bloods and adjust your oestrogen accordingly.

What's the testosterone flare with GnRH analogues?

In the first week or two a GnRH analogue briefly stimulates testosterone before it shuts production down. We plan for this, sometimes by continuing another blocker over the changeover, so it's rarely a problem in practice.

Are blockers reversible?

Yes. Their effect on testosterone reverses once you stop. Any feminising changes that came from oestrogen are a separate matter: the blocker itself simply lowers testosterone while you take it.

Home / Medication guides / Testosterone Blockers

TRANS-FEMININE HRT · MEDICATION GUIDE

Testosterone Blockers therapy, a clear guide.

Testosterone blockers (anti-androgens) reduce the amount of testosterone your body makes, or stop it acting, so oestrogen can do its work. Most feminising patients start on one, and many can step down or stop once oestrogen alone holds testosterone low. This guide covers every blocker we prescribe and how we choose between them.

Begin your journey See payment plans

Drug class

Anti-androgens / GnRH analogues

Used for

Feminising HRT: T suppression

Routes

Oral, IM, SC implant

Frequency

Daily → 12-weekly

Prescription

Specialist initiation

Often temporary

May stop once stable or post-op

On this pageOverview How it works The options Side effects Cost FAQ

OVERVIEW

What testosterone blockers does, in plain English.

Testosterone is the hormone behind most of the traits that feminising HRT aims to soften. Oestrogen lowers it to a degree on its own, but many patients need a blocker as well, at least early on, to get testosterone down into the range where feminisation proceeds smoothly (the clinic aims for testosterone below 3 nmol/L, with oestradiol in the 400-800 pmol/L target range).

Blockers fall into two camps: those that switch off production at the source (GnRH analogues, and cyproterone in part) and those that sit on the androgen receptor so testosterone can't act (spironolactone, bicalutamide). Which one suits you depends on your bloods, other health conditions, whether you'd rather take tablets or have an injection, and your own preferences.

Not everyone needs one forever.

A blocker is a means to an end, not a life sentence. Once oestrogen is well established, or after orchidectomy or genital surgery, most patients reduce or stop the blocker. We review it with you at every appointment.

HOW IT WORKS

The way it actually works.

The goal is simple: get testosterone low enough that oestrogen can drive feminisation, and keep it there safely. We do that either by telling the pituitary to stop signalling the testes (GnRH analogues), by dampening production and blocking the receptor at once (cyproterone), or by blocking the receptor alone while testosterone levels stay put (spironolactone, bicalutamide).

Suppress production

GnRH analogues and cyproterone lower how much testosterone the body actually makes.

Block the receptor

Spironolactone and bicalutamide stop testosterone acting, even if the blood level doesn't fall much.

Let oestrogen do more

With testosterone suppressed, a lower, safer oestrogen dose achieves better feminisation.

Often a bridge

Many patients taper off the blocker once oestrogen alone suppresses, or after surgery.

FORMS & DOSING

Multiple ways to take it. Your choice, our guidance.

There's no single right answer. What matters is what fits your life. Most patients start on the simplest option and switch later if it suits.

IM / SC / SC implant · Every 4-12 weeks

GnRH analogues

Prostap · Decapeptyl · Zoladex

The most effective blockers we use. They switch off the pituitary signal that drives testosterone production, giving very low, very stable levels. Usually given by a clinician; Prostap can be self-administered at home after a one-off training session and signed consent. Prostap (leuprorelin) is a subcutaneous depot and our most commonly prescribed option; Decapeptyl (triptorelin) is an intramuscular alternative; Zoladex (goserelin) is a small implant placed under the skin of the abdomen.

Typical dose: Prostap 11.25 mg every 12 weeks (a 4-weekly form also exists); Decapeptyl 11.25 mg every 12 weeks (or 3 mg every 4 weeks); Zoladex 10.8 mg every 12 weeks.

Pros

Most complete testosterone suppression

Very stable, nothing daily to remember

Favourable safety profile; fully reversible

Allows lower oestrogen doses

Watch-outs

Usually clinician-administered (Prostap self-injection possible after training)

Higher cost than tablets privately

A brief testosterone "flare" in the first weeks

Injection or implant-site reactions in some

Oral tablet · Daily

Cyproterone acetate

Androcur · Generic CPA

The most commonly prescribed oral blocker in UK and European gender care. A progestogen that both lowers testosterone production and blocks the receptor, so it works well at low doses. We deliberately keep the dose low because the risks that matter (liver enzymes, raised prolactin and, rarely, meningioma) are linked to higher, longer exposure.

Typical dose: 6.25-12.5 mg daily (low-dose). Not available in the USA.

Pros

Very effective at low, inexpensive doses

Tablet, no injections

Progestogenic effect may aid breast development

Watch-outs

Needs LFT and prolactin monitoring

Small meningioma risk at high cumulative doses (why we dose low)

Can cause fatigue or low mood in some

Oral tablet · Once–twice daily

Spironolactone

Aldactone · Generic

A potassium-sparing diuretic with anti-androgen activity: it blocks the androgen receptor rather than lowering testosterone production much. It is the standard blocker in the USA but used more selectively in the UK, often where cyproterone or a GnRH analogue is unsuitable.

Typical dose: 50-200 mg daily, titrated.

Pros

Useful when other blockers are unsuitable

Tablet, no injections

Long track record

Watch-outs

Can raise blood potassium, needs U&E monitoring

Diuretic: more urination, thirst, lower blood pressure

Blocks the receptor without dropping testosterone much

Oral tablet · Daily

Bicalutamide

Casodex · Generic

A pure androgen-receptor blocker used off-label in gender care. Because it works at the receptor, blood testosterone stays normal or even rises slightly, which some patients prefer as it tends to preserve libido and erectile function. Used selectively, with liver monitoring.

Typical dose: 25-50 mg daily.

Pros

Blocks androgens while preserving sexual function

Tablet, no injections

No diuretic effects

Watch-outs

Off-label for gender care

Rare but serious liver toxicity, needs LFT monitoring

Less long-term trans-specific data

SIDE EFFECTS & RISKS

What to watch for, and what to tell us.

Most side effects come from testosterone falling: that's the point, and many are the same things any body feels with low testosterone. A few are specific to individual blockers, which is why the monitoring differs by drug. Always tell us if something doesn't feel right; switching blocker often fixes it.

Common

Lower libido and erections +

Expected as testosterone drops. Bicalutamide is the blocker least likely to affect this. Raise it if it bothers you.

Fatigue or low energy +

Common in the first weeks, especially with cyproterone. Usually settles; if not, we adjust dose or switch.

Mood changes +

Some patients feel flatter or more tearful as levels shift. Tell us: dose or choice of blocker can help.

More urination (spironolactone) +

Its diuretic effect means peeing more and feeling thirsty, particularly early on.

Hot flushes +

With strong suppression (GnRH analogues) before oestrogen is fully established.

Less common / serious

Raised prolactin (cyproterone) +

CPA can raise the hormone prolactin. We check it; if it climbs we lower the dose or switch. Usually reversible.

Liver enzymes (cyproterone, bicalutamide) +

Both can raise liver enzymes. We check LFTs at baseline and during monitoring, and act early if they rise.

Meningioma (cyproterone) +

A small increase in the risk of this usually-benign brain-lining tumour is linked to high, prolonged CPA doses, which is exactly why we keep the dose low and time-limited.

High potassium (spironolactone) +

Spironolactone can raise blood potassium, occasionally dangerously. We monitor U&E, and it needs care in kidney problems.

Testosterone flare (GnRH analogues) +

A brief rise in testosterone in the first 1-2 weeks before suppression sets in. We plan for it, sometimes overlapping another blocker briefly.

Bone density +

Very low sex-hormone levels over years can thin bone, but adequate oestrogen protects against this, which is why blocker and oestrogen go together.

Monitoring schedule

We catch things early. Here's the routine you can expect.

Most of the testing is front-loaded while we fine-tune your dose. Once your levels are stable, it's usually just once a year.

Baseline

Testosterone & oestradiol

U&E (potassium/renal)

LFTs

Prolactin (if CPA)

3–6 months

Testosterone (suppression)

U&E if on spironolactone

LFTs / prolactin if on CPA

6-monthly while adjusting

Testosterone & oestradiol

U&E, LFTs

Prolactin (CPA)

Yearly once stable

Full hormone panel

U&E, LFTs

Symptom & dose review

COST

What testosterone blockers costs you, monthly.

Your monthly plan covers the clinical side: appointments, prescriptions, letters. Medication is paid at the pharmacy, and the price depends heavily on which blocker: the oral options are inexpensive, GnRH analogues cost more privately. Once your GP takes over under shared care, most items drop to the standard NHS prescription charge. The figures below are approximate and worth confirming with your pharmacy.

Cyproterone acetate (private)

~£5-10 per month

Low-dose generic

Spironolactone (private)

~£5-10 per month

Generic tablet

Bicalutamide (private)

~£10-20 per month

Generic tablet

GnRH analogue (private)

~£70-100 per 12 weeks

Prostap / Decapeptyl / Zoladex

Once on shared care

£9.90 per item

Standard NHS Rx charge

See full payment plan

FREQUENTLY ASKED

Questions, answered.

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