What Is Estradiol Cypionate? Dosage, Half-Life & How to Track It
Also known as: Depo-Estradiol · Estradiol cypionate injection · E2 Cyp · Estradiol cipionate
Estradiol cypionate is estradiol attached to the cypionate ester, an oil-soluble chain that slows its release for a roughly weekly or biweekly injection instead of daily dosing. Its ester half-life runs around 5 days, though individual absorption from the oil depot varies more than with testosterone esters. It is the injectable option in gender-affirming feminizing HRT and, less commonly today, in menopausal hormone therapy. Educational only; estrogen dosing and monitoring are set by your prescriber.
What estradiol cypionate is and how it works
Estradiol cypionate is estradiol — the primary estrogen your body makes — bonded to a cypionate ester, the same oil-soluble carbon chain used in testosterone cypionate. The ester’s job is identical: it makes the molecule sit in a depot at the injection site and release gradually as enzymes cleave it away, leaving free estradiol to act at estrogen receptors throughout the body.
The dominant modern use is feminizing gender-affirming hormone therapy, where injectable estradiol is valued for producing more stable levels than oral estrogen and for skipping the liver’s first-pass metabolism (oral estrogen doesn’t avoid this, which raises clotting-factor concerns some prescribers weigh against injectable or transdermal routes). It also has a long history in cisgender women’s HRT for menopausal symptoms, though oral tablets and transdermal patches have largely replaced injections in that setting.
Weight-wise, the ester is a smaller share of the molecule than you might expect: roughly 69% of the milligrams in estradiol cypionate are estradiol itself, similar to testosterone cypionate’s ~70% split.
Dosing math & the mg/mL trap
Like testosterone esters, estradiol cypionate is labeled by concentration — milligrams per milliliter — not total mg per vial. Depo-Estradiol and compounded equivalents are commonly supplied around 5 mg/mL, and the same rule applies: a 10 mL vial at 5 mg/mL holds 50 mg, not 5 mg.
The conversion is the same one-line formula as any ester: volume (mL) = dose (mg) ÷ concentration (mg/mL). Gender-affirming protocols commonly run in the 2–10 mg per week (or biweekly) range, titrated against estradiol labs rather than a fixed target dose.
| Dose | 5 mg/mL | 10 mg/mL |
|---|---|---|
| 2 mg | 0.40 mL (40u) | 0.20 mL (20u) |
| 4 mg | 0.80 mL (80u) | 0.40 mL (40u) |
| 5 mg | 1.00 mL (100u) | 0.50 mL (50u) |
| 10 mg | 2.00 mL (200u) | 1.00 mL (100u) |
Volume to draw for common doses at two concentrations (U-100 syringe units in parentheses). Compounded pharmacies vary in concentration more than commercial testosterone does, so it’s worth confirming the vial’s mg/mL before drawing a dose.
Half-life & what it means for frequency
The cypionate ester’s terminal half-life is commonly cited around 5 days, shorter than testosterone cypionate’s ~7–8 days. In practice, estradiol esters are also known for more individual variability in how fast they absorb from the oil depot than testosterone esters, which is part of why estradiol levels are checked and doses adjusted more often early in a protocol.
That variability, plus the shorter half-life, is why weekly dosing is more common than the biweekly-to-monthly schedules sometimes used historically — a shorter, more frequent injection produces a flatter, more predictable curve than trying to stretch the interval.
What to track & side effects
The lab that matters most is serum estradiol, typically targeted in the 100–200 pg/mL range (mid-normal premenopausal levels) for feminizing HRT, checked at a consistent point in the injection cycle so results are comparable week to week. Testosterone (to confirm suppression, if that’s a treatment goal) and prolactin are commonly tracked alongside it.
Estrogen therapy carries a well-documented blood-clot (VTE) risk, generally considered lower with injectable or transdermal routes than oral estrogen since both skip first-pass liver metabolism — smoking history and clotting history are standard things a prescriber screens for. Injection-site soreness is the most common minor side effect.
How to track Estradiol Cypionate in Stackeddd
Log each injection with its dose and site, and keep serum estradiol trending next to the protocol so a lab result carries its injection-cycle context instead of floating free. Since estradiol cypionate is sold at more variable concentrations than testosterone, running the vial through the calculator once locks in the right volume.
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Blood-Level Simulator
Model it yourself: pick Estradiol Cypionate, set your dose and injection frequency, and see the steady-state curve between shots — the same pharmacokinetic engine that runs inside the app.
Related compounds
Related reading: TRT Math: what mg/mL actually means · Injection frequency: daily vs EOD vs weekly
Frequently asked questions
What is estradiol cypionate used for?
It’s the injectable estrogen most often used in feminizing gender-affirming hormone therapy, valued for producing more stable levels than oral estrogen while skipping the liver’s first-pass metabolism. It also has a history in menopausal HRT, though oral and patch forms are more common there today.
What is the half-life of estradiol cypionate?
Roughly 5 days, based on the cypionate ester’s depot release — somewhat shorter than testosterone cypionate’s ~7–8 days. Individual absorption from the oil depot is also more variable with estradiol esters than with testosterone.
What estradiol level is targeted on injectable HRT?
Feminizing protocols commonly target the 100–200 pg/mL range, roughly mid-normal premenopausal levels, checked at a consistent point in the injection cycle so results are comparable week to week.
Is injectable estradiol safer than oral estrogen?
Injectable (and transdermal) estrogen skips the liver’s first-pass metabolism, which is associated with a lower blood-clot (VTE) risk than oral estrogen in the literature. It isn’t risk-free — smoking and clotting history are still standard screening questions for any route.
This is educational information, not medical advice. Doses and protocols above reflect published references and community practice — protocol decisions belong with your prescribing physician. Generic names used throughout. How this reference is built & how the AI is tested →
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