What is Estradiol Cypionate?
Estradiol Cypionate is the cypionate ester of the natural estrogen estradiol. The cypionate esterification extends the half-life to approximately 8-10 days, allowing weekly injections. It is used in research contexts to study hormonal balance, particularly in hormone replacement therapy and to understand estrogenic signaling.
Unlike anabolic steroids, estradiol cypionate does not work through androgen receptors but instead directly through classical estrogen receptors (ERα and ERβ).
This information is for research and educational purposes only. No medical advice.
Comparison
Estradiol and its counterparts
Compounds around estradiol, as described in the TPD lexicon. Tap a card to open its entry.
How it works
Estradiol Cypionate is hydrolyzed after injection to release estradiol, which acts via classical estrogen receptors and membrane-associated rapid signaling pathways. The cypionate moiety contributes to the depot effect, allowing longer dosing intervals.
- Binding to estrogen receptors α and β (ERα, ERβ) in various tissues
- Neuroendocrine effects: Negative feedback on LH/FSH at appropriate doses
- Cardiovascular: Estrogen influences lipid metabolism and endothelial function
- Skeletal muscle: Weak myotropic effects; not primarily anabolic like AAS
Where it acts
Where estradiol acts
Tap a point or a card. Grey = observed in human studies.
- Pituitary
Ovulation suppressed in all women (with progestin)7
Observed in trials - Testes
Testosterone below 50 ng/dl in 82.6%4
Observed in trials - Blood
Peak level after about 4 days, raised for about 11 days2
Observed in trials - Liver and vessels
No new liver marker rises and no blood clots in 40 young adults6
Observed in trials
Targets in the ChEMBL database10
Compound CHEMBL1200973: one recorded mechanism, agonist with direct binding to the human receptor.
Application and dosing
Dosing
Dosing, titration and syringe
Loading the dosing information …
- Getting started and stepping up, drawn as a staircase
- Units on the U-100 syringe for every step
- How long one vial lasts
What the research shows
Studies on estradiol cypionate are limited compared to synthetic estrogens. Available data shows:
- Effective hormone replacement profiles in studies with good tolerability at appropriate dosing
- Safety: Estrogen-related concerns such as blood clotting and breast cancer are dose-dependent and occur primarily at high physiological or supraphysiological doses
- Lipid profiles: Estradiol can raise HDL cholesterol and slightly lower LDL
- Bone health: Positive effects on bone density at adequate doses
Study results
What the trials measured
Interactive: switch tabs, tap points, show or hide arms. Arms are named relative to each other, no dosing advice.
Three estradiol esters after one injection2
Days, about 10 participants each, own hormone production suppressed by the pill
Abstract values are approximate: peak after about 4 or 2 days, raised for about 11, 7 to 8 and 4 to 5 days (chart shows the middle of the range). Cypionate reached lower peaks, the authors found valerate the most predictable.
Injections in trans women346
Share in percent, three analyses of treatment data
In the largest analysis most were above 200 pg/ml, ester and route (muscle or under the skin) made no difference. A review therefore considers the guideline starting doses too high. In the small group with cypionate under the skin many could not adjust because of supply shortages.
Research status
Where the research stands
Estradiol Cypionate has been approved for decades. The registry lists only a few trials, mostly on the monthly injection with a progestin. As of 25 Oct 2026. 11
- Preclinical Action on the estrogen receptor
- Phase 1 1 trial, 1 completed
- Phase 2 2 trials, 1 completed, 1 stopped early
- Phase 3 no registered trial
- Approval in the USA, prescription only
Show all 2 phase 2 trials on a timelineHide timeline
NCT01699022 · 17 participants, started Jun 2010, primary endpoint reached Jul 2011. Tests several agents.
Registry entry ↗ · Results: Thurman et al., Contraception, 2013
NCT04865029 · 10 participants, started Jul 2021, stopped early Jan 2022. Tests several agents.
Bar: start to primary endpoint (planned for running trials). Green = completed, blue = progress until 25 Oct 2026, grey = stopped early. Phase 1: 1 trial on safety and pharmacokinetics, not shown as bars.
Side effects
Estradiol Cypionate side effects are typically estrogen-related and dose-dependent:
- Endocrine: Breast tenderness or enlargement, emotional lability, possible libido changes
- Cardiovascular: High blood pressure (at high doses or in sensitive individuals), fluid retention
- Metabolic: Potential triglyceride elevation (typical for estrogen), glucose intolerance risk
- Thrombosis: Increased risk in older individuals or with risk factors (smoking, obesity)
- Hepatic: Ester form minimally hepatotoxic; liver enzyme changes rare
- Other: Headaches, nausea, gastrointestinal upset (especially initially)
Storage
Estradiol Cypionate oil must be stored at room temperature, protected from light.
- Temperature: 15-25°C ideal
- Light: Store in dark (original vials or amber glass)
- Moisture: Keep dry
- Shelf life: 2-3 years stable with proper storage
- Caution: Crystallization may occur at cold temperatures - do not store in freezer
