Testosterone Undecanoate vs Cypionate Dosing

Testosterone undecanoate and testosterone cypionate treat the same condition but on completely different timetables: undecanoate (Aveed) is a deep-muscle depot dosed at 750 mg every 10 weeks in a clinic, while cypionate is a small home injection of roughly 100–200 mg every week. They are not interchangeable milligram-for-milligram — undecanoate's enormous 3 mL oil depot releases over more than a month, so its average weekly testosterone delivery is far lower than its big injection number suggests.

TL;DR — key takeaways

• Different timetables. Undecanoate is dosed every 10 weeks (after a 4-week loading injection); cypionate is dosed weekly or twice weekly. You cannot map one schedule onto the other.
• Different injection. Undecanoate is a 3 mL deep gluteal injection given in a healthcare setting with a 30-minute observation period; cypionate is a small 0.3–1 mL injection most people give themselves.
• Heavier ester. The undecanoate chain is so large that only about 63% of each milligram is testosterone, versus about 69% for cypionate.
• Units still follow concentration. For cypionate, whether you draw 35 or 70 units depends on the mg/mL strength of your vial — not the ester name.

Why one extra-long ester changes everything

Both drugs are testosterone with a fatty-acid ester bolted to the 17-beta hydroxyl group, and the body cannot use the ester — only the testosterone released when enzymes cleave it off. Cypionate carries an eight-carbon cyclopentylpropionate chain. Undecanoate carries an eleven-carbon chain, the longest in common clinical use. That extra length makes the molecule dramatically more fat-loving, so the oil depot it forms after injection releases its payload over weeks rather than days.

The result is a half-life measured in weeks, not days: intramuscular testosterone undecanoate in castor oil has a terminal half-life around 21–34 days, compared with roughly 5–8 days for cypionate. That single property is why undecanoate can be injected as infrequently as every 10 weeks while cypionate needs a top-up every week or two to avoid a trough. The long tail is also why undecanoate uses a loading schedule — a second injection at week 4 — to reach steady state faster.

The trade-off for that convenience is volume and setting. A maintenance undecanoate dose is 750 mg in 3 mL of oil, far too large for a small insulin syringe, and it is injected slowly and deeply into the gluteal muscle. Because rare pulmonary oil microembolism (POME) and anaphylaxis reactions have been reported during or just after the injection, the FDA label requires it to be given in a healthcare setting with a 30-minute observation window through a restricted (REMS) program.

Side-by-side: the two formulations at a glance

*After an initial 750 mg dose, a second is given 4 weeks later, then every 10 weeks. Figures reflect the FDA-approved Aveed and Depo-Testosterone prescribing information; the EU formulation (Nebido) uses 1000 mg every 10–14 weeks. Always follow your prescriber's protocol.

Release curves, visualised

The shapes tell the whole story. Cypionate produces a weekly sawtooth — a peak after each injection, a dip before the next — while undecanoate forms one long, slow hump that spans the entire 10-week interval.

The curves are illustrative of the relative shapes, not exact serum values. The practical point is that undecanoate trades the weekly peaks and troughs of cypionate for one broad, slow curve — fewer injections, but a much larger single dose and far less day-to-day control.

Turning each dose into volume and units

For cypionate the familiar maths applies: a U-100 insulin syringe holds 100 units per 1 mL, so divide the dose by the concentration to get mL, then multiply by 100 to get units. Undecanoate is different in kind — its 3 mL volume will not fit an insulin syringe at all, so it is measured in mL with a standard 3 mL syringe and a long intramuscular needle.

Cypionate dose-to-units reference chart

Common weekly cypionate doses shown as units on a U-100 syringe at the two most common concentrations. Undecanoate is omitted because it is dosed by mL every 10 weeks, not by weekly units. Always confirm against your own vial label.

Note the gap at 160 mg / 100 mg/mL: that draw is 1.6 mL, more than a 1 mL syringe holds, so higher doses on a weak vial need a split injection or a stronger vial.

How this is calculated

The cypionate figures use two facts only: a U-100 syringe holds 100 units per mL, and concentration is dose-divided-by-volume. The undecanoate figures use the same volume arithmetic (mg ÷ mg/mL = mL) but stop there, because the dose is too large for unit-based insulin syringes. The weekly-average and ester-weight numbers are simple ratios — total dose ÷ interval, then × the testosterone fraction (about 0.63 for undecanoate, 0.69 for cypionate). The TRT dose calculator automates the cypionate conversions so you can sanity-check them against the chart. None of this is medical advice; it is the maths behind a dose your prescriber has set.

Frequently asked questions