What Does mg Per Week Mean for Testosterone?

What "mg per week" actually describes

Injectable testosterone esters — cypionate and enanthate are the common ones — sit in an oil depot and release slowly over days, so clinicians prescribe by the weekly total rather than per dose. The Endocrine Society's hypogonadism guideline frames therapy around reaching mid-normal serum testosterone and monitoring it, which is a function of total drug delivered per week, not the size of any single shot (Bhasin et al., 2018). The weekly figure is the lever; injection frequency mostly changes how smooth the peaks and troughs are.

The number on your prescription is a mass in milligrams. A syringe measures volume in mL or in U-100 units. They are linked by concentration — how many mg sit in each mL of oil. A standard FDA-labelled testosterone cypionate vial is 200 mg/mL (DailyMed, Hikma label), but compounded and international products are often 100 or 250 mg/mL, and that single number is what changes your draw.

Keep dose and volume mentally separate. The dose is what your body sees; the volume is what your eyes line up against the barrel. Getting the two confused — reading "50" as 50 mg when it is actually 50 units of a 200 mg/mL oil (which is 100 mg) — is the classic beginner error.

How this is calculated

Two steps turn a weekly mg figure into something you can draw:

1. Per-injection mg = weekly mg ÷ injections per week.
2. Volume in mL = per-injection mg ÷ concentration (mg/mL).
3. U-100 units = mL × 100 (because 1 mL = 100 units on a U-100 insulin syringe — see U-100 syringe units explained).

Worked through once: 140 mg/week, injected twice weekly, on a 200 mg/mL vial. Per injection = 140 ÷ 2 = 70 mg. Volume = 70 ÷ 200 = 0.35 mL. Units = 0.35 × 100 = 35 units. The weekly total never changed; we just sliced it and converted each slice. Pharmacokinetic data comparing IM and subcutaneous testosterone confirm the total weekly exposure is what matters, while route and frequency mainly affect tolerability and steadiness (Spratt et al., 2018; Schürmeyer et al., 1984).

Weekly mg to mL and units, by concentration

This chart assumes a single weekly injection so you can read the full weekly dose as one draw. If you split the dose, divide the mL and units by the number of injections (the worked examples below do exactly that).

Notice the same 100 mg/week is 100 units on a 100 mg/mL oil but only 50 units on 200 mg/mL. The dose is identical; the concentration halved the volume. This is why copying someone else's "units" without checking their vial strength is unsafe.

Worked examples: splitting a weekly dose

Common mistakes with weekly dosing

The first error is treating the syringe number as milligrams. "Draw to 40" on a U-100 syringe is 40 units = 0.40 mL, which on a 200 mg/mL vial is 80 mg — not 40 mg. The second is copying a friend's units without matching concentration: 50 units of 100 mg/mL is 50 mg, but 50 units of 250 mg/mL is 125 mg. Same mark, very different dose.

A third is forgetting that splitting does not lower the weekly dose — some beginners halve a twice-weekly dose and the weekly total, accidentally taking a quarter of what was prescribed. A fourth is ignoring needle dead space, which can shave a little from very small draws. Keep clean technique throughout: the CDC stresses a sterile, single-use needle and syringe for every injection (CDC, Safe Injection Practices). Never use oil that is cloudy, leaking, or past its discard date.

So, what does mg per week mean for testosterone?

mg per week is simply the total mass of testosterone delivered across seven days, regardless of how many injections you split it into. To convert it to a syringe volume, divide the per-injection mg by your vial's concentration in mg/mL, then multiply by 100 for U-100 units — for example, 100 mg on 200 mg/mL gives 0.50 mL (50 units). Use the testosterone (TRT) dose calculator to handle these conversions instantly for any dose and concentration.

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