Testosterone Injections vs Gel: Dosing Compared

Last updated: July 2026

Testosterone injections are dosed in milligrams per week and drawn as an exact volume in millilitres or U-100 syringe units, while testosterone gel is dosed as grams of gel or pump actuations applied to the skin daily — and only about 10% of what you apply is actually absorbed. That single difference is why an injection dose and a gel dose can never be matched milligram-for-milligram: 100 mg injected is not the same delivered dose as 100 mg of testosterone smeared on your shoulders.

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TL;DR — key takeaways

Different units entirely. Injections are measured in mg/week and read as units on a syringe; gel is measured in grams or pump presses applied per day.
Absorption is not 1:1. An intramuscular injection delivers essentially the full dose into the body; topical gel delivers only roughly 10% of what is applied across the skin.
Different serum shape. Injections give a peak-and-trough sawtooth every 7–14 days; daily gel gives a flatter, steadier level once it reaches steady state in 2–3 days.
Gel adds a transference risk. Testosterone can rub off onto partners and children from an unwashed application site — a caution injections do not carry.

Why the two dose scales cannot be matched directly

Depo-Testosterone (testosterone cypionate) is an oil depot injected into muscle. Once injected, the ester is slowly cleaved and nearly the entire milligram dose enters the circulation over the following days, with serum testosterone peaking about 2–3 days after the shot and then falling until the next one. Its labelled strengths are 100 mg/mL and 200 mg/mL, and its half-life when injected is roughly eight days — which is why weekly or twice-weekly dosing is common.

AndroGel is a topical hydroalcoholic gel. You apply it to clean, dry skin on the shoulders, upper arms, or abdomen, the alcohol evaporates, and testosterone diffuses through the skin over the next 24 hours. Only about 10% of the applied dose is absorbed systemically, so the number on the label (grams of gel, or milligrams of testosterone in the gel) is far larger than the amount that actually reaches your bloodstream. That is the crux: you cannot read across from "50 mg of gel" to "50 mg injected" because the delivered fractions are completely different.

Side-by-side: how each route is dosed

Property	Cypionate injection	Testosterone gel (AndroGel)
Route	Intramuscular oil depot	Topical / transdermal
Typical frequency	Every 7–14 days (often split weekly)	Once daily
Labelled strength	100 or 200 mg/mL	1% (50 mg / 5 g) or 1.62% (20.25 mg/pump)
Measured as	mL / units on a U-100 syringe	Grams of gel or pump actuations
Fraction delivered	~Full injected dose	~10% of applied dose
Serum profile	Peak-and-trough sawtooth	Steady once at steady state (~2–3 days)
Transference to others	None	Yes — from skin contact

Figures reflect the FDA-approved Depo-Testosterone and AndroGel labels. Your prescriber sets the actual dose, formulation, and monitoring plan; the arithmetic below only shows how each number is measured.

Two serum curves, same goal

The clearest way to see the difference is to plot serum testosterone over time. An injection climbs to a peak then drifts down to a trough before the next dose; a daily gel settles into a narrow band. Neither line is "better" on its own — they are two different shapes aiming at the same reference range.

Turning an injection dose into syringe units

For injections the maths is the same concentration arithmetic used across this site: divide the milligram dose by the vial concentration to get millilitres, then multiply by 100, because a U-100 syringe holds 100 units per mL.

Worked example 1 — 100 mg on 200 mg/mL

100 mg ÷ 200 mg/mL = 0.5 mL. 0.5 mL × 100 = 50 units on a U-100 syringe.

Worked example 2 — 200 mg on 200 mg/mL

200 mg ÷ 200 mg/mL = 1.0 mL. 1.0 mL × 100 = 100 units — a full 1 mL syringe.

Worked example 3 — same 100 mg on a weaker 100 mg/mL vial

100 mg ÷ 100 mg/mL = 1.0 mL = 100 units. Half the concentration means double the volume for the identical dose.

Worked example 4 — splitting 100 mg twice weekly

Two 50 mg shots per week from a 200 mg/mL vial: 50 mg ÷ 200 = 0.25 mL × 100 = 25 units each, keeping the weekly total at 100 mg.

How gel doses actually work out

Gel does not draw into a syringe, so there are no "units" — you count grams or pump presses, and then account for the roughly 10% that is absorbed. This is why gel milligrams look large next to injection milligrams.

Worked example 5 — AndroGel 1%, one 5 g packet

A 5 g packet of 1% gel contains 50 mg testosterone. At ~10% absorption, roughly 5 mg/day reaches the bloodstream — about 35 mg over a week, even though 350 mg was applied.

Worked example 6 — AndroGel 1.62%, two pumps

Each pump actuation delivers 20.25 mg; two pumps = 40.5 mg applied daily. At ~10% absorption that is roughly 4 mg/day delivered — a very different number from a 100 mg weekly injection that delivers close to 100 mg.

Cypionate dose-to-units reference chart

Common weekly injection doses shown as millilitres and U-100 units at both labelled strengths. Confirm against your own vial.

Weekly dose	On 100 mg/mL	On 200 mg/mL
50 mg	0.5 mL / 50 units	0.25 mL / 25 units
100 mg	1.0 mL / 100 units	0.5 mL / 50 units
140 mg	1.4 mL / 140 units	0.7 mL / 70 units
200 mg	2.0 mL / 200 units	1.0 mL / 100 units

Note that 200 mg on a 100 mg/mL vial needs 2.0 mL — more than a standard 1 mL syringe holds — which is one reason higher-strength vials or split doses are used for larger weekly amounts.

How this is calculated

Every injection figure uses two facts only: a U-100 syringe holds 100 units per mL, and concentration is dose divided by volume. The gel figures apply the label's approximate 10% transdermal absorption to the applied dose. There is no drug-specific constant and none of this is medical advice — it is the plain arithmetic behind a dose your prescriber has already chosen. The TRT calculator automates the injection side so you can check any draw against the chart above.

Frequently asked questions

Is 100 mg of gel the same as a 100 mg injection?

No. An intramuscular injection delivers close to the full milligram dose, while only about 10% of applied gel is absorbed. The two numbers describe applied amounts on different scales, not equal delivered doses.

Why is gel dosed daily but injections weekly?

Testosterone diffuses out of skin within about a day, so gel is reapplied daily to hold a steady level. Injected cypionate is an oil depot with a roughly eight-day half-life, so it releases slowly and is dosed every 7–14 days.

Do injections cause bigger swings than gel?

Generally yes. Injections produce a peak 2–3 days after the shot and a trough before the next one, whereas daily gel settles into a narrower band once at steady state. Splitting an injection into smaller, more frequent doses flattens the curve.

Can I switch from one to the other using the same number?

No — switching route is a prescriber decision with a fresh starting dose. Because delivered fractions differ so much, mapping your old milligram figure onto the new formulation would be misleading.

Sources

This guide is for general educational purposes only and does not constitute medical advice. Always follow your prescriber’s specific instructions and consult a qualified clinician before changing any protocol.