The previous post established that testosterone microdosing — smaller, more frequent doses — is pharmacokinetically superior to large infrequent bolus injections. What it left open was a more nuanced question: if you're committed to the microdosing principle, does it matter how you deliver those frequent small doses?
It does. Quite a bit, actually.
Subcutaneous Injection Microdosing: How It Works
Subcutaneous (SC) injection microdosing uses standard testosterone esters administered in small volumes into the fat layer beneath the skin, usually daily or every other day. The pharmacokinetic improvement over IM injection is genuine and measurable. Weekly 50 mg subcutaneous administrations maintain steady-state testosterone within the normal range while bypassing the supraphysiological peaks that characterize 200 mg IM protocols.
The limitation is the procedure itself. Daily subcutaneous injection requires needle preparation, accurate technique, sharps disposal, and a daily commitment to a medical procedure. Adherence data on self-injection protocols consistently shows compliance declining over time compared to topical application. A therapy measured in years is only as good as the adherence it generates.
The Polycythemia Gap
Injectable testosterone formulations — including subcutaneous microdosing protocols — are associated with the highest rates of elevated hematocrit among all TRT delivery methods. Daily transdermal formulations are associated with the lowest. The mechanism is consistent with the pharmacokinetics: even a well-managed SC microdosing protocol produces modestly higher peaks than daily transdermal application, and the erythropoietic response scales with peak level.
Daily Transdermal: The Original Microdosing Protocol
Daily transdermal testosterone is, in the most literal sense, the original clinical implementation of the microdosing principle. Applied once daily, it delivers a continuous low-level dose that maintains serum testosterone within the physiological range without producing meaningful peaks. The peak-to-trough variation for daily transdermal free testosterone is approximately 2.7 pg/mL — a number that barely registers as pharmacologically relevant. It is as close to a physiological steady state as current therapeutic options achieve.
The adherence profile of topical application outperforms self-injection across populations. Once-daily application to skin is cognitively equivalent to applying moisturizer — no needles, no sharps disposal, no technique degradation over time. Long-term adherence to daily transdermal testosterone is predictably stronger than long-term adherence to daily self-injection.
The Bioavailability Variable
The main pharmacokinetic caveat for transdermal testosterone is interindividual variability in absorption. Skin thickness, application site, humidity, and individual dermal characteristics all affect how much applied testosterone reaches the bloodstream. Approved gel formulations are dosed to deliver 10% bioavailability on average — which means a 50 mg application delivers approximately 5 mg systemically. But that average conceals real variation. Some patients absorb more efficiently; others absorb less. Dose titration based on serum monitoring is standard practice for transdermal TRT.
Which Is Better?
The honest clinical answer is that both approaches improve on traditional weekly IM injection, and the right choice depends on patient-specific factors. SC microdosing is useful for patients who prefer precise injectable dosing and are willing to sustain a daily injection routine. Daily transdermal is the better option for patients prioritizing adherence, minimizing polycythemia risk, and accessing the broadest long-term safety dataset. For the latter group — which is most patients — transdermal delivery does what microdosing promises to do, at a lower procedural burden, with more evidence behind it.
