Gel or injection? choosing the right testosterone

Testosterone can be replaced through the skin, into muscle, or under the skin, and the delivery route shapes almost everything about the experience. Transdermal gels are rubbed onto the shoulders or upper arms once a day; roughly 10% of the applied dose is absorbed, producing stable blood levels that track the body's own daily pattern. Short-acting intramuscular esters — testosterone cypionate and enanthate — are injected every one to two weeks and produce a sharp rise followed by a slow fall. Long-acting intramuscular testosterone undecanoate is given roughly every ten weeks and holds levels remarkably flat, but must be administered in a medical setting because of a rare risk of a serious reaction. Subcutaneous injection — a small needle into the fat, often weekly — has become popular because it is easy to self-administer and produces steadier levels than the classic deep intramuscular shot.^[2]

The single biggest difference between gels and short-acting injections is the shape of the curve. A cypionate or enanthate injection pushes testosterone to a peak — often above the normal range — within a day or two, then lets it drift down to a trough before the next dose. Many men feel that arc: good in the first days, flat and irritable by the end. A daily gel, by contrast, holds a steady plateau within the normal range. Neither is inherently "right," but the swing matters for how you feel and for side effects that track the peaks.^[2]

Testosterone stimulates the bone marrow to make red blood cells, and if the haematocrit climbs too high the blood thickens and clotting risk rises. This is where delivery route matters most. Short-acting intramuscular injections, with their supraphysiologic peaks, carry by far the highest risk: across reviews, roughly 40% of men on intramuscular testosterone develop erythrocytosis, compared with only about 3% on transdermal gel.^[1] Long-acting and subcutaneous injections sit between the two. It is the reason clinicians check a haematocrit before starting and periodically after, and pause or switch treatment if it climbs above 54%.^[3] A baseline blood panel before starting therapy makes that monitoring straightforward.

Gels carry a risk injections do not: the testosterone sits on the skin and can rub off onto someone else. Documented skin-to-skin transfer has raised testosterone levels in female partners and caused signs of early puberty and virilization in children — which is why every testosterone gel in the United States carries a boxed warning about secondary exposure.^[3][5] The risk is manageable: apply to areas covered by clothing, wash hands immediately, let it dry, and avoid skin contact at the application site until it has been washed. But for a man with young children at home, it is a genuine consideration that can tip the decision toward an injection.^[5]

Beyond the biology, daily life decides a lot. Gels are effortless to apply but must be remembered every single day, cost more as brand-name products, and come with the transference precautions. Short-acting injections are inexpensive — often the cheapest option by far — and only needed weekly or fortnightly, but require comfort with a needle and bring the peak-and-trough swing. Long-acting injections mean just a handful of visits a year but tie you to a clinic for each dose. Subcutaneous injection has become many men's sweet spot: cheap, steady, and easy to self-administer at home.

Whichever route you choose, the follow-up looks similar — a repeat testosterone level and a haematocrit, read alongside the rest of your hormone panel.