Short answer: injectable testosterone cypionate means less-frequent dosing but a peak-and-trough pattern; topical gel/cream means steadier daily levels plus an FDA-documented risk of transferring the drug to others through skin contact.
If you're starting TRT, delivery method is one of the first real decisions you'll make — and injections and topical creams/gels behave quite differently in the body. Here's how absorption, dosing pattern, and documented side effects actually compare, based on FDA labeling and peer-reviewed pharmacokinetic data.
How Each One Is Absorbed
Testosterone cypionate is an ester — a modified, less-polar version of testosterone — that's injected into muscle in an oil-based solution. Because it's absorbed slowly out of that lipid depot, it doesn't need to be dosed daily; injections are typically spaced two to four weeks apart.[2] The FDA-approved label for testosterone cypionate lists an elimination half-life of roughly eight days after intramuscular injection, compared to just 10 to 100 minutes for free, unesterified testosterone circulating in the blood.[2]
After a single 200 mg injection, pharmacokinetic data show serum testosterone peaks at a mean of roughly 1,112 ng/dL around 4–5 days post-injection.[3]That creates a documented "peak-and-trough" pattern — levels run well above normal in the days right after an injection, then decline progressively toward near-baseline just before the next dose.[3]
Topical gel works differently. Designed for daily application, it produces steadier, more continuous serum concentrations without the pronounced peaks and troughs seen with injections — though absorption can still vary based on skin condition and where it's applied.[3]
The practical tradeoff:Injections mean fewer doses but more fluctuation in how you feel across the cycle. Topical products mean steadier levels but a daily routine — and a real, FDA-documented risk that doesn't exist with injections: transference to other people.
The Transference Risk Unique to Topical Testosterone
This is the most clinically significant risk that's specific to topical products. FDA-approved labeling for testosterone gel states plainly that the drug can transfer from a treated man's skin to other people through direct contact with unwashed or unclothed application sites.[5] FDA postmarketing surveillance has documented real cases of this causing virilization in children with secondary exposure — symptoms have included inappropriate genital enlargement, premature pubic hair development, increased erections, and aggressive behavior.[5]Women secondarily exposed to a partner's topical testosterone can experience virilizing signs like changed hair growth patterns and increased acne, and the labeling separately warns that a pregnant woman exposed to testosterone gel risks virilization of a female fetus.[5]
Because of this, FDA labeling explicitly instructs patients that children and women should avoid skin contact with unwashed or unclothed application sites, and that the product should be discontinued if signs of secondary exposure show up in anyone in the household.[5]This risk is manageable with basic precautions — covering the application site, washing hands after applying, letting it dry before contact — but it's worth knowing about upfront rather than discovering it after the fact.
Injectable testosterone doesn't carry this risk at all, since the drug goes directly into muscle rather than sitting on the skin surface.[1]
Side Effects by Delivery Method
Each method has its own side-effect profile, reflecting how differently they're absorbed.[4] Injectable testosterone is associated with injection site reactions, and a 2025 peer-reviewed dermatology review found injectable formulations generally carried higher rates of acne and systemic reactions compared to topical or oral testosterone.[4] Across all delivery methods, that same review found acne was the most commonly reported skin-related side effect, ranging from 0.6% to 9.1% of patients depending on formulation (lowest with oral), with itching affecting up to 10.0% and skin rashes up to 5.3%.[4]
For topical products specifically, an FDA-reviewed Phase 3 trial found application-site irritation was the most common skin-related event (seen in 12 patients), generally mild, with redness in 10 patients and acne in two — skin reactions were rarely severe enough to cause anyone to stop treatment.[7]
There's also a third option worth knowing about: subcutaneous testosterone pellets. They carry their own distinct set of insertion-related risks — polycythemia (elevated red blood cell count), bruising, and swelling at the insertion site — mechanistically different from either injections or topical products.[4]
The Bottom Line
Neither delivery method is objectively "better" — they're suited to different priorities. Injections mean less-frequent dosing but a peak-and-trough pattern in how you feel; topical products mean steadier daily levels but a real transference risk to manage and a daily routine to keep up with. What matters most is understanding the tradeoffs before you choose, and following the safety guidance that comes with whichever one you're prescribed.
Different TRT providers structure delivery-method options and pricing differently — start with what TRT is actually proven to help with, then compare providers on RENVA's Men's Health / TRT hub before you commit to one.
Sources
- Testosterone Cypionate Injection — Highlights of Prescribing Information — U.S. Food and Drug Administration accessdata.fda.gov
- Depo-Testosterone (testosterone cypionate injection) — Full Prescribing Information — U.S. Food and Drug Administration accessdata.fda.gov
- Pharmacokinetics of testosterone therapies in relation to diurnal rhythm and lifestyle — PMC (National Institutes of Health) pmc.ncbi.nlm.nih.gov
- Dermatological adverse effects of testosterone replacement therapy — Sexual Medicine Reviews (Oxford Academic) academic.oup.com
- Testosterone Gel, 1.62% — Full Prescribing Information — U.S. Food and Drug Administration accessdata.fda.gov
- Testosterone Gel — Full Prescribing Information — U.S. Food and Drug Administration accessdata.fda.gov
- Skin Reactions in a Phase 3 Study of a Testosterone Gel — PubMed (National Institutes of Health) pubmed.ncbi.nlm.nih.gov
Frequently Asked Questions
Can testosterone gel affect other people in my household?
Yes — this is a documented FDA-labeled risk. Testosterone gel can transfer through skin contact with unwashed application sites and has caused virilization in children and hormonal effects in women secondarily exposed.[5]
Why does injectable testosterone need less frequent dosing than gel?
Testosterone cypionate is absorbed slowly from an oil-based intramuscular depot, giving it an elimination half-life of about eight days — versus 10 to 100 minutes for unesterified testosterone — which is why it's typically dosed every two to four weeks rather than daily.[2]
Which delivery method has fewer side effects?
It depends on the type. Injectables tend to have higher rates of acne and systemic reactions, while topical products carry the transference risk and application-site irritation. Oral formulations had the lowest reported acne rates in one 2025 review.[4]
What is the "peak-and-trough" pattern with injections?
After an injection, testosterone levels rise well above normal within days, then decline progressively until the next dose — meaning the same person can be supraphysiologic shortly after injecting and near-baseline right before the next one.[3]