How To Switch TRT Delivery Methods Safely: What To Know

Switching from one testosterone replacement therapy (TRT) formulation to another is common, but it isn't as simple as swapping products at the same dose. Each of the TRT delivery methods (injections, gels, creams, patches, oral capsules) absorbs differently, carries a distinct side-effect profile, and requires its own monitoring timeline. A safe switch starts with lab work, involves a provider-guided dose conversion, and includes follow-up bloodwork within weeks.

Marek Health supports men through formulation transitions with lab-based monitoring and individualized dosing. The Endocrine Society recommends individualizing TRT based on client factors, pharmacokinetics, and ongoing lab confirmation (Bhasin et al., 2018). For men exploring testosterone treatment options, understanding what each route involves and what a safe transition looks like is a practical first step.

TRT Delivery Methods Available Today

FDA-approved testosterone formulations for men with diagnosed hypogonadism include intramuscular injections (testosterone cypionate and enanthate), transdermal gels and patches, subcutaneous pellets, oral capsules (testosterone undecanoate), buccal tablets, and nasal gels. Compounded formulations (such as topical creams) are also prescribed but are not FDA-approved, and that distinction matters for labeling and safety claims. The AUA recommends commercially manufactured products over compounded versions when a suitable FDA-approved product exists (Mulhall et al., 2018).

The choice of formulation is a shared decision between the client and prescribing provider, based on individual clinical factors. The table below summarizes the major options.

Men comparing cypionate and enanthate esters or weighing oral testosterone against injections should discuss tradeoffs with their prescribing provider.

Why Do Men Switch TRT Delivery Methods?

Providers commonly see tolerability, side effects, and pharmacokinetic fit as the primary reasons men request a formulation change. No single route suits every client, and clinical experience suggests that formulation changes happen at least once for many men on long-term TRT.

Side Effects and Tolerability

Injection site pain, gel transference to partners or children, skin reactions from patches, and gum irritation from buccal tablets are all documented reasons men request a change. Erythrocytosis (elevated red blood cell concentration) is another driver. A 2025 retrospective study found that a substantial portion of men on TRT developed elevated hematocrit, with a smaller subset reaching levels at which guidelines recommend clinical intervention (Neidhart et al., 2025). Injectable esters, including cypionate and enanthate, appear to carry a higher rate of erythrocytosis than transdermal or oral formulations based on available observational data. Men managing hematocrit on TRT may switch routes specifically to reduce this risk.

How Do Pharmacokinetics Differ Between Formulations?

Transdermal gels and creams produce the smoothest pharmacokinetic curve, with the smallest gap between peak and trough levels at steady state. Intramuscular injections of cypionate or enanthate, dosed every one to two weeks, create larger swings that can exceed the range of normal diurnal variation. Some men report mood or energy fluctuations that coincide with peak-and-trough patterns, and a formulation change may reduce these symptoms in some cases.

Lifestyle and Convenience

Daily gel application requires skin contact precautions and consistent timing. Some men prefer the less frequent dosing of injections. These preferences are legitimate clinical considerations because poor adherence is associated with subtherapeutic levels and reduced symptom relief.

Bioavailability and Dose Conversion by Route

Bioavailability, the fraction of administered testosterone that reaches systemic circulation, varies by route. Injected testosterone (IM and subcutaneous) has the highest bioavailability. Transdermal gel has substantially lower bioavailability than injected testosterone, and the amount absorbed varies by product and application site (Wang et al., 2000). Oral testosterone undecanoate has lower bioavailability still, which is why oral doses are much higher than transdermal ones.

These differences mean that a dose conversion between routes is never a direct 1:1 translation. Providers use bioavailability estimates as a starting point, then titrate based on follow-up labs and symptom response. A man whose total and free testosterone levels were stable on injections will almost certainly need a different dose on gel or cream.

What Monitoring Is Needed After Switching?

Providers typically schedule follow-up labs within the first several weeks of a switch, with timing adjusted to the new formulation's pharmacokinetic profile. For transdermal products, levels are often drawn within the first two weeks. For injectable cypionate or enanthate, a trough level drawn just before the next injection gives a useful baseline.

Beyond testosterone itself, follow-up labs after a switch should include hematocrit, estradiol levels, and blood pressure. The Endocrine Society recommends monitoring hematocrit, PSA, and symptoms at regular intervals, with closer follow-up during formulation transitions (Bhasin et al., 2018). Blood pressure monitoring is now part of FDA labeling for all testosterone products following the 2025 update.

Does the Route of TRT Affect Hematocrit Risk?

Yes. Based on available observational data, short-acting injectable esters (cypionate, enanthate) appear to be associated with a higher rate of erythrocytosis compared to gels, patches, or longer-acting injectables like undecanoate. One hypothesis points to the high transient testosterone spikes from intramuscular injection, which may stimulate erythropoiesis more aggressively than the steadier levels produced by transdermal delivery.

For men whose hematocrit rises above guideline thresholds on injections, switching to a transdermal formulation is one option. The decision should be individualized, factoring in baseline hematocrit, body mass index (a predictor of erythrocytosis risk per Neidhart et al., 2025), and cardiovascular risk profile.

Cardiovascular Safety and the 2025 FDA Labeling Update

The TRAVERSE trial, a randomized, placebo-controlled study of 5,246 men aged 45-80 with hypogonadism and cardiovascular risk, found that transdermal testosterone was noninferior to placebo for major adverse cardiac events (7.0% vs. 7.3%; HR 0.96) (Lincoff et al., 2023). TRAVERSE enrolled men using transdermal gel; the FDA applied its labeling changes class-wide to all testosterone products, including injectables and oral formulations. The testosterone group did show higher incidence of atrial fibrillation and pulmonary embolism, findings that should not be overlooked.

In February 2025, the FDA issued class-wide labeling changes for all testosterone products (FDA, 2025). The agency removed the boxed cardiovascular warning, retained the Limitation of Use for age-related hypogonadism, and added a blood pressure warning based on ambulatory monitoring data. These changes apply regardless of formulation, so men switching between routes should understand that cardiovascular monitoring, including blood pressure, remains part of the standard of care.

Preparing for a Formulation Switch

Men considering a switch should discuss several points with their provider before making the change.

Fertility on TRT is one. Exogenous testosterone suppresses spermatogenesis. The degree of suppression varies, and recovery after stopping is not guaranteed and may take months. If fertility matters now or in the near future, adjunct therapies should be discussed before switching.

Product type is another. If the new formulation is compounded (a testosterone cream, for example), it is not FDA-approved. Compounded products are not the same as FDA-approved products in regulatory status, quality oversight, or labeling.

Men discontinuing TRT altogether, or switching in the context of sleep apnea or other comorbidities, need a plan that includes lab confirmation and symptom follow-up.

Safe switching of TRT delivery methods comes down to three things: a provider who knows the client's labs and history, a dose conversion grounded in bioavailability data, and follow-up monitoring timed to the new formulation, all guided by shared decision-making between the client and provider. Men on TRT through Marek Health can coordinate these steps with their care team.

Disclaimer: This blog post is intended for informational purposes only and should not be considered medical advice. Always consult a healthcare professional before making changes to your health routine.

FAQs

How do I safely switch from testosterone injections to gel?

Providers typically start the gel on the day the next injection would have been due, with dosing based on the individual's labs and clinical history. Dose adjustment is common because transdermal testosterone has substantially lower bioavailability than injected forms. This process requires lab monitoring and should not be attempted without clinical guidance.

Does switching TRT delivery methods affect fertility?

All exogenous testosterone suppresses sperm production to some degree, regardless of the delivery route. The suppression is variable across individuals. Recovery of spermatogenesis after stopping TRT is possible but not guaranteed, and the timeline ranges from months to over a year in some cases. Men who plan to have children should discuss this with their provider before switching or starting any formulation.

What monitoring is needed after changing TRT formulations?

At minimum, serum testosterone, hematocrit, and estradiol should be checked within the first few weeks after a switch, timed to the new route's pharmacokinetics. Blood pressure should also be monitored, per the 2025 FDA labeling update for all testosterone products. PSA and lipids are part of routine ongoing TRT monitoring as well.

Can switching TRT formulations lower hematocrit?

It may. Based on observational data, injectable cypionate and enanthate appear to be associated with a higher rate of erythrocytosis compared to transdermal formulations. Switching from injections to gel or cream is one strategy providers use to manage elevated hematocrit, though individual results vary.

Is a compounded testosterone cream the same as an FDA-approved gel?

No. Compounded testosterone products are not FDA-approved and do not undergo the same regulatory review as commercially manufactured formulations. The AUA recommends FDA-approved products over compounded versions when a suitable option is available. Compounded creams may be appropriate in specific clinical situations, but the distinction in regulatory status should be clearly understood.

How long does it take to reach stable levels after switching TRT routes?

It depends on the new formulation. Transdermal products typically approach steady state within one to two weeks. Injectable cypionate and enanthate may take several injection cycles (four to six weeks) to stabilize. Pellets release testosterone over three to six months with a more gradual absorption pattern. Providers confirm stable levels through follow-up lab work timed to each route's pharmacokinetic profile.

References

• J Clin Endocrinol Metab. 2018;103(5):1715-1744

• FDA class-wide labeling changes for testosterone products. Feb 28, 2025

• Front Endocrinol. 2025;15:1496906

• J Clin Endocrinol Metab. 2000;85(12):4500-4510

• J Urol. 2018;200(2):423-432

• N Engl J Med. 2023;389:107-117