Testosterone, Explained: The Forms, The Routes, And Why We Use Daily Microdosing

Introduction

If you've been reading about testosterone replacement therapy, usually called TRT, you've probably noticed something strange. Every clinic uses the word "testosterone" as if there is one thing in the bottle. There are several forms of testosterone, several ways to put it into the body, and the choice between them changes how you feel and what happens to your labs.

This is the piece most men wish a clinic had given them before they were ever started on testosterone. It walks through the forms, the routes, and the reason we land on daily subcutaneous microdosing for the men we treat.

I'll tell you what we know, where the evidence is thinner, and where the studies point.

The hormone, and why the form matters

Testosterone is a steroid hormone your testes make every day. Pure testosterone, by itself, does not sit well in an injection. It clears the body in a few hours. That is why pharmaceutical companies took the testosterone molecule and chemically attached a fatty acid chain called an ester to slow how fast it releases from the injection site.

The ester does not change what testosterone does in your body. It changes how quickly the testosterone becomes available after you inject it. A short ester releases fast. A long ester releases slowly. The hormone you end up with in your bloodstream is identical in either case. The release curve is what is different.

That release curve is the whole conversation. It determines whether your blood level is steady or whether it spikes and crashes.

The forms

Here are the forms a US physician is most likely to prescribe, with the half-life and what that means for dosing rhythm.

Testosterone propionate is a short ester. Its half-life is around 0.8 days. It has to be injected every other day or so to keep levels even. Almost no clinic in the United States uses this for testosterone replacement therapy anymore because the dosing is too frequent for most patients to tolerate long term.

Testosterone enanthate is a medium-long ester. Its half-life is around 4.5 days. It is a standard weekly injection. It is also available as a brand-name autoinjector for subcutaneous use called Xyosted.

Testosterone cypionate is a medium-long ester. Its half-life is around 8 days. This is the most commonly prescribed injectable testosterone in the United States. It is usually given as a weekly intramuscular shot, though it can also be given subcutaneously.

Testosterone undecanoate is a long ester. The injectable version, Aveed or Nebido, is dosed every 10 weeks after a loading phase. The oral version, Jatenzo, Kyzatrex, or Tlando, is a capsule you swallow twice a day with food. According to PubMed, the oral form uses a special absorption pathway through the lymphatic system to bypass first-pass metabolism through the liver, which earlier oral testosterone forms could not do safely (Campbell 2023, DOI).

Testosterone suspension has no ester. It is pure crystalline testosterone in water. It is used almost exclusively by bodybuilders. It is not a normally prescribed product.

These are the building blocks. The next question is how testosterone gets into your body.

The routes of administration

You can give testosterone several different ways. Each one has a trade-off.

Intramuscular injection, usually called IM, is the classic route. A 1-inch or 1.5-inch needle goes into the muscle of the thigh, glute, or shoulder. The common protocol is 100 to 200 mg of testosterone cypionate once a week.

What patients feel on weekly IM dosing is often a peak in mood and energy a few days after the shot, then a noticeable drop in the day or two before the next one. This is the rollercoaster patients describe when they say a clinic put them on weekly testosterone and they could not tell if it was working.

What the labs show is the same pattern. Weekly IM dosing produces supraphysiological testosterone peaks, meaning levels well above what a healthy young man would naturally produce, followed by troughs that can fall below baseline before the next dose (Choi 2021, DOI). Those peaks are the engine behind the 2 main side effects men worry about, rising estradiol and rising hematocrit. Estradiol is the estrogen that testosterone gets converted into. Hematocrit is the percentage of red blood cells in your blood.

Subcutaneous injection, usually called SC or subq, uses a short, fine insulin-type needle, typically 27 to 31 gauge and 1/2 inch, into the fatty layer just under the skin of the belly or thigh. The injection itself takes seconds. Most patients say it does not hurt much.

According to PubMed, when researchers compared subcutaneous to intramuscular testosterone in the same patients, both routes produced similar total testosterone exposure, but the subcutaneous route had less pain, less pre-injection anxiety, and was preferred by the patients who tried both (Wilson 2018, DOI; Spratt 2017, DOI).

The clinical advantage shows up in safety markers. In a study of 234 men with low testosterone, the subcutaneous group ended up with significantly lower estradiol levels and lower hematocrit at 12 weeks compared to the intramuscular group, despite reaching similar total testosterone (Choi 2021, DOI). The hormone is identical. The delivery is steadier, and you end up with fewer side effects to manage.

Transdermal testosterone includes gels, creams, and patches. You rub it on your shoulders, upper arms, or abdomen in the morning. Brand-name gels include AndroGel, Testim, Fortesta, and Axiron.

The upside is no needles. Daily dosing keeps levels relatively steady. The downside is variable absorption. Some men absorb it well. Some do not. A 2015 review found that secondary transfer to a partner or child through skin contact is a documented risk, which is why the FDA requires a boxed warning on these products (Hadgraft 2015, DOI). You also have to wait before showering or sweating heavily, and you need to avoid skin transfer during the first several hours after application.

Oral testosterone undecanoate capsules are a more recent option. Brand names include Jatenzo, Kyzatrex, and Tlando. They are taken twice daily with a fat-containing meal.

According to PubMed, a phase 3 trial in 315 hypogonadal men showed that 87% reached a normal testosterone range on twice-daily oral testosterone undecanoate, and the safety profile was comparable to a testosterone gel (Miner 2024, DOI). The upside is no needles and no skin transfer risk. The downside is that absorption requires a meal with adequate fat, levels can still swing within the day, and cost is generally higher than injection.

Nasal testosterone, sold as Natesto, is a gel pumped into each nostril 3 times a day. The selling point is that nasal absorption produces brief peaks that may not suppress the brain's signal to the testes as aggressively as injections do, so men trying to preserve fertility sometimes prefer it. The limitations are obvious. Three doses a day, nasal irritation for some men, and variable coverage or pharmacy access. We do not use it routinely.

Pellets are subcutaneous implants. A physician makes a small incision in the upper hip area, slides 8 to 12 testosterone pellets the size of a grain of rice into the fat layer, and closes it. The pellets release testosterone over roughly 3 to 6 months.

According to PubMed, a phase IV study showed pellets normalized testosterone in hypogonadal men over a 3 to 6 month window (Kaminetsky 2011, DOI). The upside is that no daily or weekly action is required. The downside is that it is a minor surgical procedure, you cannot lower the dose if you do not like how it feels, there is a small risk of pellet extrusion or infection, and the cost per insertion is significant.

Buccal tablets, such as Striant, adhere to the gum and release testosterone through the cheek lining over 12 hours. They require twice-daily dosing. Most patients dislike the feel and the taste. They are rarely prescribed today.

The peak-and-trough problem

Here is the part that matters more than the brand on the bottle.

Your testes do not dump out a week's worth of testosterone on Monday morning and then take 6 days off. A healthy young man produces testosterone in pulses across the day, with the highest level in the morning and a gradual decline by evening. His levels move within a band. They do not spike and crash.

A weekly intramuscular shot does not do this. It loads a high dose into the muscle, the ester slowly releases it, and the blood level rises to a peak around days 2 to 4, then falls toward a trough by day 7. Some men describe it as feeling on early in the week and off before the next shot.

That peak-and-trough pattern has 2 clinical consequences.

First, higher estradiol. When testosterone levels spike, more of it gets converted to estradiol by an enzyme called aromatase. Estradiol matters for bone, brain, and cardiovascular health, but men with very high estradiol can develop water retention, mood swings, and breast tenderness. Subcutaneous dosing produces lower peaks and therefore lower estradiol on average than intramuscular dosing (Choi 2021, DOI).

Second, higher hematocrit. Testosterone stimulates red blood cell production. Big peaks drive bigger increases in hematocrit. Hematocrit above 52 to 54% gets into a range where blood thickens and clot risk rises. This is the single most common reason a testosterone replacement patient has to pause therapy or donate blood. Again, subcutaneous patients in the Choi study had significantly lower hematocrit at 12 weeks than the intramuscular group.

So the same total dose, delivered with a flatter curve, can produce fewer of the side effects that scare men away from testosterone therapy.

Why we use daily subcutaneous microdosing

Most testosterone clinics give a single weekly intramuscular shot because it is the path of least resistance. One injection per week, one bottle, one line on the prescription. The pharmaceutical labels were written that way decades ago and the protocol got copied across the industry.

We do it differently. Patients on our protocol inject a small dose of testosterone cypionate subcutaneously every day, or every other day, using an insulin-type syringe. The total weekly dose could be the same a typical clinic might use. We find that most patients feel better on a lower total dose.

I have friends who have been on 200 mg IM once a week for years. They feel the trough before it is time for reinjection and they are ready on day 7. Microdosing rarely gets to that total dose in 7 days. The delivery is broken into 7 small pieces instead of 1 large one.

The first reason is a flatter curve. Daily microdosing brings the peak-to-trough ratio close to 1, which means your level on a Tuesday afternoon looks a lot like your level on a Saturday morning. This is closer to what your body produced when it was making its own testosterone.

The second reason is lower estradiol pressure. Lower peaks mean less aromatization. Many of our patients never need an aromatase inhibitor, which is a separate medication a lot of weekly-IM clinics add by default.

The third reason is lower hematocrit drift. Same dose, smaller spikes, less stimulus to overproduce red cells. Fewer patients run into the too-thick problem that forces a dose cut.

The fourth reason is that the subq route itself is gentler. A short, fine needle into the fat layer hurts less and bruises less than a 1.5-inch needle into the muscle, and the studies show patient preference for subq is strong once men try it (Wilson 2018, DOI; Spratt 2017, DOI).

The fifth reason is better symptom stability. Patients consistently report they do not feel the weekly cycle of good days and bad days that they got on weekly intramuscular dosing.

What this looks like in practice is a small insulin syringe, a tiny volume of medication, and a 10-second injection into the belly fat after morning coffee. Most patients say within a week or two they do not think much about it. It becomes like brushing your teeth.

The honest caveats

A few things need to be said before a patient signs anything.

The evidence base for daily microdosing is mostly clinical, not large randomized trials. The published studies that exist on subcutaneous testosterone use weekly subq, not daily subq. Daily microdosing is the logical extension of that evidence combined with what we know about endogenous testosterone rhythms. It is how a lot of experienced testosterone physicians have moved over the last several years. It is not the protocol the average urology textbook describes.

Daily subq is not right for every patient. Some men do fine on weekly intramuscular. Some have a fear of needles and would rather wear a gel. Some want pellets because they do not want to think about therapy for 4 months. Those are different trade-offs, and they can be reasonable in the right context.

Testosterone replacement therapy is a long-term medication. Once you start, your body downregulates its own production. If you stop, your levels fall to wherever they were before, sometimes lower for a period of months. This is true on every form and every route. Anyone telling you otherwise is selling you something.

The right protocol starts with the right diagnosis. We do not prescribe testosterone because a man wants more energy. We prescribe it after a 100+ biomarker workup confirms that testosterone deficiency is the actual problem and other causes have been ruled out. If you are not a candidate, we will tell you. That gate is the most important part of the protocol, regardless of which form or route comes after it.

How to use this

If you are reading this while evaluating a clinic, these are the questions worth asking.

Which form of testosterone are you prescribing? You want a specific answer.

Which route? Intramuscular, subcutaneous, gel, oral, pellet, nasal, or another route.

How often? Weekly, every other day, or daily.

How are you monitoring estradiol and hematocrit? What is the plan if they rise?

Did a physician review my labs before the first call? Before the call, with enough time to actually read them.

A good clinic will answer those questions without hedging. If the answers are vague, or if testosterone is testosterone is the answer you get, that tells you what you need to know.

If you want to see how Sage Matters handles this process, start with the testosterone assessment or read about our testosterone therapy service.