Testosterone

What testosterone does in the body

Testosterone is the main androgen, the group of hormones that drive the changes of a typically male puberty. Given as HRT, it raises your level into roughly the range a cisgender man's body would produce, and your body responds the way it would to any puberty: slowly, over years, with a lot of individual variation.

Once your level is high enough, the ovaries' own estrogen is largely overridden, which is why masculinizing HRT does not usually need a separate blocker. Periods stop for most people, and the estrogen-driven changes of the first puberty slow or reverse where they can. What changes, and when goes through the order.

Some of your testosterone is bound in the blood to a protein called SHBG and is not available to tissues. That is one reason two people on the same dose can end up with different results, and why prescribers look at blood tests rather than the dose alone.

Injections

Injections are the most widely used form worldwide. The two common short-acting versions are testosterone cypionate, which is what most US prescriptions are, and testosterone enanthate, more common in the UK, Europe and much of Asia. They behave very similarly. In the UK you may also meet Sustanon, a blend of several esters that release at different speeds.

Traditionally these are given into a muscle (intramuscular, or IM), in the thigh or buttock. Many prescribers now also use smaller injections under the skin (subcutaneous, or subQ) into the belly or thigh, with a shorter, finer needle that a lot of people find easier to do themselves. Evidence so far suggests subcutaneous injections give comparable levels for most people, but not every prescriber or pharmacy is set up for it, so ask.

The interval matters. A larger dose given less often, commonly every two weeks, gives a high peak a day or two after the injection and a low trough before the next one. Splitting the same total into smaller, more frequent injections, often weekly, gives a flatter line. People who feel great for the first week and flat, irritable or tired for the second are often describing that swing, and it is worth telling your prescriber rather than putting up with it.

Before your first self-injection

Ask your clinic to watch you do one, or to do the first one with you. Most clinics offer this, it takes ten minutes, and it is far easier to learn with someone checking your technique than from a video.

Long-acting injections

Testosterone undecanoate, sold in many countries as Nebido, is a long-acting injection given into a muscle, usually by a nurse, every few months once you are established on it. It is widely used in the UK's NHS and in parts of Europe, and less so in the US, where a related product exists but is restricted.

Its big advantage is steadiness. After the first few loading injections, levels stay much flatter than with short-acting injections, and you are not doing anything at home. The downsides are that it is a large, oily injection that some people find painful, it takes a while to adjust if your levels run high or low, and missing an appointment has a long tail. Some people start on it; others move to it once they know how they respond.

Gels and patches

Transdermal testosterone goes through the skin. Gels are the most common: rubbed onto the shoulders, upper arms, belly or thighs once a day. Brands vary by country, with Testogel and Tostran common in the UK. Patches exist too, and are used less, partly because many people find they irritate the skin.

Daily gel gives the steadiest levels of any common form, with no peak and trough in the injection sense, which some people strongly prefer. It suits people who hate needles. The trade-offs are the daily routine, and transfer: gel on your skin can rub off onto a partner, child or pet through contact, so you let it dry, wash your hands and keep the area covered. Absorption also varies between people, and some find it hard to reach the level they want on gel alone.

If you use gel and live with others

Pick one application site and one time of day, usually after a morning shower, and keep that area under clothing. It makes the routine automatic and cuts the risk of anyone else absorbing it.

Pellets

Testosterone pellets are small implants placed under the skin, usually in the hip area, in a short procedure under local anaesthetic. They release slowly over a few months. They are mainly offered in the US, and fewer gender-affirming prescribers use them.

The appeal is not having to think about it. The drawbacks are that once pellets are in, the dose cannot easily be lowered, levels drift down towards the end, and occasionally a pellet works its way out or the site gets infected. They are more often something people move to once they are stable than where they start.

How people choose

In practice the choice is often made for you, at least at first, by what your prescriber, health system or insurer offers. Within that, the things people weigh are:

• Needles or not. Gel and patches avoid them; long-acting injections keep them to a clinic visit every few months.
• Steadiness. Gel and long-acting injections are flattest; fortnightly short-acting injections swing the most.
• Routine. Daily gel versus a weekly or fortnightly injection versus a nurse appointment every few months.
• Cost and supply. Prices differ hugely by country and by form, and there are periodic shortages of specific products. Cost and insurance covers what people pay.
• Upcoming surgery. Some surgeons ask about your form of testosterone before an operation. Hormones and surgery explains why.

Switching forms is common and not a failure. Plenty of people start on one, notice the swings or the routine does not suit them, and change after a conversation and a blood test.

Blood levels and what they are aiming for

Your prescriber adjusts the dose to your blood results and how you feel, not to a fixed number. Guidelines aim for testosterone in roughly the typical adult male range, and how the level is measured matters as much as the number: with injections, a sample drawn the day after gives a peak and one drawn just before the next dose gives a trough, and the two can be far apart.

How to read your hormone blood results gives the ranges guidelines cite in both units and explains the timing. Blood tests and monitoring covers what else is checked, including hematocrit, and how often.

If you take testosterone without a prescription, get the blood tests anyway and get into a clinic when you can; many will take on someone already taking hormones without judgement.

Frequently asked questions

Which form of testosterone is best?

There is no single best. Gel and long-acting injections give the steadiest levels; short-acting injections are cheap and widely available; the right one is the one you can take reliably. See how people choose.

Are subcutaneous injections as good as intramuscular?

For most people they seem to give comparable levels with a smaller needle, though not every prescriber offers them. See injections.

Why do I feel worse the week before my injection?

Often it is the trough, the low point before the next dose. Telling your prescriber is worth it, because a shorter interval or a different form can flatten the swing. See injections.

Can testosterone gel affect other people?

Yes, through skin contact before it has dried or if the area is uncovered. Let it dry, wash your hands and keep it covered. See gels and patches.