How Long Do Testosterone Shots Last?

How long a testosterone shot lasts depends on which formulation you receive. The most commonly prescribed injectable esters, testosterone cypionate and testosterone enanthate, maintain meaningful blood levels for roughly one to two weeks per injection. Testosterone undecanoate, a long-acting depot formulation, can stretch that window to about ten to twelve weeks. But the question “how long does it last” has layers beyond the raw pharmacokinetics, because the way you feel across a dosing cycle, how quickly benefits accumulate, and what happens when you stop all operate on different timelines.

Cypionate and Enanthate, the Workhorses

Testosterone cypionate and testosterone enanthate are the formulations most people encounter when starting injectable testosterone replacement therapy. Both are dissolved in oil and injected into muscle (or, increasingly, under the skin). After injection, the ester slowly cleaves from the testosterone molecule, releasing active hormone into the bloodstream over days. The pharmacokinetic profiles of these two esters are similar enough that clinicians often treat them interchangeably.

A typical dosing schedule for either ester is every one to two weeks, though many prescribers now favor smaller doses given weekly or even twice weekly to keep blood levels more stable. Larger doses spaced further apart produce a sharper spike in testosterone within the first few days, followed by a gradual decline that can dip below the therapeutic range before the next injection is due. That rise-and-fall pattern is the central limitation of these formulations and the reason dosing frequency has shifted over time.

Testosterone Undecanoate, the Long-Acting Option

Testosterone undecanoate (sold as Nebido or Aveed, depending on where you live) is a much longer-acting ester. The undecanoate side chain is larger, which slows the release of active testosterone from the oil depot considerably. In a study tracking hypogonadal and transgender men on this formulation, the median optimal injection interval settled at 12 weeks, with most patients falling in a range of about 10 to 13 weeks between shots.¹ Age and body size influenced the interval: larger or older patients sometimes needed slightly shorter gaps between injections.

That 10-to-13-week range is a huge practical advantage for people who dislike frequent needles. The tradeoff is a longer loading period at the start of treatment (the first two injections are typically given closer together, around six weeks apart, before settling into the longer schedule) and the fact that if you do have side effects, the drug clears your system more slowly. Washout after discontinuation of testosterone undecanoate can be surprisingly prolonged, something worth keeping in mind if fertility is a concern or if treatment needs to be paused quickly.

Testosterone Propionate and Other Short-Lived Esters

On the opposite end of the spectrum, testosterone propionate has a terminal half-life of roughly 19 hours, meaning it leaves the body fast. To maintain therapeutic levels, injections need to happen every two to three days.² That frequency makes propionate impractical for most people on long-term replacement therapy, and it is rarely prescribed for that purpose today. It still shows up in some clinical settings and in compounding pharmacies, and it has been studied as a potentially more fertility-friendly option compared to longer-acting formulations. In animal models, short-acting testosterone had less of a suppressive effect on the hormonal signals that drive sperm production than long-acting depot testosterone did.²

The Peak-and-Trough Problem

The duration of a single shot is only part of the picture. What many people actually want to know is: how long will I feel good after each injection? For cypionate and enanthate given at standard intervals, blood testosterone typically peaks within a day or two and then declines steadily. When larger doses are given at longer intervals, the swings between peak and trough can be pronounced enough to produce noticeable symptoms on both ends of the cycle.³

In the days after a shot, when levels are at their highest, some people report elevated energy and mood but also irritability, oily skin, or restlessness. As levels fall in the days before the next injection, symptoms of low testosterone can creep back: fatigue, low mood, and reduced libido. Research on hormone therapy in transgender men has documented this pattern clearly, with mood elevation and increased energy during the peak phase giving way to mood swings and depressive symptoms as the trough approaches.⁴

This roller coaster is one of the main reasons clinicians have moved toward more frequent, smaller injections. Splitting a biweekly dose into two weekly doses, or even three doses spread across the week, flattens the curve. The total amount of testosterone delivered stays roughly the same, but the peaks are lower and the troughs are higher, which for many people translates into more consistent energy and mood throughout the week.

Does It Matter Whether You Inject Into Muscle or Under the Skin?

Intramuscular injection has been the default route for decades, but subcutaneous injection has gained traction as a less painful alternative. The evidence so far suggests that when you give the same dose of the same ester, the two routes produce comparable overall testosterone exposure.⁵ A pilot study comparing the two routes in gender-affirming therapy found no meaningful difference in total testosterone exposure.⁶

There are subtle kinetic differences, though. With subcutaneous testosterone undecanoate, peak testosterone concentration arrives later, around eight days after injection versus about three days with intramuscular delivery.⁷ That slower rise could mean a slightly smoother ride for people sensitive to post-injection spikes, though the overall peak concentration and the time the drug spends in the body did not differ between routes in that same study. For most people, the practical effect is that subcutaneous injection works about as well and hurts less, which makes it easier to stick with a frequent dosing schedule.

How Long Until the Benefits Show Up

Even though a shot of testosterone reaches your bloodstream within hours, the clinical effects accumulate over weeks and months. The timeline varies by which symptom you are tracking. Improvements in depressive mood tend to appear within three to six weeks and reach their maximum somewhere between 18 and 30 weeks of treatment.⁸ Sexual desire often picks up earlier, while changes in body composition take longer to become visible.

A study following 161 men with late-onset hypogonadism on long-acting testosterone undecanoate found that waist circumference and body fat percentage both decreased over the course of treatment, total and LDL cholesterol dropped, and erectile function scores improved.⁹ These changes did not happen after a single injection; they developed cumulatively over months. The point is worth emphasizing because people sometimes judge whether testosterone “is working” based on how they feel a few days after the first shot, which mostly reflects the pharmacokinetic spike, not the therapeutic benefit they are after.

Side Effects and How Quickly They Develop

Some side effects track closely with the peak-and-trough cycle. Acne and oily skin tend to flare when levels are highest, while fatigue and irritability may worsen near the trough. Other side effects accumulate gradually, more like the benefits do.

A good example is the effect on red blood cell production. Testosterone stimulates the bone marrow to produce more red blood cells, which raises hematocrit (the percentage of your blood made up of red cells). In a randomized trial comparing intramuscular testosterone cypionate to intranasal testosterone gel, men on injections saw their mean hematocrit climb from about 43% to nearly 47% after four months of treatment, while the gel group showed no significant change.¹⁰ That rise matters because excessively high hematocrit thickens the blood and increases cardiovascular risk, which is why regular blood work is standard practice during testosterone therapy. The hematocrit effect is thought to be driven partly by the supraphysiologic peaks that injectable testosterone produces, which is another argument for the lower, more frequent dosing strategy.

What Happens When You Stop

If you stop injections, blood testosterone levels will eventually fall back toward whatever your body was producing on its own. How quickly that happens depends on the ester. With cypionate or enanthate, levels decline meaningfully within a week or two. With testosterone undecanoate, the clearance is slower and can extend well beyond what the labeled half-life might suggest. Case reports have documented an unexpectedly prolonged washout in some men after discontinuing testosterone undecanoate injections, with exogenous testosterone remaining detectable for longer than anticipated.

The bigger question most people have is whether their body’s own testosterone production will bounce back. Exogenous testosterone suppresses the hormonal signals from the brain (LH and FSH) that tell the testes to make testosterone and sperm. When you stop, those signals need to recover. In a study of men recovering after androgenic steroid use, about 80% had satisfactory recovery of testosterone levels by three months, with LH rising back to normal ranges. But roughly one in five still had testosterone below the low end of normal at that point.¹¹ The strongest predictors of poor recovery were how long the person had been on testosterone, the dose used, and the type of preparation. The longer and heavier the use, the slower and less complete the recovery.

Not everyone rebounds, and some men experience uncomfortable symptoms of low testosterone during the recovery period that can take months to resolve.¹² Clinicians sometimes use medications like clomiphene or hCG to help jumpstart the body’s own production during this transition, rather than leaving patients to ride it out unassisted.

Why the Same Shot Lasts Differently in Different People

Even on identical doses of the same formulation, two people can have noticeably different experiences of how long a shot “lasts” in terms of symptom relief. Several factors drive this variation.

Body composition is one of the more underappreciated ones. Testosterone is lipophilic, meaning it dissolves readily into fat tissue, and higher body fat is associated with lower circulating testosterone. Research has shown that testosterone levels decrease substantially with each percentage-point increase in total body fat.¹³ In practical terms, this means a person with more body fat may metabolize or sequester injected testosterone differently, potentially shortening the effective window of each shot. The optimal injection interval data for testosterone undecanoate specifically noted that body surface area influenced how often patients needed their next dose, with larger individuals trending toward shorter intervals.¹

Age plays a role too. Sex hormone-binding globulin, the protein in blood that binds testosterone and keeps it inactive, tends to rise with age. Higher binding means less free testosterone available to act on tissues, which can make the tail end of a dosing cycle feel more symptomatic in older patients even if their total testosterone numbers look acceptable on paper. The interplay between injection pharmacokinetics and individual biology is why good testosterone management typically involves periodic blood draws timed at both peak and trough, not just a single measurement.

The Oil Matters More Than You’d Think

An oddity of injectable testosterone that rarely gets discussed outside pharmacology is that the carrier oil influences how long the drug stays active. Testosterone esters are dissolved in oil, and the composition of that oil affects the rate at which the drug depot disperses from the injection site. Early research comparing testosterone dissolved in standard oil versus hydrogenated soybean oil found a dramatic difference in duration of action: testosterone was undetectable in the blood within five days when given in conventional oil, whereas the same testosterone in hydrogenated soybean oil maintained physiologic blood levels throughout the entire study period.¹⁴

Different commercial products use different oils (cottonseed oil, sesame oil, castor oil, or grapeseed oil are all common), and switching brands can occasionally change how a patient experiences the same nominal dose and ester. If you notice a shift in how you feel after a pharmacy switches your product to a different manufacturer, the oil vehicle is a plausible explanation worth mentioning to your prescriber.

Fertility Considerations and Timing

One of the most consequential “how long does it last” questions involves fertility. Exogenous testosterone suppresses sperm production, sometimes profoundly. This suppression begins within weeks of starting therapy and can persist well after stopping, as discussed in the recovery section above. For men who want to preserve the option of fathering children, the choice of formulation and the duration of use both matter.

Animal data suggests that short-acting formulations like testosterone propionate may suppress the reproductive axis less severely than long-acting depot formulations. Mice given propionate returned to fertility faster and had less dramatic suppression of LH compared to those given long-acting pellets.² Whether that finding translates cleanly to humans is not settled, but the principle makes pharmacologic sense: shorter exposure windows give the brain’s signaling system more opportunity to recover between doses. This is one reason why some fertility-minded protocols use very short-acting testosterone or avoid exogenous testosterone altogether, substituting medications that boost the body’s own production instead.

The recovery data from human studies reinforces caution. Duration of testosterone use was the strongest predictor of how well the hormonal axis recovered, with longer use linked to slower and less complete rebounds.¹¹ If preserving fertility is important to you, that conversation needs to happen before starting testosterone, not after months or years of suppression.

Picking a Dosing Schedule That Fits Your Life

The range of options spans from every-other-day propionate injections on one end to a quarterly clinic visit for testosterone undecanoate on the other. Most people on replacement therapy end up somewhere in the middle, doing weekly or biweekly cypionate or enanthate injections at home. The “right” frequency is less about pharmacology in the abstract and more about which schedule keeps your levels stable enough to feel good while fitting into your routine.

If you are new to testosterone therapy, it is reasonable to start with a standard protocol and then adjust based on blood work and symptoms. Trough blood draws, taken the morning before your next scheduled injection, are the most useful for fine-tuning. If trough levels are low and you feel it, the options are to increase the dose, shorten the interval, or both. Many patients end up on a slightly different schedule than the one they started with, which is normal and expected rather than a sign that something is wrong. The pharmacokinetics give you a framework, but the schedule that actually works is the one that keeps you feeling steady.