Testosterone cypionate has a half-life of approximately eight days when injected into muscle, meaning half the dose is still active in your body about a week after injection. A single shot typically keeps testosterone levels elevated for roughly two weeks before dropping below the therapeutic range, which is why most prescribing schedules call for injections every one to two weeks. But “how long it lasts” depends on what you’re really asking: how long it works, how long until you need another shot, or how long it stays detectable in your system.
Half-Life and How It Works in Your Body
Testosterone cypionate is dissolved in oil and injected deep into muscle tissue, where it forms a slow-release depot. The cypionate ester attached to the testosterone molecule controls how quickly your body breaks it down and releases active testosterone into your bloodstream. With an eight-day half-life, roughly half the injected dose remains at the injection site after one week. After two half-lives (about 16 days), a quarter remains. After three half-lives (about 24 days), an eighth is left.
This gradual release creates a predictable rise-and-fall pattern. Testosterone levels peak within the first few days after injection, then steadily decline. By the end of two weeks, levels have dropped significantly, which is why many people notice symptoms returning near the end of a standard dosing cycle.
Typical Injection Schedules
The Endocrine Society’s clinical practice guideline recommends testosterone cypionate at 150 to 200 mg injected every two weeks, or 75 to 100 mg weekly. The goal is to keep blood testosterone in the mid-normal range for healthy young men, generally between 350 and 600 ng/dL at the midpoint between injections.
The every-two-week schedule is the most commonly prescribed starting point, but it creates wider swings between peaks and troughs. In the first few days after a shot, levels climb well above baseline. By day 12 to 14, they may dip low enough that fatigue, mood changes, or low energy creep back in. Weekly injections at a lower dose smooth out these peaks and valleys, keeping levels more stable throughout the cycle. Some men on testosterone replacement therapy split their dose even further, injecting smaller amounts twice per week to minimize fluctuations.
Your doctor should check your testosterone level midway between injections. If that mid-interval reading comes back above 600 ng/dL, the dose or frequency needs to come down. If it’s below 350 ng/dL, you likely need a higher dose or more frequent injections.
How Long It Stays Detectable
Detection is a separate question from how long you feel the effects. Testosterone cypionate remains in your system well beyond the point where it stops meaningfully raising your levels. The FDA used a washout period of at least 70 days (10 weeks) between treatment periods in clinical studies of testosterone cypionate, which gives a rough sense of how long traces can linger.
For athletic drug testing, detection windows vary by the specific testosterone ester. Longer-acting esters are generally detectable for longer periods. Closely related esters like testosterone decanoate have shown detection times of about 18 days in blood, while testosterone undecanoate (the longest-acting ester) has been detected for at least 60 days. Testosterone cypionate falls somewhere in this range, though exact detection times depend on the dose, number of prior injections, individual metabolism, and the sensitivity of the test being used. Standard anti-doping tests measure the ratio of testosterone to a related hormone in urine, and abnormal ratios can persist for weeks after the last injection.
What Affects How Long Each Shot Lasts
Several factors influence how quickly your body processes each injection. Body composition plays a role: people with higher body fat percentages tend to convert more testosterone into estrogen through a process called aromatization, which can effectively shorten how long usable testosterone stays elevated. Injection site matters too. Gluteal (buttock) injections are the standard for intramuscular delivery and provide consistent absorption. Injecting into smaller muscles or accidentally injecting into fatty tissue can alter the release rate.
Your metabolic rate, liver function, and even how physically active you are can shift the timeline slightly. Someone who exercises intensely may metabolize testosterone faster. Age also plays a role, as older adults generally clear medications more slowly. None of these factors change the half-life dramatically, but they can be the difference between feeling fine on day 12 and feeling like you’re running on empty by day 10.
The Peak-and-Trough Effect
Understanding the rise-and-fall cycle helps explain symptoms that many men on testosterone replacement notice. In the first two to three days after injection, testosterone levels are at their highest. This is when some people feel an uptick in energy, mood, and libido. By the end of the first week, levels have dropped noticeably but are usually still in a good range. During the second week on a biweekly schedule, the decline becomes more noticeable.
Common trough symptoms include fatigue, irritability, reduced motivation, and lower sex drive. These symptoms are one of the main reasons clinicians and patients shift from every-two-week dosing to weekly or twice-weekly injections. If you consistently feel worse in the days leading up to your next shot, that pattern is worth discussing with your prescriber, because adjusting the schedule often resolves it without changing the total monthly dose.
How Long Until It Fully Leaves Your System
It takes roughly five to six half-lives for a drug to be considered effectively cleared. With an eight-day half-life, that puts full clearance at about 40 to 48 days after a single injection. If you’ve been on testosterone cypionate for months or years, clearance takes longer because the drug accumulates in tissue over time. The 70-day washout period used in FDA studies reflects this: it accounts for people who have had repeated doses and need extra time for levels to return to their natural baseline.
After stopping testosterone cypionate, your body’s own testosterone production doesn’t bounce back immediately. The hypothalamic-pituitary-gonadal axis, the hormonal feedback loop that controls natural testosterone production, has been suppressed during treatment. Recovery time varies widely, from a few weeks to several months, depending on how long you were on therapy and your individual physiology.