Testosterone Injection Dosage Chart - Half-Life by Ester and TRT Dosing
An injectable testosterone product is not one compound but a family of esters, and the ester is what decides how often the needle comes out. The same testosterone molecule is attached to a different fatty acid chain in each product, and that chain controls how quickly the depot at the injection site releases hormone into the blood. This guide works as a testosterone injection dosage chart by ester, collecting the half-lives, label doses and monitoring rules taken from product labeling, published pharmacokinetic studies and clinical practice guidance. It is educational reference material for laboratory research, not medical advice.
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How Ester Half-Life Sets the Injection Interval
Attaching an ester group at the C17 position of the molecule turns a hormone that clears within minutes into an oil depot that is absorbed slowly over days or weeks. After the injection, tissue esterases remove the ester chain and release unmodified testosterone into the circulation. Because the release step runs slower than the elimination step, the half-life of the ester behaves like the half-life of the whole product, and that number maps directly onto the dosing interval.
Two practical rules follow. First, a short ester needs short intervals: a compound with a half-life under one day cannot hold a stable level across a two week gap. Second, the wider the gap between injections relative to the half-life, the larger the swing between the high point after the dose and the low point just before the next one. Clinical guidance describes exactly this problem for intramuscular esters, where peaks and valleys in serum testosterone may be associated with fluctuations in symptoms.
Testosterone Injection Dosage Chart by Ester
| Ester | Reported half-life | Label or typical interval | Peak and trough behaviour |
|---|---|---|---|
| Testosterone propionate | About 0.8 days, roughly 19 hours | Every 2 to 3 days | Widest swing: a 50 mg dose peaked near 1159 ng/dL at 14 hours and fell to about 87 to 202 ng/dL |
| Testosterone enanthate | About 4.5 days | 50 to 400 mg every 2 to 4 weeks; 50 to 100 mg weekly when given subcutaneously | A 200 mg two weekly schedule has been reported to push peak levels above 1200 ng/dL |
| Testosterone cypionate | About 8 days | 50 to 400 mg every 2 to 4 weeks | 200 mg peaked at 1108 plus or minus 440 ng/dL at 2 to 3 days and returned to pre-injection baseline by day 14 |
| Ester blend (propionate, phenylpropionate, isocaproate, decanoate) | Mixed, because the four esters differ in length | 1 mL every 3 weeks | Testosterone returns to the lower limit of the normal range in about 21 days |
| Testosterone undecanoate | About 33.9 days in castor oil | 750 mg at initiation, again at 4 weeks, then every 10 weeks | Peak at a median of 7 days; steady state trough about 324 ng/dL |
Two details in that chart matter more than the rest. The blend is not a single ester: the 250 mg/mL format contains 30 mg of propionate, 60 mg of phenylpropionate, 60 mg of isocaproate and 100 mg of decanoate, so one injection delivers a fast front loaded component plus a slow tail. Undecanoate is built the other way around, a single long chain that supports a ten week gap, which is why its half-life is measured in weeks rather than days.
Catalog listings such as Propionat 100 (testosterone propionate) sit at the short end of that range, which is why the same milligram amount behaves completely differently depending on which ester label it carries.
Testosterone Cypionate Dosage and Testosterone Enanthate Dosage
Cypionate and enanthate are the two esters most often compared, and their label intervals are identical: 50 to 400 mg given every two to four weeks. The difference sits in the release rate. Cypionate is listed with an intramuscular half-life of approximately eight days, while enanthate is reported at about 4.5 days, so enanthate clears faster and produces a shorter, sharper curve at the same milligram dose.
The measured profile of a 200 mg cypionate injection shows what a two week schedule really looks like. Serum testosterone peaked at 1108 plus or minus 440 ng/dL between day 2 and day 3, began to fall from day 5, and was back at the pre-injection level by day 14. In practice that means the first half of the cycle sits above the physiological mid-range and the second half sits below it, which is the fluctuation clinical guidance warns about.
Weekly subcutaneous enanthate was designed to remove that swing. The product labeling sets a starting dose of 75 mg once weekly, with adjustment across a 50 to 100 mg weekly range, and the recorded profile after 12 weeks of weekly dosing shows a median time to peak of 11.9 hours and a pre-dose trough of 436 ng/dL. Steady state was reached by week 6. A reference product such as Cypionat 250 or Enantat 250 is the oil based intramuscular form of the same chemistry, carrying the same ester driven release behaviour.
Injection Frequency, TRT Dose and the Long Acting Options
Replacement guidance does not fix a single number. It sets a target band and tells the clinician to titrate into it: serum testosterone should sit in the mid-normal range, and for enanthate or cypionate the working check is a mid-interval level between 350 and 600 ng/dL, with a dose or frequency change if the reading falls outside that window. Subcutaneous enanthate uses the same logic with a slightly different band, a pre-dose target of at least 350 and below 650 ng/dL.
For the long acting esters the schedule is built into the molecule:
- Undecanoate, 750 mg - given at initiation, repeated at 4 weeks, then every 10 weeks. At steady state the average level was 495 ng/dL, with a peak of 891 ng/dL and a trough of 324 ng/dL. See Undecanoate 250.
- Ester blends - a 1 mL injection every 3 weeks is the labeled schedule, with testosterone falling back to the lower limit of normal in about 21 days. See Sustanon 270.
- Propionate - a half-life under one day forces a 2 to 3 day rhythm, which is why it is the least convenient option for long term replacement.
Frequency, not dose alone, shapes the curve, and testosterone injection frequency is therefore a property of the ester rather than a matter of preference. Because the peak to trough spread follows from the gap between injections, halving the dose and halving the interval narrows both the high and the low points while keeping the same total amount of hormone per week. That is the reasoning behind split weekly or twice weekly schedules, and it is also why guidance insists on measuring levels between doses rather than ignoring the timing of the last injection.
When to Draw Labs: Peak, Trough and Steady State
Timing the blood draw matters as much as the number on the report. Guidance calls for testosterone and hematocrit to be checked 3 to 6 months after starting therapy, then again at 12 months and annually, and it specifies where in the cycle to sample:
- Enanthate and cypionate - sample midway between injections. A mid-interval level above 600 ng/dL or below 350 ng/dL calls for a dose or frequency adjustment.
- Undecanoate - sample at the end of the dosing interval, just before the next injection, and aim for the nadir to land in the mid-normal range.
- Weekly subcutaneous enanthate - the label specifies a trough drawn 7 days after the most recent dose, first at week 6 and then periodically.
The concept underneath is steady state. Levels accumulate for several half-lives after a schedule starts, and a number read too early reflects the build up rather than the plateau, which is why the labeled monitoring point sits six weeks into weekly dosing. Before treatment is started at all, the diagnosis is confirmed on at least two separate morning measurements, because testosterone follows a daily rhythm and a single afternoon sample can mislead.
Signs of Excess, Signs of Insufficiency and the Main Risks
Because the esters differ only in release speed, the safety picture is driven by exposure rather than by the molecule. Guidance lists fluctuation in mood or libido alongside injection site pain as formulation specific effects, and notes that a small fraction of men on intramuscular testosterone reach supraphysiologic concentrations, which is where dose related adverse effects concentrate.
- Too high - hematocrit and hemoglobin climbing, new or worsening blood pressure, fluid retention, acne, irritability, and in some men a fall in libido rather than a rise.
- Too low - the original deficiency symptoms returning before the next dose: fatigue, low mood, poor libido, loss of morning erections, and a trough reading under 350 ng/dL.
Three risks deserve naming. Erythrocytosis is the most frequent one: testosterone therapy raises red cell mass, men receiving it were significantly more likely to reach a hematocrit above 54 percent, and most guidance treats a value above that threshold as a trigger to stop and consider phlebotomy. A starting hematocrit above 48 percent is itself considered a relative reason not to begin. Blood pressure rises too, with 24 hour monitoring in one weekly product showing an average increase of 3.9 over 1.5 mm Hg after 12 weeks of treatment. Finally, exogenous testosterone suppresses luteinizing hormone and follicle stimulating hormone, which shuts down the signal that keeps intratesticular testosterone and sperm production running, so guidance recommends against starting therapy in men who plan fertility in the near term. Protocols that need to protect testicular function instead use agents that act like LH at the testis, such as hCG 2500 IU.