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TRT: Twice weekly injections, half-lives, & reaching steady-state

TRT Injections work best when done twice a week
Testosterone Cypionate: Twice weekly Injections

When it comes to administering testosterone cypionate, a widely used form of exogenous testosterone, the frequency of injections plays a crucial role in achieving optimal therapeutic outcomes.


Testosterone levels in the body naturally fluctuate throughout the week, following a diurnal rhythm with peak levels in the morning and lower levels in the evening. Mimicking this natural pattern with a twice-weekly injection protocol helps maintain more stable testosterone levels.

By avoiding peaks and troughs associated with less frequent injections, twice-weekly administration supports a more balanced and controlled hormonal environment, enhancing the effectiveness of TRT while minimizing the risk of adverse effects.

Overall, the regimen aligns with the pharmacokinetics of testosterone cypionate.

Here are the half-lives of testosterone cypionate:

Day 0: Administration of testosterone cypionate--100%

Day 8: Approximately half of the administered dose is eliminated--50%

Day 16: Another half (half of half, if you will) of the remaining dose is eliminated, leaving around 25% of the initial dose

Day 24: Approximately (half of 25%) 12.5% of the initial dose remains

...and so forth

Don't even get me started on mean residence time (MRT). This is 1.5-2xs the half-life, which is 12 to 16 days. This is the last of the last molecule of testosterone cypionate remaining after day 0 of injecting.

Quick Fun Fact:

  • The half-life of Test Cyp is 8 days.

  • Steady-state is reached in five half-lives, so about 35-45 days --time to repeat labs

  • hCG half-life is up to 36 hours

  • Steady-state is reached in five half-lives, so about 7.5 days

  • hCG at low doses helps maintain about 93% of testicular function (without it, you lose 94% of intratesticular function) for steroidogenesis and spermatogenesis

The Goal: Achieve a steady state where administration equals elimination.

By dividing the total weekly dose into two smaller injections, patients may experience more consistent symptom relief. This approach helps prevent the sharp peak-and-trough fluctuations.

Mitigating Side Effects:

A twice-weekly injection schedule may help minimize potential side effects associated with TRT:

  • Reduces the impact on hematocrit levels and hematocrit-related complications

  • Stabilizes hormone levels

  • Stabilizes mood and mood swings

  • Better manage estradiol levels

  • A stable hormone environment supports muscle mass, bone density, libido, fatigue, and energy

  • Mimics natural testosterone release (the testes release anywhere from 4 - 7 mg up to 14 mg of natural testosterone per day)

The takeaway: Twice weekly injections of testosterone cypionate for men on TRT help reach a steady state and better control negative symptoms.

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