Half-Life Calculator
Visualize how a peptide's concentration changes over time. Enter the half-life and dose to see the decay curve and optimal redose window.
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Redosed every 1 half-life
Blood Concentration Over Time
This model assumes first-order elimination kinetics and immediate absorption. Actual pharmacokinetics vary based on administration route, individual metabolism, and other factors.
Understanding Peptide Half-Life
Half-life is the most important pharmacokinetic property for determining how often to dose a peptide. It tells you how long the peptide stays active in your body and directly determines dosing frequency. A peptide with a 2-hour half-life (like Ipamorelin) needs to be dosed multiple times daily, while one with a 7-day half-life (like Semaglutide) only requires weekly injection.
After one half-life, 50% of the original dose remains in your bloodstream. After two half-lives, 25% remains. After five half-lives, less than 3.125% remains — this is the point at which a drug is considered effectively eliminated. This exponential decay follows the same mathematical pattern regardless of the dose or the specific peptide.
How Half-Life Affects Dosing
Short half-life peptides like CJC-1295 no-DAC (30 minutes) and Sermorelin (10-12 minutes) produce brief, pulsatile effects. They are dosed 2-3 times daily to maintain meaningful blood levels. This pulsatile pattern is actually desirable for growth hormone peptides because it mimics the body's natural GH secretion rhythm.
Long half-life peptides like Semaglutide (168 hours / 7 days) and MK-677 (24 hours) maintain sustained blood levels with less frequent dosing. This is convenient but also means side effects persist longer. If you have a bad reaction to a weekly Semaglutide injection, it takes weeks to fully clear your system.
When dosing at intervals equal to one half-life, the trough level (lowest point before next dose) stabilizes at approximately the same level as the dose amount after about 5 doses. This steady-state is when you experience the full therapeutic effect.
Frequently Asked Questions
What is a peptide half-life?
Half-life is the time it takes for the concentration of a peptide in your body to decrease by half. A peptide with a 2-hour half-life will be at 50% concentration after 2 hours, 25% after 4 hours, and 12.5% after 6 hours. It determines how often you need to redose to maintain effective blood levels.
How many half-lives until a peptide is eliminated?
After approximately 5 half-lives, a peptide is considered effectively eliminated from the body (less than 3.125% remaining). For Ipamorelin (2-hour half-life), that is 10 hours. For Semaglutide (7-day half-life), that is 5 weeks.
Does a longer half-life mean a peptide is more effective?
No. Half-life only determines how long the peptide stays in your system, not how potent it is. A short half-life peptide can be extremely effective — it just requires more frequent dosing. In fact, for growth hormone peptides, shorter half-lives are often preferred because they create a natural pulsatile release pattern.