What Is Half-Life?
Category: Pharmacology
The time it takes for half of a substance to be eliminated from the body. Determines dosing frequency - shorter half-life peptides need more frequent dosing.
Detailed Explanation
Half-life is a pharmacokinetic term describing the time required for the concentration of a substance in the body to decrease by 50%. After one half-life, 50% remains; after two half-lives, 25% remains; after five half-lives, less than 3% remains. For peptides, half-life is a critical determinant of dosing frequency. Peptides with short half-lives (minutes to hours) require multiple daily doses, while those with longer half-lives can be dosed weekly.
Practical Context
Understanding half-life helps optimize dosing schedules. For example, CJC-1295 without DAC has a 30-minute half-life, requiring 2-3 daily doses, while semaglutide has a 7-day half-life, allowing once-weekly dosing. BPC-157 has a 4-6 hour half-life, which is why twice-daily dosing is often recommended. When stacking peptides, aligning dosing schedules based on half-lives makes protocols more practical.
Frequently Asked Questions
How does half-life relate to how often I dose?
Generally, peptides are dosed at intervals close to their half-life to maintain therapeutic levels. Short half-life peptides (minutes to hours) need multiple daily doses, while long half-life peptides (days) can be dosed weekly.
Does a longer half-life mean a better peptide?
Not necessarily. Longer half-life provides convenience but may create continuous rather than pulsatile levels, which is less desirable for GH peptides. The 'best' half-life depends on the peptide's intended mechanism.
Related Peptides
- Semaglutide - A GLP-1 receptor agonist used for weight management and blood sugar control. (Dosage | Calculator)
- CJC-1295 (with DAC) - A GHRH analog with Drug Affinity Complex for extended half-life. (Dosage | Calculator)
- CJC-1295 (no DAC) - A GHRH analog that stimulates growth hormone release without the Drug Affinity Complex. (Dosage | Calculator)
- BPC-157 - A pentadecapeptide derived from human gastric juice, known for tissue healing properties. (Dosage | Calculator)
Related Terms
- Bioavailability - The proportion of a substance that enters the bloodstream and is available to produce an active effect. Subcutaneous injection provides near-complete bioavailability for most peptides.
- Dose-Response Curve - The relationship between the amount of peptide administered and the magnitude of its effect. Higher doses don't always mean better results and can sometimes cause diminishing returns.
- DAC (Drug Affinity Complex) - A chemical modification added to CJC-1295 that extends its half-life from minutes to about 8 days by binding to serum albumin in the blood.