Glossary · Pharmacology
Half-life
In short
The half-life is the time after which half of a substance in the blood has been broken down or excreted. It helps determine how long a substance acts and how often it has to be given.
After one half-life, half is still there, after two a quarter, after about five only a few percent. That is why a substance is considered largely eliminated after about five half-lives; with regular dosing, a steady level is reached after a similar period.
Many of the body’s own peptides are stable in the blood for only minutes, because enzymes break them down quickly. Part of drug development consists of extending this time, for example by binding to blood proteins. That also changes the profile of action: short pulses can turn into a continuous signal.
The half-life in the blood is not always the same as the duration of action. Some substances keep acting through changes in tissue for longer than they can be measured.
Half-life means: how quickly the body gets rid of a substance.
Where this comes up in the fact checks
- CJC-1295 with DAC – The half-life is 5.8 to 8.1 days; after a single dose, growth hormone stayed elevated for days.
- Mod GRF 1-29 – There is no peer-reviewed human study for the substance, not even a measured half-life.
Related terms: Bioavailability · Peptide · Agonist and antagonist
Information only, not medical advice. The BK-Score is a subjective assessment according to disclosed rules – not a scientific evaluation. Scoring rules