Concepts
Drug half-life explained
Half-life is the time it takes for a measured concentration to fall by 50% under a given model. It is a useful simplification, not a guarantee about effects or safety.
Mathematical definition
In a first-order model, concentration over time can be written as C(t) = C₀ × (½)^(t / t½), where t½ is the half-life. After 1 half-life ~50% remains, after 2 half-lives ~25%, after 4 half-lives ~6.25%, and so on.
Why multiple half-lives matter
A common rule of thumb is that 4–5 half-lives is the point where most of a single dose has been eliminated in a simple first-order model. Real pharmacokinetics can differ due to distribution into tissues, metabolites, non-linear elimination, and individual variability.
What HalfLifeDB is modeling
HalfLifeDB uses a one-compartment first-order model to visualize exponential decay. It is designed to help you understand the shape of the curve, not to provide personal medical guidance.
See the disclaimer for limitations and safety notes.