Visualize how a drug accumulates in your system with repeated doses and clears after stopping. The chart shows concentration rising to steady-state during dosing, then exponential decay after the stop day.
Half-life is the time it takes for the concentration of a drug in your body to reduce by half. This is a key concept in pharmacokinetics—the study of how drugs move through your body over time.
When you take a medication regularly, each new dose adds to what remains from previous doses. If you take a drug with a 24-hour half-life once daily, by the time your next dose arrives, about 50% of the previous dose remains. This creates a "stacking" effect where concentration gradually rises until it reaches a steady state—the point where the amount entering your system equals the amount being eliminated.
It typically takes about 4-5 half-lives to reach steady state. For a drug with a 24-hour half-life taken daily, this means roughly 4-5 days. The chart above shows this accumulation pattern, with the sawtooth pattern representing the rise after each dose and decay between doses.
When you stop taking a medication, the concentration follows an exponential decay curve. After each half-life period, the remaining concentration halves:
Understanding half-life helps explain why some medications need to be taken multiple times daily (short half-life) while others only once (long half-life). It also explains why it can take several days to feel the full effects of a new medication, and why effects may linger after you stop taking it.