Half-life discontinuation window
Pick a medication and the date of the last dose. The tool shows the pharmacokinetic clearance window at 5 half-lives (roughly 97 percent gone), the effective half-life when an active metabolite matters, and where the drug sits on the discontinuation-symptom risk spectrum. It's a look-up for expectation setting. It doesn't replace clinical judgment on when to reintroduce or when to bridge.
Clearance window
Choose a drug and a last-dose date to see the clearance window.
Reference data current as of June 8, 2026. Sources: FDA prescribing information via DailyMed; clinician half-life quick reference guide.
How to read this
Five half-lives is the standard pharmacokinetic marker for effective clearance. It's a rule of thumb, not a hard cutoff. Some drugs matter longer than five half-lives suggest (fluoxetine's norfluoxetine metabolite), and some drugs cause discontinuation symptoms disproportionate to their pharmacokinetics (paroxetine, venlafaxine). Use the window as one input into a taper or a switch, not as the whole decision.
MAOI washout is 14 days for most serotonergic drugs and 5 weeks for fluoxetine. That interval is longer than 5 half-lives for pharmacodynamic safety, not pharmacokinetic clearance.
About this tool
Half-life is one of the most-used pharmacokinetic values in psychiatric prescribing. It determines how long a drug persists in the body after stopping, how long it takes to reach steady state after starting or dose changes, how much variation there is between doses, and how discontinuation symptoms present. This tool takes a user-entered medication and a last-dose date and returns the expected clearance window based on the FDA-labeled half-life.
The output covers three things: the 5-half-life clearance window (when roughly 97 percent of the drug has cleared, measured from the last dose date), the effective half-life when an active metabolite matters (for example, fluoxetine and norfluoxetine, or venlafaxine and desvenlafaxine), and the discontinuation-syndrome risk category based on published data and clinical experience. Discontinuation risk correlates with half-life but is not identical to it: paroxetine has similar pharmacokinetics to sertraline, but paroxetine causes much worse discontinuation symptoms because of its short half-life plus its potent SERT effects.
The calculator covers antidepressants (all SSRIs including sertraline, escitalopram, fluoxetine, paroxetine, citalopram, fluvoxamine; SNRIs; atypicals; tricyclics; MAOIs), antipsychotics (typicals and atypicals), mood stabilizers (lithium, valproate, lamotrigine, carbamazepine, oxcarbazepine), benzodiazepines, stimulants and non-stimulant ADHD agents, and other psychiatric drugs.
Two clinical uses come up most: planning a taper where knowing the pharmacokinetic clearance helps set the cadence (drugs with very short half-lives usually need slower dose reductions or conversion to longer-acting agents first), and planning an MAOI switch where the washout requirement is longer than pure clearance because the concern is serotonin syndrome or hypertensive crisis rather than drug accumulation. For the full clinical write-up, see the half-life clinician reference guide.
Common questions
- What does a 5-half-life clearance window mean?
Five half-lives is the standard pharmacokinetic benchmark for effective drug clearance. After five half-lives, about 97 percent of the drug has been eliminated from the body. It is not a hard cutoff (a small amount remains beyond that) but it is the standard reference used for washout timing between medications, MAOI switching, and estimating when steady state is reached during titration.
- Why is fluoxetine treated differently from other SSRIs for discontinuation?
Fluoxetine has a parent half-life of about 4 to 6 days and its active metabolite norfluoxetine has a half-life of 4 to 16 days. This means fluoxetine effectively self-tapers after stopping and rarely causes discontinuation symptoms. It also means the MAOI washout after fluoxetine is 5 weeks, not the standard 14 days for other SSRIs. The tool shows the effective half-life including metabolites to make this visible.
- Which antidepressants have the highest discontinuation-syndrome risk?
Paroxetine and venlafaxine consistently show the highest discontinuation-syndrome risk. Both have short half-lives (paroxetine roughly 24 hours, venlafaxine 5 hours with an active metabolite around 11 hours) and both cause substantial serotonergic rebound when stopped. Duloxetine and short-acting SNRIs are next. Fluoxetine and vortioxetine (half-life around 66 hours) sit at the low end. The tool flags each drug with a risk badge based on this.
- Does half-life predict how long side effects last after stopping?
Partially. The physical drug clears predictably by 5 half-lives. But receptor changes and downstream signaling adaptations can take longer. Post-SSRI sexual dysfunction (PSSD) and post-finasteride syndrome are examples where symptoms persist beyond the pharmacokinetic clearance window, though these are uncommon and the mechanism is not fully understood. For most patients, most side effects resolve within 1 to 2 weeks of stopping the drug.
- Is this tool useful for planning an MAOI switch?
Yes as an orientation. The standard MAOI washout is 14 days for most serotonergic antidepressants and 5 weeks for fluoxetine. These intervals are for pharmacodynamic safety (avoiding serotonin syndrome or hypertensive crisis), not pure pharmacokinetic clearance. The half-life calculation tells you when the drug has physically cleared. The washout tells you when it is safe to combine with an MAOI. See the antidepressant switching planner for the full protocol.
- Where do the half-life numbers come from?
FDA prescribing information via DailyMed is the primary source for each drug. Where the label reports a range (which is common), the tool shows the range. Active metabolite half-lives are pulled from the same source when the metabolite is clinically relevant to duration of action. Sources are cited on every result.