Fluoxetine half-life
Fluoxetine is the antidepressant page where the metabolite story is impossible to ignore.
Effects, impairment, and testing
None of these can be calculated from half-life alone.
Therapeutic response, adverse effects, discontinuation, and norfluoxetine persistence operate on different timelines.
Half-life versus durationThe parent-drug curve cannot determine alertness, coordination, treatment response, or medication-change safety.
Safety boundaryParent fluoxetine and norfluoxetine persist on different schedules, preventing one defensible testing estimate.
Why testing is differentEvery curve begins at 100%. No dose or measured body concentration is assumed.
X-axis: elapsed time. Y-axis: modeled percentage of the relative starting point remaining. The shaded band shows the reported half-life range. This is a mathematical visualization, not a personal concentration estimate.
What a careful reader should notice first
A single curve can make persistence visible, but norfluoxetine and long washout considerations are the reason source context matters.
Source angle
Read labels and reviews for parent-versus-metabolite language before comparing fluoxetine with shorter SSRI entries.
Do not use it for
Do not use this page for switching, washout, tapering, interaction, or treatment-response decisions.
Best next step
Compare with sertraline and escitalopram, then read terminal-versus-effective half-life.
Fluoxetine: evidence and interpretation notes
One curve, two important compounds
This page uses 96 hours, or four days, for the parent drug. That value is useful for showing fluoxetine’s slow decline, but fluoxetine cannot be read well without its active metabolite, norfluoxetine. The linked labeling describes longer elimination after chronic administration and a still longer range for norfluoxetine, which is why the chart should not be mistaken for the complete pharmacokinetic story.
On the normalized parent-drug model, 50% remains after four days, 25% after eight days, and about 3% after twenty days. Those are mathematical checkpoints from one selected input. They do not predict an individual’s concentration, therapeutic response, adverse effects, or discontinuation experience.
Why repeated use changes the reading
Fluoxetine and norfluoxetine accumulate with repeated administration, and their long elimination means that steady state and washout are measured on a different scale from many shorter-acting medicines. The cited clinical pharmacokinetics review is the best starting point for that broader context. DailyMed adds product labeling; PubChem identifies the compound but does not establish the selected half-life.
| Evidence source | What it contributes | Important limit |
|---|---|---|
| DailyMed labeling | Chronic-administration and metabolite context | Label values summarize product evidence rather than an individual response |
| Clinical pharmacokinetics review | Parent range of 1 to 4 days, norfluoxetine range of 7 to 15 days, and nonlinear behavior | The review predates newer analytical and population-modeling work |
| PubChem identity record | Compound identity | It is not numerical support |
Nonlinear pharmacokinetics are another reason the smooth first-order line is an approximation. The selected four-day parent value sits at the upper end of the review’s reported parent range and reflects the chronic-administration context named beside the chart.
Keep the parent and metabolite stories separate
The chart makes the long parent-drug tail visible. It does not tell someone when to start, stop, taper, or switch fluoxetine, and it intentionally leaves treatment decisions to a prescriber or pharmacist who can account for dose history, interactions, and the active metabolite.
InterpretationReading the curve and its category context
Reading this curve
HalfLifeDB uses 4.0 days as a representative input for Fluoxetine after chronic administration. In the simplified model, about 84.1% remains after 24 hours and about 3% remains after five half-lives, or roughly 20 days.
This is a long-tail curve. The page is most useful for understanding persistence and accumulation concepts, not for making decisions from one percentage. The curve is relative: it does not estimate a person's measured concentration, effects, impairment, or time to clearance.
antidepressant context
Antidepressant half-life values often need source context because parent compounds, active metabolites, enzyme interactions, and steady-state timing can all matter.
- Half-life is not a treatment-response timeline.
- Active metabolites can make parent-compound curves incomplete.
- Stopping, tapering, switching, or combining medications requires qualified medical guidance.
ComparisonTimeline checkpoints and nearby profiles
Fluoxetine timeline checkpoints
| Elapsed time | Modeled remaining | Reading note |
|---|---|---|
| 3.0 days | 59.5% | Meaningful modeled decline, not near-zero |
| 7.0 days | 29.7% | Long-tail portion of the model |
| 14 days | 8.84% | Low modeled remainder, not a clearance guarantee |
| 30 days | 0.55% | Low modeled remainder, not a clearance guarantee |
| 60 days | 0.00% | Low modeled remainder, not a clearance guarantee |
Nearby profiles by half-life
These entries sit near Fluoxetine within the antidepressant group when sorted by representative half-life. That makes them curve comparisons, not statements about equal potency, effects, or risk.
- Escitalopram (30 h)
- Sertraline (26 h)
- Bupropion (21 h)
- Trazodone (7 h)
EvidencePharmacokinetic inputs and source trail
Pharmacokinetics at a glance
| Representative half-life | 4.0 days |
|---|---|
| Modeled analyte or phase | Fluoxetine after chronic administration |
| Reported range | 4.0 days to 6.0 days |
| Curve type | Normalized, first-order decline |
Selection note: The parent drug and norfluoxetine metabolite both matter; the chart uses a parent-drug representative value.
Sources and evidence context
A linked record is not automatically proof of the displayed value. Study, labeling, review, and compound identity sources serve different purposes; notes below identify limitations when they are known.
- Official labeling DailyMed label: FLUOXETINE HCL CAPSULE [DIRECT_RX].Official labeling used for chronic-administration and active-metabolite context.
- Identity record PubChem Compound Summary: Fluoxetine.Compound identity record; background only.
- Research abstract PubMed: Clinical pharmacokinetics of fluoxetine.Clinical review describing a 1-to-4-day parent range, 7-to-15-day norfluoxetine range, nonlinear kinetics, and hepatic context.
BoundariesWhat this page cannot answer and where to continue
What this page does not answer
- It does not estimate impairment, intoxication, or fitness to drive.
- It does not predict urine, blood, saliva, or hair test results.
- It does not model repeated exposure, tolerance, withdrawal, or interactions.
- It does not replace clinician, pharmacist, toxicologist, or emergency guidance.
Continue with context
- All substance profiles
- Browse the antidepressant group
- Compare this curve
- Clearance and volume of distribution
- Bioavailability, route, and formulation
- Active metabolites and parent compounds
- First-order vs nonlinear kinetics
- Detection windows vs half-life
- Reading labels and source quality
Read the medical disclaimer, methodology, and research standards before using the model for comparison.