Sertraline vs fluoxetine.
Both block serotonin reuptake and both take weeks to work, so the clinical choice between them is made almost entirely on pharmacokinetics. That makes this pair a good test of whether you can reason from half-life and enzyme inhibition rather than from efficacy claims.
Fluoxetine has an unusually long half-life with an active metabolite lasting days, so it rarely causes discontinuation symptoms but needs a long washout before an MAOI. Sertraline is shorter acting with fewer enzyme interactions, which makes it easier to combine with other drugs.
Sertraline vs Fluoxetine at a glance
| Property | Sertraline | Fluoxetine |
|---|---|---|
| Mechanism | Serotonin reuptake inhibition | Serotonin reuptake inhibition |
| Half-life | About 26 hours | Days, with an active metabolite lasting longer |
| Discontinuation symptoms | Possible | Uncommon, because it self-tapers |
| CYP inhibition | Relatively weak | Potent CYP2D6 inhibitor |
| MAOI washout | About two weeks | Around five weeks |
| Use in pregnancy | Often preferred | Used, with more accumulated caution |
Why a long half-life cuts both ways
Fluoxetine and its active metabolite persist for days, which means missing a dose matters little and stopping the drug produces a gradual self-taper rather than the dizziness and electric-shock sensations that follow abrupt withdrawal of a shorter-acting agent. The same persistence means a serotonergic effect lingers for weeks after the last tablet, which is why the washout before starting an MAOI is so much longer.
Why CYP2D6 inhibition matters here
Fluoxetine is a potent CYP2D6 inhibitor, which affects a long list of other drugs including metoprolol, some antipsychotics and, importantly, codeine and tramadol. Blocking CYP2D6 prevents codeine being converted to morphine, so the patient gets no analgesia. Sertraline inhibits CYP2D6 far less, which is a substantial advantage in patients on several medicines.
What does not differ
Both raise synaptic serotonin, so both carry serotonin syndrome risk when combined with an MAOI, tramadol or triptans, both can cause hyponatraemia particularly in older adults, and both increase bleeding risk by depleting platelet serotonin. Both also produce side effects in the first fortnight while the benefit takes weeks, which is the counselling point that matters most.
Which one would the question pick?
Exams rarely ask what a drug does. They describe a patient and ask which of the two you would choose, so the scenarios below matter more than either drug monograph.
| Scenario | Pick | Why |
|---|---|---|
| Patient taking several other medicines | Sertraline | Weaker CYP inhibition means fewer interactions. |
| Poor adherence or frequent missed doses | Fluoxetine | Long half-life makes a missed dose largely irrelevant. |
| Patient needing codeine or tramadol | Sertraline | Fluoxetine blocks the CYP2D6 activation those drugs depend on. |
| History of severe discontinuation symptoms | Fluoxetine | Effectively self-tapering on stopping. |
Traps that catch people on this pair
Switching straight from fluoxetine to an MAOI
The active metabolite persists for weeks, so a much longer washout is required than for other SSRIs.
Missing the codeine interaction
Fluoxetine blocks CYP2D6, so codeine is not converted to morphine and provides no pain relief.
Common questions
What is the difference between sertraline and fluoxetine?
Fluoxetine has an unusually long half-life with an active metabolite lasting days, so it rarely causes discontinuation symptoms but needs a long washout before an MAOI. Sertraline is shorter acting with fewer enzyme interactions, which makes it easier to combine with other drugs.
What is the difference between sertraline and fluoxetine?
Both inhibit serotonin reuptake. Fluoxetine has a much longer half-life with an active metabolite and potently inhibits CYP2D6; sertraline is shorter acting with weaker enzyme inhibition and fewer interactions.
Why does fluoxetine need a longer washout before an MAOI?
Its active metabolite persists for weeks after the last dose, so serotonergic activity continues long after the drug is stopped, and combining it with an MAOI too soon risks serotonin syndrome.
Which SSRI has fewest drug interactions?
Sertraline is generally regarded as having a relatively favourable interaction profile among the SSRIs, whereas fluoxetine, paroxetine and fluvoxamine are stronger enzyme inhibitors.
Go deeper on the mechanism
A comparison only sticks once the shared mechanism underneath it does, because what separates two drugs is always a variation on something they have in common.
- SSRIs — the class both drugs belong to
- CNS pharmacology questions — test the distinction under time
- Serotonin syndrome versus NMS
Other comparisons
Heparin vs Warfarin · Warfarin vs DOACs · Unfractionated heparin vs Enoxaparin · Propranolol vs Atenolol · Metoprolol vs Atenolol · Amlodipine vs Nifedipine · Furosemide vs Bendroflumethiazide · Spironolactone vs Eplerenone · All comparisons
Study aid only. This page is written for learning and examination practice. It is not medical advice, not clinical decision support, and must never be used to make a decision about a real patient. Always verify against your local formulary, the product literature and a qualified pharmacist. See our medical disclaimer.
Two drugs, one property apart.
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