Antidepressant Dose Equivalence Calculator
Research-based equivalent doses across Prozac, Zoloft, Lexapro, Paxil, and Effexor — and an honest account of what these numbers can and cannot tell you.
Approximate equivalent daily doses
| Fluoxetine (Prozac) | ≈ 41 mg |
| Escitalopram (Lexapro) | ≈ 18.5 mg |
| Paroxetine (Paxil) | ≈ 34 mg |
| Sertraline (Zoloft) | 100 mg — your dose |
| Venlafaxine (Effexor XR) | ≈ 152.5 mg |
| Citalopram (Celexa)published estimates vary | ≈ 40–67.5 mg |
These are efficacy equivalents, not taper doses. They come from comparing average doses in depression trials — they do not tell you how to reduce. Withdrawal follows receptor occupancy, which falls steeply at low doses, so taper steps must be planned as proportional reductions of your own drug with the taper schedule builder, and any switch belongs in your prescriber's hands.
Where these numbers come from: the largest published analysis of antidepressant dose equivalence — Hayasaka et al., 2015 — pooled 83 randomized double-blind trials (14,131 participants) and compared the average doses at which each drug matched fluoxetine. We show its values in fluoxetine-20mg units, the same convention used by the follow-up dose-response work in Furukawa et al., Lancet Psychiatry 2019. They are averages with real uncertainty — treat every number on this page as an approximation with a “≈” in front of it.
The equivalence chart
| Drug | Brand | ≈ Equivalent to fluoxetine 20mg/day |
|---|---|---|
| Fluoxetine | Prozac | 20 mg |
| Escitalopram | Lexapro | 9 mg |
| Paroxetine | Paxil | 17 mg |
| Sertraline | Zoloft | 49.3 mg |
| Venlafaxine | Effexor XR | 74.7 mg |
| Citalopram | Celexa | 20–33.3 mg (not in Hayasaka; published estimates span this range) |
The drugs we deliberately don't convert
An honest equivalence tool has to say “we don't know” where the research doesn't support a number.
- Duloxetine (Cymbalta): No RCT-derived fluoxetine equivalence has been published (absent from both Hayasaka 2015 and Furukawa 2019). Extrapolating from WHO defined daily doses would put fluoxetine 40 mg at duloxetine 120 mg — the licensed maximum — which shows why that shortcut is unsafe.
- Desvenlafaxine (Pristiq): The active metabolite of venlafaxine, but no validated mg-for-mg conversion between the two has been published.
Three more drugs have published efficacy comparisons but work through different receptor systems, so their “equivalents” are context, not conversions — deprescribing guidance treats them as not interchangeable with serotonin-reuptake antidepressants:
- Mirtazapine (Remeron) — noradrenergic and specific serotonergic antidepressant — does not work through serotonin reuptake. (For context, trials matched it to fluoxetine 20mg at ≈25.5mg on average.)
- Bupropion (Wellbutrin) — norepinephrine-dopamine reuptake inhibitor — no meaningful serotonin reuptake inhibition. (For context, trials matched it to fluoxetine 20mg at ≈174.3mg on average.)
- Trazodone (Desyrel) — serotonin antagonist and reuptake inhibitor with strong histamine effects; mostly prescribed for sleep at doses far below these. (For context, trials matched it to fluoxetine 20mg at ≈200.7mg on average.)
Why equivalence is not a taper plan
These values answer “what average dose treated depression about as well in trials?” — an efficacy question. Withdrawal is a different biology: serotonin transporter occupancy rises steeply at low doses and is still substantial at doses far below the therapeutic minimum, which is why Horowitz & Taylor (Lancet Psychiatry, 2019) recommend hyperbolic tapering — proportionally smaller cuts all the way down to doses far below the smallest tablet. Converting your dose to another drug's milligrams and then cutting in even steps imports the worst of both worlds. If a taper is what you're here for, the taper schedule builder plans proportional reductions of the drug you actually take.
How switching between antidepressants actually works
Clinical switching guidance (NHS Specialist Pharmacy Service; Keks et al., Australian Prescriber 2016) uses a handful of named strategies, graded by interaction risk:
- Direct switch — stop one, start the other the next day. Often possible between pharmacologically similar drugs (SSRI to SSRI or SSRI to SNRI) at comparable equivalent doses; this is where the chart above is genuinely useful to prescribers.
- Cross-taper — reduce the first while introducing the second at a low dose, typically over 2–4 weeks, paced by tolerability.
- Taper, washout, switch — the conservative route when interactions are dangerous; the washout is about five half-lives of the first drug.
- Fluoxetine is the standing exception — it lingers for 5–6 weeks after stopping, so switches off fluoxetine need a gap (days for most drugs, weeks before clomipramine or an MAOI).
- Fluoxetine bridging — switching a hard-to-stop, short-half-life drug onto fluoxetine to use its long half-life as a built-in taper. A 2025 peer-reviewed protocol stabilizes on low-dose fluoxetine for at least four weeks, then steps down with weekly dosing. Suitable for serotonin-reuptake drugs only.
Every one of these is a prescriber decision. Bring the chart to the appointment, along with the doctor conversation kit if you expect the conversation to need it.
The fine print that matters
- Values come from acute-phase depression trials in adults — nothing here is validated for anxiety disorders, OCD, pain, maintenance treatment, adolescents, or the elderly.
- Some drugs' values rest on few trials; the study's own authors caution that numbers are not uniformly robust. That's why our converter rounds.
- Higher equivalent doses are not proportionally more effective — dose-response analysis shows benefit plateauing in the fluoxetine 20–40mg range while side-effect dropouts keep climbing.
- This page is education, not medical advice. Never change drug or dose without your prescriber.
Frequently asked questions
What dose of Zoloft is equivalent to 20mg of Prozac?
About 50mg per day. In the largest published analysis of randomized trials (Hayasaka 2015), sertraline 98.5mg matched fluoxetine 40mg, which works out to roughly 49mg of sertraline (Zoloft) per 20mg of fluoxetine (Prozac). Treat it as an approximation: the values are averages across trials, not precise exchange rates.
What is the Lexapro equivalent of Zoloft?
Escitalopram (Lexapro) is the most potent common SSRI per milligram: about 9mg matches 20mg of fluoxetine, which in turn matches about 49mg of sertraline (Zoloft). So sertraline 50mg is roughly escitalopram 9-10mg, and sertraline 100mg roughly escitalopram 18-20mg — approximations from trial averages, not a prescription.
Can I use dose equivalents to plan my taper?
No — this is the single most important caveat. Equivalence values come from comparing average doses in depression efficacy trials. Withdrawal is governed by serotonin transporter occupancy, which stays high even at small fractions of a therapeutic dose. A taper has to be planned as gradual proportional reductions of the drug you are actually taking, not by converting to another drug's milligrams and cutting linearly.
Why isn't Cymbalta (duloxetine) in the converter?
Because no reliable published equivalence exists. Duloxetine is absent from both major dose-equivalence studies (Hayasaka 2015 and Furukawa 2019). Estimating it from administrative defined daily doses would equate fluoxetine 40mg with duloxetine 120mg — the licensed maximum — which is exactly the kind of implausible result that shows why we don't fill the gap with guesses.
What is cross-tapering?
Reducing the first antidepressant gradually while starting the second at a low dose and increasing it, usually over 2 to 4 weeks, at a pace set by tolerability. It is one of several switching strategies clinicians use; the alternatives are a direct next-day switch (often possible between similar SSRIs) or tapering with a washout gap when the interaction risk is high. The choice depends on both drugs' pharmacology and belongs with your prescriber.
What is fluoxetine bridging?
Switching from a short-half-life antidepressant onto fluoxetine specifically to make discontinuation smoother, because fluoxetine and its active metabolite wash out over weeks rather than hours and act as a built-in taper. A 2025 peer-reviewed protocol describes stabilizing on low-dose fluoxetine for at least four weeks and then stepping down with weekly dosing. It suits serotonin-reuptake drugs; it is not recommended for switching off bupropion, mirtazapine, or trazodone, which work through different mechanisms.
Are Wellbutrin, Remeron, or trazodone equivalent to any SSRI dose?
Not in a way you can act on. Trials have compared their effectiveness against SSRIs at average doses, but they work through different receptor systems — bupropion on norepinephrine and dopamine, mirtazapine and trazodone with strong histamine and other serotonin-receptor effects. Deprescribing guidance treats them as not interchangeable with serotonin-reuptake drugs, which is why our converter excludes them.
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