Fluoxetine: Difference between revisions
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MDElliottMD (talk | contribs) Add SSRI suicidality boxed warning (monitoring + counseling) and MAOI contraindication / serotonin-syndrome interactions; reconcile half-life to FDA label. Parser pharm-audit fix, mark-greenlit, servops-applied. |
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| brand = Prozac | | brand = Prozac | ||
| structure = Fluoxwhite.svg | | structure = Fluoxwhite.svg | ||
| classes = SSRI, Anxiolytic, Antidepressant | | classes = [[:Category:Selective Serotonin Reuptake Inhibitors (SSRIs)|SSRI]], [[:Category:Anxiolytics|Anxiolytic]], [[:Category:Antidepressants|Antidepressant]] | ||
| uses = Anxiety, premature ejaculation, low mood | | uses = <vote slug="anxiety-use">Anxiety</vote>, <vote slug="premature-ejaculation-use">Premature ejaculation</vote>, <vote slug="low-mood-use">Low mood</vote> | ||
| starting_dose = 10 mg | | starting_dose = 10 mg | ||
| preparations = 10 mg, 20 mg, 40 mg caps | | preparations = 10 mg, 20 mg, 40 mg caps | ||
| fda_max = 40 mg/d | | fda_max = 40 mg/d | ||
| pill_id = | |||
* '''10 mg:''' green/cream capsule, "PLIVA 647" | |||
* '''20 mg:''' green/cream capsule, "PROZAC 20" | |||
* '''40 mg:''' olive/cream capsule, "DISTA 3107" | |||
* '''Oral solution:''' 20 mg / 5 mL, clear | |||
| routes = Oral | | routes = Oral | ||
| onset = | | onset = | ||
| duration = Very long | | duration = Very long | ||
| halflife = | | halflife = 1-3 days acute, 4-6 days chronic; 4-16 days for norfluoxetine<ref name="prozac-label"/> | ||
| bioavailability = 70–90% (oral) | | bioavailability = 70–90% (oral) | ||
| pregnancy = Category C<ref name ="lactmed"> | | pregnancy = Category C<ref name="lactmed">S0</ref> | ||
| legal = Rx-only in US | | legal = [[USLegal:Prescription only|Rx-only]] in US | ||
| mechanism = TrkB/BDNF<ref name="trkb"> | | mechanism = TrkB/BDNF<ref name="trkb">S1</ref> <vote slug="ssri-claim">Fluoxetine is a selective serotonin reuptake inhibitor.</vote> | ||
| intro = Fluoxetine was the first | | intro = Fluoxetine, marketed as Prozac, was the first selective serotonin reuptake inhibitor ([[:Category:Selective_Serotonin_Reuptake_Inhibitors_(SSRIs)|SSRIs]]) brought to market and the medicine that opened the SSRI era. It was discovered at Eli Lilly's laboratories in Indianapolis on 24 July 1972 by a team that included the chemists Bryan Molloy and Klaus Schmiegel and the pharmacologist David Wong,<ref name="wong1974">Wong DT, Horng JS, Bymaster FP, Hauser KL, Molloy BB. A selective inhibitor of serotonin uptake: Lilly 110140, 3-(p-trifluoromethylphenoxy)-N-methyl-3-phenylpropylamine. Life Sciences. 1974;15(3):471-479. PMID: 4549929.</ref> approved by the FDA in December 1987, and launched in the United States as Prozac in January 1988. It is notable for the extremely long half-life of its active metabolite norfluoxetine, which gives the medicine an unusually mild discontinuation profile and makes it useful as a bridge in tapering patients off shorter-acting serotonergic medicines. | ||
| history = The compound that became fluoxetine emerged from an Eli Lilly program that began in the late 1960s under Molloy and Schmiegel, who synthesized a series of aryloxyphenylpropylamines starting from the antihistamine [[Diphenhydramine|diphenhydramine]] as a structural lead. Wong, who had followed the European literature implicating serotonin in mood regulation, proposed screening the new compounds specifically for serotonin uptake inhibition. On 24 July 1972 the team identified the compound then designated Lilly 110140 as a potent and selective inhibitor of serotonin uptake in rat brain synaptosomes. The finding was published in 1974 as the first description of what is now known as a selective serotonin reuptake inhibitor.<ref name="wong1974"/> | |||
Lilly renamed the compound fluoxetine in 1975, filed an investigational application with the FDA, and pursued clinical development through the late 1970s and early 1980s. The FDA approved fluoxetine for major depressive disorder in December 1987, and Lilly launched it as Prozac in January 1988. The marketing name itself was a departure: medicines had historically been named to reflect chemical structure, and Prozac was among the first to be commissioned from an outside naming firm. Within five years of launch Prozac was one of the most prescribed medicines in the United States, and Peter Kramer's 1993 book Listening to Prozac made the SSRI era a subject of popular discussion. Lilly's US patent expired in August 2001, after which generic fluoxetine became broadly available. | |||
Fluoxetine is a prescription-only medicine in the United States. It remains on the WHO Model List of Essential Medicines and is one of the most widely prescribed serotonergic medicines worldwide. The serotonergic framing under which the medicine was discovered and marketed has not aged uniformly well; the TrkB/BDNF account of its mechanism, developed primarily in the 2000s, is the principal contemporary alternative and is reflected in the mechanism field above. | |||
| indications = | | indications = <problem ref="depression" author="MDElliottMD"/> | ||
<problem ref="anxiety-disorders" author="MDElliottMD"> | |||
Including generalized anxiety, panic, and social anxiety. | |||
</problem> | |||
<problem ref="panic" author="MDElliottMD"/> | |||
<problem ref="social-anxiety" author="MDElliottMD"/> | |||
<problem ref="ocd" author="MDElliottMD"/> | |||
<problem ref="ptsd" author="MDElliottMD"> | |||
Potentially. | |||
</problem> | |||
<problem ref="premature-ejaculation"/> | |||
| dosing = <titration slug="standard" author="MDElliottMD" title="Standard adult or child"> | | dosing = <titration slug="standard" author="MDElliottMD" title="Standard adult or child"> | ||
Start no higher than 10 mg for the first dose. May increase by 10 mg every 2–12 weeks, or remain at 10 mg if the response is adequate, up to a typical starting maximum of 40 mg. Absolute max: 80 mg. | Start no higher than 10 mg for the first dose. May increase by 10 mg every 2–12 weeks, or remain at 10 mg if the response is adequate, up to a typical starting maximum of 40 mg. Absolute max: 80 mg. | ||
| Line 30: | Line 47: | ||
Start at 10 mg daily; increase by 10–20 mg every 2–6 weeks, up to 80 mg. OCD typically requires elevated doses (60–80 mg). | Start at 10 mg daily; increase by 10–20 mg every 2–6 weeks, up to 80 mg. OCD typically requires elevated doses (60–80 mg). | ||
</titration> | </titration> | ||
| effects = <effect ref="anxiolysis" author="MDElliottMD">Classically starting at 3–4 weeks and improving for another 8–12.</effect> | | effects = | ||
<effect ref="delayed-ejaculation" author="MDElliottMD"/> | * <effect ref="anxiolysis" author="MDElliottMD">Classically starting at 3–4 weeks and improving for another 8–12.</effect> | ||
<effect ref="mood-enhancement" author="MDElliottMD"/> | * <effect ref="delayed-ejaculation" author="MDElliottMD"/> | ||
<effect ref="nausea" author="MDElliottMD">Common, often improves over 1–2 weeks.</effect> | * <effect ref="mood-enhancement" author="MDElliottMD"/> | ||
<effect ref="decreased-libido" author="MDElliottMD"/> | * <effect ref="nausea" author="MDElliottMD">Common, often improves over 1–2 weeks.</effect> | ||
<effect ref="temporary-erectile-dysfunction" author="MDElliottMD"/> | * <effect ref="decreased-libido" author="MDElliottMD"/> | ||
<effect ref="persistent-sexual-dysfunction" author="MDElliottMD"> | * <effect ref="temporary-erectile-dysfunction" author="MDElliottMD"/> | ||
* <effect ref="persistent-sexual-dysfunction" author="MDElliottMD">Historically [https://pmc.ncbi.nlm.nih.gov/articles/PMC11450419/ associated with SSRIs].</effect> | |||
</ | |||
| | <effect ref="anorgasmia" author="MDElliottMD"/> | ||
| interactions = | | pk_absorption = 70–90%<ref name="statpearls">S3</ref> oral bioavailability. | ||
| pk_distribution = Fluoxetine has plasma protein binding of approximately 94.5%, bound to albumin and alpha-1 glycoprotein. Fluoxetine readily crosses the blood–brain barrier, with a brain-to-plasma ratio of 2.6:1 in humans. The volume of distribution (Vd) of fluoxetine and its metabolite ranges between 20 to 42 L/kg. Some studies report that fluoxetine has the maximum volume of distribution (Vd) of any SSRI (between 14 and 100 L/kg).<ref name="statpearls"/> | |||
| pk_metabolism = Fluoxetine's active metabolite is norfluoxetine, produced when the cytochrome P450 enzyme ([[Enzyme:CYP2D6|CYP2D6]]) acts on it. Prescribers must remember that fluoxetine has several med-med interactions due to its metabolism through the CYP2D6 isoenzyme. Additionally, norfluoxetine can have an inhibitory effect on [[Enzyme:CYP3A4|CYP3A4]]. Fluoxetine has an elimination half-life of 1 to 3 days after a single dose and 4 to 6 days with chronic dosing, and its active metabolite norfluoxetine has a half-life of 4 to 16 days.<ref name="prozac-label"/> Approximately 7% of individuals definitively exhibit poor metabolism of fluoxetine due to reduced activity of CYP2D6.<ref name="statpearls"/> | |||
| pk_elimination = | |||
| pharmacodynamics = | |||
| interactions = <pharmaInteractions/> | |||
The clinically important interactions for prescribers: | |||
* '''MAO inhibitors: contraindicated.''' Combination with non-selective MAOIs (isocarboxazid, phenelzine, tranylcypromine), or with linezolid or intravenous methylene blue, can produce serotonin syndrome, which may be life-threatening. At least 14 days must elapse between stopping an MAOI and starting fluoxetine. Because of the long half-life of fluoxetine and its active metabolite norfluoxetine, at least 5 weeks must elapse between stopping fluoxetine and starting an MAOI.<ref name="prozac-label">U.S. Food and Drug Administration. Prozac (fluoxetine hydrochloride) prescribing information. NDA 018936.</ref> | |||
* '''Other serotonergic medicines: serotonin-syndrome risk.''' Triptans, tramadol, other SSRIs and SNRIs, lithium, and St John's wort raise serotonergic load; combine with caution and counsel on serotonin-syndrome symptoms. | |||
* '''Strong CYP2D6 inhibition.''' Fluoxetine is a strong CYP2D6 inhibitor and norfluoxetine inhibits CYP3A4, so levels of many CYP2D6 substrates rise (several tricyclics, some neuroleptics, metoprolol, atomoxetine; tamoxifen activation is blunted). Because of the long half-life, this effect persists for weeks after fluoxetine is stopped. | |||
| pregnancy_details = | | pregnancy_details = | ||
| monitoring = | | monitoring = '''Boxed warning: monitor closely for worsening mood, suicidal ideation, and behavioral activation,''' especially during the first weeks of treatment, with any dose change, and particularly in patients under age 25. No routine laboratory monitoring required. Because of fluoxetine's very long effective half-life, both therapeutic change and adverse effects (including activation or emergent suicidality) appear and resolve more slowly than with shorter-acting SSRIs. Watch for emergent manic or hypomanic symptoms throughout treatment and treat new rapid mood elevation, agitation, or pressured speech as a possible bipolar switch. | ||
| counseling = | | counseling = '''Before starting:''' screen for a personal or family history of bipolar disorder; fluoxetine, like all antidepressants, can precipitate a manic or mixed switch in susceptible patients. '''Boxed warning:''' counsel patients (and family members, where appropriate) about the increased risk of suicidal ideation and behavioral activation in patients under 25, and ask them to report promptly any worsening mood, intrusive thoughts of self-harm, agitation, irritability, or unusual behavioral changes, particularly in the first weeks of treatment and after any dose change. | ||
| anecdotes = <anecdote slug="2026-05-12" perspective="provider" author="MDElliottMD"> | | anecdotes = <anecdote slug="2026-05-12" perspective="provider" author="MDElliottMD"> | ||
Fluoxetine is great for getting off other SxRIs! Especially venlafaxine and duloxetine. | Fluoxetine is great for getting off other SxRIs! Especially [[Venlafaxine|venlafaxine]] and [[Duloxetine|duloxetine]]. | ||
</anecdote> | </anecdote> | ||
| seealso = [[Sertraline]], [[Duloxetine]] | | seealso = [[Sertraline]], [[Duloxetine]] | ||
| references = <references/> | | references = <references/> | ||
}} | }} | ||
[[Category:Selective Serotonin Reuptake Inhibitors (SSRIs)]] | |||
[[Category:Antidepressants]] | |||
[[Category:Medicines]] | |||
Latest revision as of 13:10, 10 June 2026
History
The compound that became fluoxetine emerged from an Eli Lilly program that began in the late 1960s under Molloy and Schmiegel, who synthesized a series of aryloxyphenylpropylamines starting from the antihistamine diphenhydramine as a structural lead. Wong, who had followed the European literature implicating serotonin in mood regulation, proposed screening the new compounds specifically for serotonin uptake inhibition. On 24 July 1972 the team identified the compound then designated Lilly 110140 as a potent and selective inhibitor of serotonin uptake in rat brain synaptosomes. The finding was published in 1974 as the first description of what is now known as a selective serotonin reuptake inhibitor.[4]
Lilly renamed the compound fluoxetine in 1975, filed an investigational application with the FDA, and pursued clinical development through the late 1970s and early 1980s. The FDA approved fluoxetine for major depressive disorder in December 1987, and Lilly launched it as Prozac in January 1988. The marketing name itself was a departure: medicines had historically been named to reflect chemical structure, and Prozac was among the first to be commissioned from an outside naming firm. Within five years of launch Prozac was one of the most prescribed medicines in the United States, and Peter Kramer's 1993 book Listening to Prozac made the SSRI era a subject of popular discussion. Lilly's US patent expired in August 2001, after which generic fluoxetine became broadly available.
Fluoxetine is a prescription-only medicine in the United States. It remains on the WHO Model List of Essential Medicines and is one of the most widely prescribed serotonergic medicines worldwide. The serotonergic framing under which the medicine was discovered and marketed has not aged uniformly well; the TrkB/BDNF account of its mechanism, developed primarily in the 2000s, is the principal contemporary alternative and is reflected in the mechanism field above.Experience
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Problems
Titration strategies
Effects
- Anxiolysis no reports yet ~33% +67.0 (n=1)Classically starting at 3–4 weeks and improving for another 8–12.Did you experience this?How often have you seen this?How was it? (-100 worst, +100 best)How was it? (-100 worst, +100 best)
- Delayed orgasm/ejaculation 0% — (n=3) ~80% +38.0 (n=1)Did you experience this?How often have you seen this?How was it? (-100 worst, +100 best)How was it? (-100 worst, +100 best)
- Mood enhancement no reports yet ~5% +67.0 (n=1)Did you experience this?How often have you seen this?How was it? (-100 worst, +100 best)How was it? (-100 worst, +100 best)
- Nausea no reports yet ~5% -33.0 (n=1)Common, often improves over 1–2 weeks.Did you experience this?How often have you seen this?How was it? (-100 worst, +100 best)How was it? (-100 worst, +100 best)
- Decreased libido no reports yet ~33% -100.0 (n=1)Did you experience this?How often have you seen this?How was it? (-100 worst, +100 best)How was it? (-100 worst, +100 best)
- Temporary erectile dysfunction no reports yet ~20% -67.0 (n=1)Did you experience this?How often have you seen this?How was it? (-100 worst, +100 best)How was it? (-100 worst, +100 best)
- Persistent Sexual Dysfunction no reports yet ~0% -100.0 (n=1)Historically associated with SSRIs.Did you experience this?How often have you seen this?How was it? (-100 worst, +100 best)How was it? (-100 worst, +100 best)
Pharmacokinetics
Absorption
70–90%[5] oral bioavailability.Distribution
Fluoxetine has plasma protein binding of approximately 94.5%, bound to albumin and alpha-1 glycoprotein. Fluoxetine readily crosses the blood–brain barrier, with a brain-to-plasma ratio of 2.6:1 in humans. The volume of distribution (Vd) of fluoxetine and its metabolite ranges between 20 to 42 L/kg. Some studies report that fluoxetine has the maximum volume of distribution (Vd) of any SSRI (between 14 and 100 L/kg).[5]Metabolism
Fluoxetine's active metabolite is norfluoxetine, produced when the cytochrome P450 enzyme (CYP2D6) acts on it. Prescribers must remember that fluoxetine has several med-med interactions due to its metabolism through the CYP2D6 isoenzyme. Additionally, norfluoxetine can have an inhibitory effect on CYP3A4. Fluoxetine has an elimination half-life of 1 to 3 days after a single dose and 4 to 6 days with chronic dosing, and its active metabolite norfluoxetine has a half-life of 4 to 16 days.[2] Approximately 7% of individuals definitively exhibit poor metabolism of fluoxetine due to reduced activity of CYP2D6.[5]Interactions
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Patient experience
- Generally a blunted MDMA effect is reported, though I have heard many reports of people having full effects despite full-dose steady state SSRI use comcotitantly
- checking this mechanism here
- generally surprisingly well!
The clinically important interactions for prescribers:
- MAO inhibitors: contraindicated. Combination with non-selective MAOIs (isocarboxazid, phenelzine, tranylcypromine), or with linezolid or intravenous methylene blue, can produce serotonin syndrome, which may be life-threatening. At least 14 days must elapse between stopping an MAOI and starting fluoxetine. Because of the long half-life of fluoxetine and its active metabolite norfluoxetine, at least 5 weeks must elapse between stopping fluoxetine and starting an MAOI.[2]
- Other serotonergic medicines: serotonin-syndrome risk. Triptans, tramadol, other SSRIs and SNRIs, lithium, and St John's wort raise serotonergic load; combine with caution and counsel on serotonin-syndrome symptoms.
- Strong CYP2D6 inhibition. Fluoxetine is a strong CYP2D6 inhibitor and norfluoxetine inhibits CYP3A4, so levels of many CYP2D6 substrates rise (several tricyclics, some neuroleptics, metoprolol, atomoxetine; tamoxifen activation is blunted). Because of the long half-life, this effect persists for weeks after fluoxetine is stopped.
Monitoring
Patient counseling
Relevant anecdote
Relevant Literature
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See also
References
- ↑ S1
- ↑ 2.0 2.1 2.2 U.S. Food and Drug Administration. Prozac (fluoxetine hydrochloride) prescribing information. NDA 018936.
- ↑ S0
- ↑ 4.0 4.1 Wong DT, Horng JS, Bymaster FP, Hauser KL, Molloy BB. A selective inhibitor of serotonin uptake: Lilly 110140, 3-(p-trifluoromethylphenoxy)-N-methyl-3-phenylpropylamine. Life Sciences. 1974;15(3):471-479. PMID: 4549929.
- ↑ 5.0 5.1 5.2 S3
- 10 mg: green/cream capsule, "PLIVA 647"
- 20 mg: green/cream capsule, "PROZAC 20"
- 40 mg: olive/cream capsule, "DISTA 3107"
- Oral solution: 20 mg / 5 mL, clear
- Depressive disorders1.0n=1
- Anxiety disorders broadly4.0n=2
- Panic disorder1.3n=2
- Social anxiety disorder1.0n=1
- Obsessive-compulsive disorder3.0n=1