Fluoxetine (Prozac): Uses, Dosage, Side Effects, and What to Expect

Fluoxetine (brand name: Prozac) is a selective serotonin reuptake inhibitor (ssri). Fluoxetine blocks serotonin reuptake and has a uniquely long half-life (2-6 days for the parent compound, 4-16 days for its active metabolite norfluoxetine). This long half-life makes it the most forgiving SSRI if doses are missed and produces the least discontinuation syndrome of any SSRI. Fluoxetine also has mild norepinephrine reuptake inhibition and 5-HT2C antagonism, which may contribute to its activating profile.

• Major Depressive Disorder (MDD)
• Obsessive-Compulsive Disorder (OCD)
• Panic Disorder
• Bulimia Nervosa
• Bipolar Depression (in combination with olanzapine, as Symbyax)

Common off-label uses:

• Generalized Anxiety Disorder
• PTSD
• Premature Ejaculation
• Body Dysmorphic Disorder
• Binge Eating Disorder

Adults typically start at 20 mg once daily in the morning. For depression, doses range from 20-80 mg/day. Bulimia nervosa usually requires 60 mg/day. OCD may need 40-80 mg/day. A weekly formulation (90 mg capsule) is available for maintenance therapy.

Initial effects may appear within 1-2 weeks. Full antidepressant response in 4-6 weeks. OCD may take 8-12 weeks.

• Nausea
• Headache
• Insomnia (more activating than other SSRIs)
• Nervousness or anxiety (early in treatment)
• Sexual dysfunction
• Decreased appetite
• Tremor

• Serotonin syndrome
• Suicidal ideation in young adults (FDA black box warning)
• Mania/hypomania activation
• Prolonged QT interval at high doses
• Abnormal bleeding

Strong CYP2D6 inhibitor — significantly increases levels of many medications including tamoxifen, codeine (reduces efficacy), and tricyclic antidepressants. Contraindicated with MAOIs. Due to its long half-life, wait 5 weeks after stopping fluoxetine before starting an MAOI.

The most-studied SSRI in pregnancy. Generally considered relatively safe, though the same class-level risks apply. Often chosen when an SSRI is needed during pregnancy due to the extensive safety data available.

Due to its very long half-life, fluoxetine essentially self-tapers. Discontinuation syndrome is rare, making it the easiest SSRI to stop.