What are the side effects of Prozac (fluoxetine)?

Prozac (Fluoxetine) Side Effects

Prozac causes sexual dysfunction in 57.7% to 62.9% of patients, along with common gastrointestinal and activating side effects including nausea, insomnia, anxiety, and weight loss. 1

Most Common Side Effects

Sexual Dysfunction

• Sexual dysfunction occurs in approximately 58-63% of patients taking fluoxetine, making it one of the most prevalent adverse effects 1
• This rate is significantly higher than bupropion (8-10%) but lower than paroxetine (70.7%) 2, 1
• Sexual side effects are vastly underreported in clinical trials, so real-world rates are likely even higher 2

Gastrointestinal Effects

• Nausea, vomiting, diarrhea, and anorexia are significantly more common with fluoxetine compared to tricyclic antidepressants 3
• Anorexia (decreased appetite) occurs in 11% of patients with major depression and 17% of patients with OCD 4
• These gastrointestinal effects often require additional management strategies and can lead to discontinuation 3

Activating Effects

• Insomnia, anxiety, nervousness, agitation, and tremor are significantly more frequent with fluoxetine than with tricyclic antidepressants 3
• Anxiety and nervousness occur in 12-16% of patients with major depression 4
• Insomnia is reported in 28% of OCD patients and 33% of bulimia patients taking fluoxetine 4
• These activating effects peak early in treatment and typically decline over time 5

Weight and Appetite Changes

• Significant weight loss may occur, particularly in underweight depressed or bulimic patients 4
• Weight loss was reported in 1.4% of patients versus 0.5% on placebo 4
• This can be an undesirable result requiring monitoring throughout therapy 4

Serious but Less Common Side Effects

Seizures

• Convulsions occur in approximately 0.2% of patients, similar to other antidepressants for major depression 4
• Fluoxetine should be introduced with care in patients with a history of seizures 4

Hyponatremia

• Hyponatremia may result from syndrome of inappropriate antidiuretic hormone secretion (SIADH), with cases as low as serum sodium <110 mmol/L reported 4
• Elderly patients and those taking diuretics or who are volume depleted are at greater risk 4
• Signs include headache, difficulty concentrating, memory impairment, confusion, weakness, and unsteadiness that may lead to falls 4
• Severe cases can involve hallucination, syncope, seizure, coma, respiratory arrest, and death 4

Bleeding Risk

• SSRIs including fluoxetine increase the risk of bleeding events, ranging from ecchymoses and epistaxis to life-threatening hemorrhages 4
• Concomitant use with NSAIDs, aspirin, warfarin, or other anticoagulants significantly increases this risk 4

Mania/Hypomania Activation

• Mania or hypomania occurs in 0.7% of patients across all clinical trials 4
• This risk is similar to other antidepressants but requires monitoring, especially early in treatment 4

Cardiovascular Effects

• Mean heart rate decreases by approximately 3 beats per minute 4
• No conduction abnormalities resulting in heart block were observed in retrospective ECG evaluations of 312 patients 4
• Dysrhythmias (atrial fibrillation, bradycardia) and syncope have been reported but are uncommon 6

Oral Side Effects

• Dry mouth is the most prevalent oral adverse effect, occurring in 2.71% to 52.17% of patients 7
• Dry mouth is less frequent with fluoxetine compared to tricyclic antidepressants 7
• Dysgeusia (taste disturbance) has been reported but frequency data are limited 7

Discontinuation Syndrome

• Abrupt discontinuation can cause dysphoric mood, irritability, agitation, dizziness, sensory disturbances (electric shock sensations), anxiety, confusion, headache, lethargy, emotional lability, insomnia, and hypomania 4
• Gradual dose reduction over 10-14 days is recommended to minimize withdrawal symptoms 2, 4
• Due to fluoxetine's long elimination half-life, discontinuation symptoms may be less severe than with other SSRIs 4

Special Population Considerations

Patients with Liver Disease

• Clearance of fluoxetine and norfluoxetine is decreased in cirrhosis, requiring lower or less frequent dosing 4

Patients with Diabetes

• Fluoxetine may alter glycemic control, with hypoglycemia occurring during therapy and hyperglycemia following discontinuation 4
• Insulin and oral hypoglycemic dosages may require adjustment 4

Important Clinical Caveats

• Fluoxetine has a long elimination half-life, meaning changes in dose will not be fully reflected in plasma for several weeks, affecting both dose titration and withdrawal strategies 4
• Patients should be cautioned about operating hazardous machinery until they are certain the drug does not impair their judgment, thinking, or motor skills 4
• Black box warnings exist for treatment-emergent suicidality, particularly in adolescents and young adults 8