Can Prozac (fluoxetine) be used for weight loss?

Fluoxetine (Prozac) Is Not Recommended for Weight Loss

Fluoxetine (Prozac) is not FDA-approved for weight loss and should not be prescribed specifically for this purpose, despite its modest and temporary weight reduction effects.

Effects of Fluoxetine on Weight

Fluoxetine may cause modest, transient weight loss through several mechanisms:

• Reduces food, energy, and carbohydrate intake 1
• Increases resting energy expenditure 1
• Can cause anorexia (decreased appetite) as a side effect 2

In clinical trials:

• 11% of patients with major depressive disorder on Prozac reported decreased appetite versus 2% on placebo 2
• Weight loss was reported in 1.4% of patients on Prozac versus 0.5% on placebo 2
• In bulimia nervosa trials, patients on Prozac 60 mg lost an average of 0.45 kg compared to a 0.16 kg weight gain with placebo over 16 weeks 2

FDA-Approved Medications for Weight Management

If weight loss is the primary goal, several FDA-approved medications should be considered instead:

1. Orlistat: Blocks absorption of about 30% of ingested fat 3
2. Phentermine/topiramate ER (Qsymia): Combination medication targeting multiple pathways 3
3. Lorcaserin (Belviq): Serotonin receptor agonist that reduces food intake 3
4. Bupropion/naltrexone SR (Contrave): Activates POMC neurons in the arcuate nucleus 3
5. Liraglutide (Saxenda): GLP-1 analogue at 3.0 mg dose 3
6. Semaglutide or Tirzepatide: Preferred pharmacotherapy for people with diabetes and obesity 3

Antidepressants and Weight Effects

Different antidepressants have varying effects on weight:

• Weight loss potential: Bupropion is the only antidepressant consistently associated with weight loss 3, 4
• Weight neutral: Most SSRIs including sertraline are generally weight neutral with long-term use 3
• Weight gain potential: Paroxetine (among SSRIs), mirtazapine, tricyclic antidepressants, and MAOIs 3, 4

Clinical Decision Making

When considering medication for weight management:

1. For primary weight loss: Use FDA-approved weight loss medications, not fluoxetine

   • These should be used as adjuncts to diet, physical activity, and behavioral counseling 3
   • Consider for patients with BMI ≥27 kg/m² with obesity-associated comorbid conditions 3

2. For patients with depression AND weight concerns:

   • Bupropion would be a better choice than fluoxetine 3, 4
   • Fluoxetine or sertraline may be reasonable alternatives if bupropion is contraindicated 3

3. Monitoring and expectations:

   • Effective weight loss medication response is typically defined as ≥5% weight loss after 3 months 3
   • Weight management medications should be continued beyond reaching weight loss goals to maintain benefits 3
   • Discontinuation often results in weight regain 3

Important Cautions

• Fluoxetine has numerous side effects including anxiety, insomnia, sexual dysfunction, and bleeding risk 2
• It has significant drug interaction potential due to inhibition of CYP2D6, CYP2C, and CYP3A4 enzymes 1, 5
• The long half-life of fluoxetine and its active metabolite (1-3 days and 7 days, respectively) means changes in dose take weeks to fully manifest 2, 6
• Fluoxetine may improve glucose tolerance in patients with type 2 diabetes, but this is not a primary indication 1

Summary

While fluoxetine may cause modest weight loss, particularly in the short term, it is not an appropriate medication choice when weight loss is the primary goal. FDA-approved weight management medications have better efficacy, more robust data, and specific indications for weight management. For patients with both depression and weight concerns, bupropion would be a more appropriate first-line option.