How long does it take for venlafaxine (Effexor) to work for hot flashes?

Venlafaxine (Effexor) for Hot Flashes: Onset of Action

Venlafaxine typically begins reducing hot flashes within 4 weeks of treatment, with significant effects observed as early as the first week of therapy. 1

Efficacy Timeline

Venlafaxine demonstrates a relatively rapid onset of action for hot flash reduction:

• First week: Initial improvements may begin
• By 4 weeks: Median hot flash score reductions of 37-61% depending on dosage 1, 2
• Optimal dosing: 75 mg daily appears to be the most effective dose, with a 61% reduction in hot flash scores after 4 weeks 2
• Lower doses: Even at 37.5 mg daily, a 37% reduction in hot flash scores can be observed by week 4 2

Dosing Recommendations

• Starting dose: 37.5 mg daily 1
• Optimal dose: 75 mg daily (provides maximum benefit with manageable side effects) 1
• Higher doses: 150 mg daily shows similar efficacy to 75 mg but with increased side effects 1, 2

Comparative Efficacy

• Venlafaxine is more effective than clonidine for hot flash management, with a significantly greater reduction in hot flash frequency (7.6 vs. 4.85 hot flashes per day) after 4 weeks 3
• However, depot medroxyprogesterone acetate appears more effective than venlafaxine, with 79% vs. 55% reduction in hot flash scores after 6 weeks 4

Side Effects and Considerations

Common side effects that may appear early in treatment include:

• Dry mouth
• Decreased appetite
• Nausea
• Constipation 2

Important Clinical Considerations

• Discontinuation: Venlafaxine should be tapered gradually to prevent discontinuation symptoms due to its short-acting nature 1
• Tamoxifen interactions: Venlafaxine has minimal impact on tamoxifen metabolism compared to other antidepressants like fluoxetine and paroxetine, making it a preferred option for breast cancer patients on tamoxifen 1
• Response variability: Individual response varies significantly; some women experience >50% improvement while others may have minimal benefit 1

Treatment Algorithm

1. Start with 37.5 mg daily for one week
2. Increase to 75 mg daily if tolerated and additional benefit is needed
3. Evaluate response at 4 weeks - if inadequate response, consider:
   • Continuing for additional weeks to see if response improves
   • Switching to an alternative agent like gabapentin
4. Monitor for side effects throughout treatment

If there is no meaningful response after 4 weeks of treatment at an adequate dose, venlafaxine is unlikely to be effective for that individual 1.