What is the most common side effect of Effexor (venlafaxine)?

Most Common Side Effects of Venlafaxine (Effexor)

Nausea is the most common side effect of venlafaxine (Effexor), occurring in approximately 37% of patients taking the medication compared to 11% in placebo groups. 1

Primary Side Effect Profile

Venlafaxine's side effect profile is characterized by several common adverse events:

• Gastrointestinal effects:

  • Nausea (37%) - most common overall side effect 1
  • Vomiting (6%) 1
  • Constipation (15%) 1
  • Anorexia (11%) 1

• Neurological effects:

  • Somnolence/drowsiness (23%) 1
  • Dizziness (19%) 1
  • Dry mouth (22%) 1
  • Insomnia (18%) 1
  • Nervousness (13%) 1

• Sexual dysfunction:

  • Abnormal ejaculation/orgasm in men (12%) 1
  • Impotence (6%) 1
  • Decreased libido (2%) 1

Discontinuation Rates Due to Side Effects

Nausea and vomiting are the most common reasons for discontinuation of venlafaxine in clinical trials 2. The FDA label reports that approximately 19% of patients discontinue treatment due to adverse events 1. The most common side effects leading to discontinuation include:

• Nausea (6% vs 1% for placebo) 1
• Somnolence (3% vs 1% for placebo) 1
• Insomnia (3% vs 1% for placebo) 1
• Dizziness (3% vs <1% for placebo) 1

Dose-Dependent Side Effects

Several side effects of venlafaxine show dose-dependency:

• Cardiovascular effects: Blood pressure elevation is more common at higher doses, particularly above 300 mg/day 3
• Gastrointestinal effects: Nausea and vomiting have a higher incidence compared to other SSRIs, especially at high doses 3

Special Considerations

Cardiovascular Effects

Venlafaxine may be associated with an increased risk for cardiovascular events 2, including:

• Dose-dependent increases in blood pressure 3
• Potential cardiac conduction abnormalities including arrhythmias, extrasystoles, and tachycardia at high doses 3

Withdrawal Syndrome

Abrupt discontinuation of venlafaxine commonly leads to withdrawal symptoms including:

• Anxiety, irritability
• Dizziness, electric shock-like sensations
• Headache, nausea, insomnia 3, 1

Comparison to Other Antidepressants

Venlafaxine has a side effect profile similar to SSRIs but with some notable differences:

• Higher incidence of nausea and vomiting than other SSRIs 2, 3
• More likely to cause blood pressure elevation than SSRIs 3, 4
• Similar rates of sexual dysfunction to SSRIs 2

Clinical Implications

When prescribing venlafaxine, clinicians should:

1. Warn patients that nausea is the most common side effect, occurring in over one-third of patients
2. Monitor blood pressure regularly, especially when initiating treatment or increasing dose
3. Consider gradual titration to minimize gastrointestinal side effects
4. Implement a tapering schedule when discontinuing to prevent withdrawal syndrome
5. Be aware that most side effects emerge within the first two weeks of treatment but often persist during continued treatment 5