Potential Side Effects of Venlafaxine
Venlafaxine commonly causes gastrointestinal effects (especially nausea), neurological effects (dizziness, headache), sexual dysfunction, and can cause dose-dependent increases in blood pressure, with serious risks including discontinuation syndrome and serotonin syndrome. 1, 2
Common Side Effects
Gastrointestinal Effects
- Nausea is the most common side effect and the most frequent reason for discontinuation (6% of patients), though it typically resolves within 1-3 weeks of starting treatment 1, 2
- Other common gastrointestinal effects include vomiting (6%), constipation (15%), dry mouth (22%), decreased appetite/anorexia (11%), and diarrhea (8%) 1, 2
Neurological Effects
- Dizziness (19%), headache (3%), somnolence/drowsiness (23%), insomnia (18%), and nervousness (13%) are frequently reported 1, 2
- Tremor (5%) may occur and is dose-dependent, becoming more common at higher doses 2
Cardiovascular Effects
- Dose-dependent increases in blood pressure, with higher risk at doses above 300 mg/day 1
- Blood pressure monitoring is essential, especially when initiating treatment or adjusting dosage 1
- Incidence of hypertension increases with dose: 3-5% at doses ≤200 mg/day, 7% at 201-300 mg/day, and 13% at >300 mg/day (vs. 2% with placebo) 3
Sexual Dysfunction
- Abnormal ejaculation/orgasm in men (12%) and sexual dysfunction in both men and women 1, 2
- Impotence affects approximately 6% of male patients 2
Other Common Effects
- Sweating/diaphoresis (occurs more frequently with venlafaxine than many other antidepressants) 1, 2
- Anxiety (6%) 2
- Blurred vision (6%) 2
- Weight loss (1%) 2
Serious Adverse Effects
Discontinuation Syndrome
- Abrupt discontinuation can cause withdrawal symptoms including anxiety, irritability, dizziness, electric shock-like sensations, headache, nausea, and insomnia 1, 2
- Symptoms can occur even after missing a single dose due to venlafaxine's short half-life (3-4 hours) 4, 5
- A slow tapering schedule is essential when discontinuing venlafaxine 1, 2
Serotonin Syndrome
- A potentially life-threatening condition characterized by agitation, hallucinations, coma, coordination problems, racing heartbeat, fluctuating blood pressure, fever, nausea, vomiting, diarrhea, and muscle rigidity 1, 2
- Risk increases when combined with other serotonergic medications 2, 6
Psychiatric Effects
- Increased risk of suicidal thoughts and behavior, particularly in children, adolescents, and young adults up to age 24 years 1, 2
- May cause manic/hypomanic episodes characterized by greatly increased energy, severe trouble sleeping, racing thoughts, reckless behavior, and irritability 2
Other Serious Effects
- Low sodium levels (hyponatremia), with elderly patients at greater risk 2
- Abnormal bleeding, especially when combined with blood thinners, NSAIDs, or aspirin 2
- Elevated cholesterol 2
- Seizures (uncommon) 1
- Lung problems (rare) including worsening shortness of breath, cough, and chest discomfort 2
Special Considerations
Overdose Risk
- Venlafaxine overdoses are more frequently fatal than SSRI overdoses 7
- Risk of QT interval prolongation in overdose, which can lead to torsades de pointes 7
Pregnancy and Breastfeeding
- Exposure during the second and third trimesters increases the risk of pre-eclampsia and eclampsia 7
- Some venlafaxine passes into breast milk 2
Drug Interactions
- Contraindicated with MAOIs due to risk of serotonin syndrome 1
- Caution when combined with other serotonergic medications, blood thinners, NSAIDs, or aspirin 2
Monitoring Recommendations
- Regular monitoring of blood pressure and pulse, especially when initiating treatment or adjusting dosage 1
- Monitor for signs of suicidal thoughts, particularly in younger patients 1, 2
- Weight monitoring, as venlafaxine can cause weight loss 1, 2
- Careful monitoring when discontinuing to manage withdrawal symptoms 1, 2