What are the side effects of Effexor (venlafaxine)?

Side Effects of Venlafaxine (Effexor)

Venlafaxine commonly causes gastrointestinal effects (particularly nausea), neurological effects, cardiovascular effects (especially dose-dependent blood pressure increases), and sexual dysfunction, with serious concerns including serotonin syndrome, discontinuation syndrome, and increased risk of suicidal thoughts in young adults. 1, 2

Common Side Effects

Gastrointestinal Effects

• Nausea is the most common side effect and the most frequent reason for discontinuation, occurring in up to 37% of patients 2
• Other common gastrointestinal effects include vomiting (6%), constipation (15%), diarrhea (8%), dry mouth (22%), and decreased appetite/anorexia (11%) 2, 1

Neurological Effects

• Somnolence/drowsiness affects approximately 23% of patients 2
• Dizziness (19%), headache (common), insomnia (18%), and nervousness (13%) are frequently reported 2, 1
• Tremor (5%) and abnormal dreams (4%) may occur 2

Cardiovascular Effects

• Dose-dependent increases in blood pressure are a key distinguishing side effect, particularly at doses above 300 mg/day 1, 3
• Risk of sustained clinical hypertension increases with higher doses (3-5% at ≤200 mg/day, 7% at 201-300 mg/day, 13% at >300 mg/day) 4
• Regular monitoring of blood pressure and pulse is recommended, especially when initiating treatment or adjusting dosage 1, 3

Sexual Dysfunction

• Abnormal ejaculation/orgasm occurs in approximately 12% of men 2
• Impotence affects about 6% of men 2
• Sexual dysfunction occurs in both men and women 1

Other Common Effects

• Sweating/diaphoresis (6-19%) occurs more frequently with venlafaxine than many other antidepressants 2, 1
• Anxiety (6%) 2
• Blurred vision (6%) 2
• Weight loss (1%) 2

Serious Adverse Effects

Psychiatric Effects

• Increased risk of suicidal thoughts and behavior, particularly in children, adolescents, and young adults up to age 24 years 2, 1
• Potential for manic/hypomanic episodes, characterized by greatly increased energy, severe trouble sleeping, racing thoughts, reckless behavior, unusually grand ideas, excessive happiness or irritability 2

Neurological Complications

• Serotonin syndrome, a potentially life-threatening condition characterized by agitation, hallucinations, coma, coordination problems, racing heartbeat, high or low blood pressure, sweating, fever, nausea, vomiting, diarrhea, and muscle rigidity 2, 1
• Seizures, though uncommon 5, 1

Discontinuation Syndrome

• Abrupt discontinuation can cause withdrawal symptoms including anxiety, irritability, fatigue, restlessness, sleep problems, headache, sweating, dizziness, electric shock-like sensations, shaking, confusion, nightmares, vomiting, nausea, and diarrhea 2, 1
• Requires slow tapering when discontinuing 1

Other Serious Concerns

• Low sodium levels (hyponatremia), with elderly patients at greater risk 2
• Abnormal bleeding risk, especially when combined with blood thinners, NSAIDs, or aspirin 2
• Elevated cholesterol 2
• Lung problems (rare) including worsening shortness of breath, cough, chest discomfort 2
• Severe allergic reactions including trouble breathing, swelling of the face/tongue/eyes/mouth, rash, itchy welts 2

Special Considerations

Comparative Safety Profile

• Venlafaxine has a higher incidence of nausea and vomiting than other SSRIs 5, 1
• Some studies suggest venlafaxine overdoses are more frequently fatal than SSRI overdoses 6
• Treatment discontinuation due to adverse effects is more common with venlafaxine than with SSRI antidepressants 6

Monitoring Recommendations

• Regular monitoring of blood pressure and pulse is essential, especially when initiating treatment or adjusting dosage 1, 3
• Screening electrocardiogram is recommended for patients older than 40 years with cardiac risk factors 3
• Monitor for signs of suicidal thinking, especially in younger patients 2
• Regular monitoring of weight is recommended 1

Drug Interactions

• Contraindicated with MAOIs due to risk of serotonin syndrome 1
• Use caution when combining with other serotonergic medications, blood thinners, NSAIDs, or aspirin 2
• Venlafaxine has relatively few pharmacokinetic drug interactions compared to some other antidepressants 7

Dosing Considerations

• Side effects are often dose-dependent, with higher doses associated with more noradrenergic effects, including blood pressure elevation 7, 4
• At low doses, the adverse effect profile is similar to an SSRI, while higher doses produce more noradrenergic side effects 7
• Starting at lower doses and gradually titrating up may help minimize side effects, particularly nausea 4

Understanding these side effects and implementing appropriate monitoring can help optimize the risk-benefit profile when using venlafaxine for depression and anxiety disorders.