Side Effects of Effexor (Venlafaxine)
Effexor (venlafaxine) has numerous common side effects including nausea, dizziness, insomnia, and increased blood pressure, with potentially serious adverse effects including suicidal thinking, serotonin syndrome, and discontinuation symptoms requiring careful tapering when stopping the medication. 1, 2
Common Side Effects
Gastrointestinal effects: Nausea, vomiting, diarrhea, constipation, abdominal discomfort, dry mouth, and decreased appetite are frequently reported, with nausea being the most common reason for discontinuation in clinical trials 1, 2
Neurological effects: Dizziness, headache, tremor, insomnia, somnolence (drowsiness), and nervousness are common 1, 2
Autonomic effects: Diaphoresis (excessive sweating), which occurs more frequently with venlafaxine than with many other antidepressants 1, 3
Sexual dysfunction: Abnormal ejaculation/orgasm in men and sexual dysfunction in both men and women 1, 2
Weight changes: Decreased appetite and weight loss can occur during treatment 1, 2
Cardiovascular Side Effects
Blood pressure elevation: Venlafaxine can cause dose-dependent increases in blood pressure, with higher risk at doses above 300 mg/day 1, 4
Increased heart rate: Venlafaxine may increase pulse rate by approximately 2-3 beats per minute 2, 3
Hypertension: Sustained clinical hypertension requiring monitoring, especially at higher doses 1
Serious Adverse Effects
Suicidal thoughts and behavior: Increased risk, particularly in children, adolescents, and young adults up to age 24 years 1, 2
Serotonin syndrome: A potentially life-threatening condition characterized by agitation, hallucinations, coma, coordination problems, racing heartbeat, blood pressure changes, fever, nausea, vomiting, diarrhea, and muscle rigidity 1, 2
Discontinuation syndrome: Withdrawal symptoms when stopping venlafaxine abruptly, including anxiety, irritability, headache, electric shock-like sensations, dizziness, confusion, nightmares, nausea, and vomiting - requiring slow tapering when discontinuing 1, 2
Abnormal bleeding: Increased risk, especially when combined with NSAIDs, aspirin, or warfarin 2
Activation of mania/hypomania: Can trigger manic episodes in susceptible individuals 2
Seizures: Though uncommon, venlafaxine may lower seizure threshold 1, 2
Special Populations and Considerations
Pregnancy risks: Exposure during second and third trimesters may increase risk of pre-eclampsia and eclampsia 5
Overdose risk: Venlafaxine may be associated with greater suicide risk than other SNRIs, and both venlafaxine and desvenlafaxine have been associated with overdose fatalities 1, 5
Drug interactions: Concomitant use with MAOIs is contraindicated due to risk of serotonin syndrome. Compared to other SNRIs, venlafaxine may have less effect on the CYP450 system 1, 2
Monitoring requirements: Regular monitoring of blood pressure, pulse, and weight is recommended, especially when initiating treatment or adjusting dosage 1
Comparative Safety Profile
Venlafaxine has a higher incidence of nausea and vomiting than other SSRIs 1
Some studies suggest venlafaxine may be more dangerous than most "selective" serotonergic antidepressants, with higher rates of fatal overdoses compared to SSRI antidepressants 5
Treatment discontinuation due to adverse effects is more common with venlafaxine than with SSRI antidepressants 5