Side Effects of Effexor (Venlafaxine)
Venlafaxine (Effexor) has a higher incidence of nausea and vomiting than other SSRIs and may be associated with increased cardiovascular risks including blood pressure elevation, making it more dangerous than most selective serotonergic antidepressants. 1, 2
Common Side Effects
Venlafaxine commonly causes several side effects that patients should be aware of:
Gastrointestinal effects:
- Nausea and vomiting (most common reason for discontinuation) 1
- Constipation
- Diarrhea
- Dry mouth
- Decreased appetite/anorexia
Neurological effects:
- Dizziness
- Headache
- Somnolence/sleepiness
- Insomnia
- Nervousness/anxiety
- Tremor
Other common effects:
- Sweating (diaphoresis)
- Sexual dysfunction (abnormal ejaculation/orgasm, impotence) 3
- Fatigue/asthenia
- Blurred vision
Serious Adverse Effects
Venlafaxine has several potentially serious adverse effects that require monitoring:
1. Cardiovascular Effects
- Blood pressure elevation: Venlafaxine can cause dose-dependent increases in blood pressure 1, 3
- Increased pulse rate: Approximately 2-3 beats per minute higher than placebo 3
- Risk of QT interval prolongation: Particularly in elderly patients and overdose situations 2
2. Psychiatric Effects
- Suicidality: Increased risk of suicidal thoughts or behavior, especially in children, teenagers, and young adults within the first few months of treatment 3
- Serotonin syndrome: A potentially life-threatening condition with symptoms including agitation, hallucinations, coma, coordination problems, racing heartbeat, high/low blood pressure, sweating, fever, nausea, vomiting, diarrhea, and muscle rigidity 3
- Anxiety and insomnia 3
- Manic/hypomanic episodes: Characterized by greatly increased energy, severe trouble sleeping, racing thoughts, reckless behavior, unusually grand ideas, excessive happiness or irritability 3
3. Discontinuation Syndrome
Venlafaxine has a particularly severe withdrawal syndrome compared to other antidepressants, which can include:
- Anxiety, irritability
- Dizziness, electric shock-like sensations
- Headache, sweating
- Insomnia, nightmares
- Nausea, vomiting, diarrhea 3, 4
Withdrawal symptoms can occur even after missing a single dose due to venlafaxine's short half-life (3-4 hours) 4, 5
Special Considerations
Overdose Risk
Venlafaxine overdoses are more frequently fatal than SSRI overdoses 2
Pregnancy Concerns
Exposure during the second and third trimesters increases the risk of pre-eclampsia and eclampsia 2
Other Serious Risks
- Low sodium levels: Especially in elderly patients 3
- Abnormal bleeding: Especially if taken with blood thinners, NSAIDs, or aspirin 3
- Elevated cholesterol 3
- Lung problems: Including worsening shortness of breath, cough, and chest discomfort 3
- Severe allergic reactions: Including trouble breathing, swelling of the face/tongue/eyes/mouth, rash, itchy welts 3
Monitoring Recommendations
When taking venlafaxine, patients should be monitored for:
- Blood pressure and heart rate (especially at higher doses)
- Signs of suicidal thoughts or behaviors
- Symptoms of serotonin syndrome
- Electrolyte abnormalities, particularly sodium levels
- Sexual dysfunction
- Changes in mood or behavior
Important Precautions
- Never stop venlafaxine abruptly; always taper gradually under medical supervision
- Avoid alcohol while taking venlafaxine
- Be cautious with driving or operating machinery until effects are known
- Do not take MAOIs concurrently with venlafaxine due to risk of serotonin syndrome 1
- Inform healthcare providers of all medications being taken to avoid drug interactions
Venlafaxine's side effect profile is more concerning than most SSRIs, particularly regarding cardiovascular effects and withdrawal symptoms, making it a less favorable choice when other options are available 2, 6.