In this drug factsheet:
What side effects are possible with this medication?
Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent. The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.
The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.
Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.
- abnormal dreams
- changes in taste
- dry mouth
- increased sweating
- loss of appetite
- menstrual changes
- sexual difficulties
- stomach pain or gas
- tingling, burning, or prickly sensation
- trembling or shaking
- trouble sleeping
- unusual tiredness or weakness
- weight loss
Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.
Check with your doctor as soon as possible if any of the following side effects occur:
- changes in vision, such as blurred vision
- increase in frequency of urination or amount of urine produced
- lightheadedness or fainting, especially when rising suddenly from a sitting or lying down position
- mood or mental changes
- ringing or buzzing in ears
- serotonin syndrome (symptoms include confusion, diarrhea, fever, poor coordination, restlessness, shivering, sweating, trembling or shaking, or twitching)
- severe abdominal pain
- signs of liver damage (e.g., yellowing of the skin and eyes, abdominal pain, dark urine, clay-coloured stools, loss of appetite, or nausea and vomiting)
- swelling of the hands or feet (if there is no shortness of breath)
- trouble holding or releasing urine
- unusual or sudden body or facial movements or postures
Stop taking the medication and seek immediate medical attention if any of the following occur:
- attempts at suicide or thoughts of suicide
- chest pain
- convulsions (seizures)
- fast or irregular heartbeat
- muscle pain or weakness
- red or purple patches on skin
- reddening, blistering, peeling, or loosening of skin and mucous membranes
- severe headache upon wakening that is concentrated in the back of the head and neck
- signs of an allergic reaction (e.g., difficulty breathing, hives, swelling of the face or throat)
- swelling of the hands or feet with shortness of breath
Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.
Are there any other precautions or warnings for this medication?
Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.
Allergic reactions: In rare cases, some people may develop an allergic reaction to this medication. Signs of an allergic reaction include a severe rash, swollen face, or difficulty breathing. If these occur, get immediate medical attention.
Behaviour or mood changes: Some people taking this medication experience erratic or aggressive behaviour, agitation, depressed mood, or they may have thoughts of harming themselves or others. If you experience any mood or behaviour changes, or if your friends or family observe any of these changes while you are taking this medication, stop taking this medication and contact your doctor immediately.
Bleeding disorders: Venlafaxine may increase bruising and bleeding from cuts that may take longer to stop. People with bleeding disorders or a history of bleeding problems should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.
Blood pressure: Treatment with venlafaxine has been associated with increases in blood pressure. Your doctor may monitor your blood pressure while you are taking venlafaxine. Rarely, some people may experience a large increase in blood pressure. This extremely high blood pressure can cause rapid or irregular heartbeat, chest pain, dizziness, feeling overly tired, blurred vision, and symptoms of severe headache upon awakening that is mainly in the back of the head and neck region. If any of these symptoms occur, contact your doctor immediately.
Drowsiness/reduced alertness: People taking venlafaxine should use caution when driving or operating machinery until they determine that the medication does not impair their ability to do such activities safely.
Glaucoma: People with glaucoma should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.
Heart disease: People with heart disease should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed. Venlafaxine may cause increased blood pressure or higher cholesterol levels.
Kidney and liver function: People with reduced kidney or liver function should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.
Mania/hypomania: Venlafaxine may cause activation of mania or hypomania. People with a history of bipolar disorder should be closely monitored by their doctor while taking this medication.
Seizures: People with a history of seizure should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.
Serotonin syndrome: This medication may cause a potentially life-threatening condition called serotonin syndrome, especially when used with other medications that increase serotonin levels (e.g., sumatriptan, rizatriptan). If you experience symptoms of serotonin syndrome such as agitation, hallucinations, fast heart rate, fever, lack of coordination, nausea, vomiting, and diarrhea, get immediate medical attention.
Stopping the medication: Stopping this medication suddenly may lead to side effects. If you are thinking of stopping this medication, check with your doctor first. When stopping venlafaxine treatment after more than one week, it is recommended that the dose of the medication be reduced gradually to prevent symptoms such as anxiety, agitation, confusion, diarrhea, dizziness, dry mouth, fatigue, headache, nausea, loss of appetite, nervousness, sleep disturbances, sweating, and vomiting.
Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.
Breast-feeding: This medication passes into breast milk. If you are a breast-feeding mother and are taking venlafaxine, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.
Children: The safety and effectiveness of this medication have not been established for children under 18 years of age. There have been reports that using this and similar medications in children below the age of 18 may cause behavioural and emotional changes, such as suicidal thoughts and behaviour.
What other drugs could interact with this medication?
There may be an interaction between venlafaxine and any of the following:
- anticoagulants (e.g., warfarin)
- antiplatelets (e.g., acetylsalicylic acid [ASA], clopidogrel)
- MAO inhibitors (e.g., tranylcypromine, phenelzine, selegiline)
- nonsteroidal anti-inflammatory drugs (NSAIDs; e.g., ibuprofen, indomethacin, naproxen)
- other serotonin and norepinephrine reuptake inhibitors (e.g., duloxetine)
- selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, fluoxetine, sertraline)
- St. John's wort
- tricyclic antidepressants(e.g., amitriptyline, desipramine, imipramine)
- triptans (e.g., sumatriptan, rizatriptan, zolmitriptan)
- tryptophan supplements
If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:
- stop taking one of the medications,
- change one of the medications to another,
- change how you are taking one or both of the medications, or
- leave everything as is.
An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.
Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.