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Venlafaxine (Effexor XR) was introduced as an antidepressant, although it is sometimes used to treat other mental conditions such as panic disorder. Venlafaxine is classified as an SNRI-a serotonin-norepinephrine reuptake inhibitor. That puts it in the same category as duloxetine (Cymbalta) and desvenlafaxine (Pristiq). These medications affect many systems of chemical messengers (the neurotransmitters serotonin, norepinephrine and dopamine) in the brain.

Side Effects and Interactions

The side effects of venlafaxine include nausea, headache, anxiety or agitation, insomnia, drowsiness, excessive sweating and loss of appetite. Appetite problems may result in weight loss, but venlafaxine is by no means a weight-loss drug.

Dry mouth, dizziness, constipation, tremor and blurred vision are other possible side effects. Venlafaxine may lead to increased blood pressure in some people, so blood pressure should be monitored on a regular basis. Blood cholesterol levels may also rise while a person is taking venlafaxine. Excessive sweating or yawning, exhaustion, rapid heartbeat and abnormal dreams are among the common reactions, as are sexual difficulties such as erectile dysfunction and ejaculatory problems.

Serious Reactions of Venlafaxine

Venlafaxine carries a black box warning to alert prescribers, patients and their families that those taking the drug may be at increased risk for committing suicide. This risk is strongest for young people 24 years old or less. The drug is not approved for use in children.

As with other antidepressants, people taking venlafaxine may find their depression worsening or experience manic symptoms.

Some patients on venlafaxine have experienced seizures. Report any symptoms or suspected side effects without delay.

Pancreatitis, liver damage and severe skin reactions that may require hospitalization are among the rare but serious problems that may be triggered by venlafaxine. Hyponatremia (a dangerously low sodium level), heart rhythm disturbances and excessive bleeding have also been reported.


Stopping venlafaxine suddenly can result in symptoms such as nausea, diarrhea, digestive distress and visual disturbances. Dizziness and vertigo may be accompanied by a feeling variously described as “head in a blender” or “brain sloshing.” Many people who stop venlafaxine suddenly also complain of “brain zaps”-sensations like electric shocks to the head. Headaches, anxiety, tremors and nerve tingling or other strange sensations can be very unsettling. Anxiety and irritability are common withdrawal reactions, as are extreme fatigue. This discontinuation syndrome can be disabling. Sudden withdrawal should be avoided if at all possible; unfortunately, doctors do not have adequate instructions on how slowly people may need to decrease the dose of this medication.


Because of the possibility of a life-threatening interaction called serotonin syndrome, venlafaxine must not be taken by anyone on an MAO inhibitor such as isocarboxazid, phenelzine, procarbazine, selegiline or tranylcypromine. Other drugs that inhibit monoamine oxidase and must be avoided include the antibiotic linezolid (Zyvox) and methylene blue injections.

A person who has been taking an MAO inhibitor should wait at least 14 days after stopping it before beginning to take venlafaxine; after stopping venlafaxine, a person should wait 7 days before starting on an MAO inhibitor.

Certain medications, particularly amiodarone (Cordarone), dronedarone (Multaq) and thioridazine can increase the possibility of QT prolongation, a potentially deadly change in heart rhythm, and should not be taken in combination with venlafaxine.

Other Drugs That React Badly with Venlafaxine

antidepressants such as citalopram (Celexa),

antipsychotic drugs such as asenapine (Saphris),

cancer treatments such as crizotinib (Xalkori),

migraine headache medicines such as almotriptan (Axert), eletriptan (Relpax), frovatriptan (Frova), naratriptan (Amerge), sumatriptan (Imitrex) and zolmitriptan (Zomig)

hepatitis C medications such as boceprevir (Victrelis),

HIV drugs such as cobicistat (Stribild)

quinine derivatives such as chloroquine,

special-use antibiotics such bedaquiline (Sirturo),

et can slow removal of Effexor from the body, and a person who must take both may need a dosage adjustment. This is most likely to affect individuals with high blood pressure or liver problems, and the elderly.

Certain other medications, such as quinidine, may increase blood levels of Effexor, but there is limited data on interactions, and there may be other drug interactions that have not yet been identified.

Ask your doctor and pharmacist to check whether any other drug or herb you take is safe in combination with Effexor.

Special Precautions

Venlafaxine can cause or exacerbate narrow-angle or angle-closure glaucoma and should not be given to anyone with this eye condition.

Some depressed people experience anxiety and insomnia as part of the symptoms of their condition. Effexor may exacerbate these problems in some patients.

The drug may also worsen the manic phase for some manic-depressive individuals and not be appropriate for continued treatment.

Any medicine affecting the brain may have the potential to slow reflexes or impair judgment. Such problems did not appear significant in clinical trials, but patients are best advised not to drive or use hazardous machinery until they can determine (preferably through an objective assessment) that they are not adversely affected by Effexor.

As of this writing, Effexor is a new drug with relatively little data available. Studies have not established that it is effective for long-term use of more than six weeks. It is advisable for doctor and patient to reevaluate this therapy periodically to make sure that it continues to be appropriate.

Taking the Medicine

Effexor should be taken with food. The dosage should be individually adjusted and will determine whether Effexor is taken two or three times daily. When going off Effexor, a person should ask the doctor for guidelines on gradual withdrawal.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.” .
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