Effexor Drug Interactions

by on May 11, 2012

Like other medications, Effexor (Venlafaxine) can cause unwanted interactions when taken in conjunction with other drugs. Usually, these drugs affect the metabolism and clearance of Effexor, or the other way around, resulting in increased risk for side effects.

Significant Effexor Drug Interactions

Some of the drugs that can potentially interact with Effexor include:

Anticoagulant Drugs (e.g., NSAIDs, Aspirin, and Warfarin)

Studies have shown that Effexor potentiates the pharmacologic effect of anticoagulants (drugs that interfere with blood clotting. Taking Effexor along with NSAIDs or aspirin increases the risk for bleeding, particularly stomach or intestinal bleeding. Like other SSRIs and SNRIS, Effexor also increases the anticoagulant effect of warfarin hence increasing the potential for bleeding. Patients on anticoagulant therapy should be closely monitored for untoward Effexor side effects.


Cimetidine affects the metabolism of Effexor. Clinical studies show that cimetidine reduces the clearance of Effexor by about half which increases the risk for drug toxicity. However, cimetidine does not appear to increase the pharmacologic effect of Effexor. Most patients do not require dose adjustment. However, patients with high blood pressure, and older adults or those with liver problems, may be given a lower Effexor dose.


Effexor can significantly reduce the excretion of haloperidol thereby increasing blood levels of the drug. This increases the risk for unwanted side effects and even overdose.

Indinavir (Crixivan)

Effexor may reduce the level of indinavir in the blood, potentially making it less effective. Patients taking these medications together may require an adjusted Effexor dosage.

Ketoconazole (Nizoral)

The level of Effexor in the blood may increase when taken along with ketoconazole. This increases the risk for Effexor side effects. Patients taking these medications together may require an adjusted Effexor dosage.

Linezolid (Zyvox), Lithium (Exkalith, Lithobid) and Other Antidepressants (including SSRIs or SNRIs)

These include: Amitriptyline, Zoloft, Lexapro, Effexor, Citalopram, Paxil, Trazodone, Prozac.  These medications can cause serotonin syndrome (a group of symptoms) when taken with Effexor. Contact your healthcare provider if you experience any of these symptoms: confusion, diarrhea, difficulty walking, feeling faint, fever, hallucinations, muscle spasms, rapid heart rate, and sweating. These symptoms can be life-threatening. Do not take these medications without consulting your healthcare provider.

In addition, there are other drugs that can cause serotonin syndrome. Some of these drugs include Tramadol (Rybix ODT, Ryzolt, Ultram, Ultram ER), Acetaminophen (Ultracet), Triptans, and Tryptophan. Meanwhile, taking St. John's Wort along with Effeor can also lead to serotonin syndrome.

Tricyclic Antidepressants

Effexor may increase the levels of tricyclic antidepressants in the blood which can result in unwanted side effects. When taking these drugs together, your healthcare provider may consider adjusting your dose of tricyclic antidepressant to prevent adverse effects.


Effexor tends to reduce the desired pharmacologic effect of metoprolol which is to lower down blood pressure. Furthermore, Effexor has been associated with dose-relate increases in blood pressure therefore caution must be taken when using these drugs together.  It is recommended that patients taking Effexor have regular monitoring of blood pressure. Metropolol dosage may be adjusted, if necessary.

Monoamine Oxidase Inhibitors (MAOIs)

Co-administration of Effexor and an MAOI can cause life-threatening side effects. If you have taken an MAOI over the past two weeks, you should not take Effexor. Also, if you have taken Effexor within the past week, you should not take Effexor.

Preventing Drug Interactions

Inform your healthcare provider if you are taking any of these drugs. However, this drug information guide does not contain all the drugs that can potentially interact with Effexor. Discuss with your healthcare provider drug interactions that apply to you. In addition, patients taking Effexor are highly recommended to avoid taking other medications (including prescription and over-the-counter medications) without consulting their healthcare provider.