• you are allergic to any ingredient in Effexor XR
• you are taking or have taken a monoamine oxidase inhibitor (MAOI) (eg, phenelzine), selegiline, or St. John's wort within the last 14 days
• you are taking a fenfluramine derivative (eg, dexfenfluramine), methylene blue, nefazodone, sibutramine, or tryptophan.

Contact your doctor or health care provider right away if any of these apply to you.

Some medical conditions may interact with Effexor XR. Tell your doctor or pharmacist if you have any medical conditions, especially if any of the following apply to you:

• if you are pregnant, planning to become pregnant, or are breast-feeding
• if you are taking any prescription or nonprescription medicine, herbal preparation, or dietary supplement
• if you have allergies to medicines, foods, or other substances
• if you or a family member has a history of bipolar disorder (manic-depression), other mental or mood problems, suicidal thoughts or attempts, or alcohol or substance abuse
• if you have a history of seizures, heart problems (eg, heart failure, irregular heartbeat), abnormal electrocardiograms (ECGs), a recent heart attack, high blood pressure, an overactive thyroid, liver problems, lung problems, kidney problems, stomach or bowel bleeding, blood or bleeding problems, increased eye pressure (eg, glaucoma), nervous system problems, or metabolism problems
• if you are dehydrated, have low blood sodium levels, or drink alcohol
• if you will be having electroconvulsive therapy (ECT).

Some medicines may interact with Effexor XR. Tell your health care provider if you are taking any other medicines, especially any of the following:

• Certain diet medicines (eg, phentermine, fenfluramine), linezolid, lithium, MAOIs (eg, phenelzine), methylene blue, metoclopramide, nefazodone, rasagiline, selective serotonin reuptake inhibitors (SSRIs) (eg, fluoxetine), selegiline, serotonin 5-HT₁ receptor agonists (eg, sumatriptan), sibutramine, SNRIs (eg, duloxetine),St. John's wort, tramadol, trazodone, tricyclic antidepressants (eg, amitriptyline), or tryptophan because severe side effects, such as a reaction that may include fever, rigid muscles, blood pressure changes, mental changes, confusion, irritability, agitation, delirium, and coma, may occur
• Anticoagulants (eg, warfarin), aspirin, or nonsteroidal anti-inflammatory drugs (NSAIDs) (eg, ibuprofen) because the risk of bleeding, including stomach bleeding, may be increased
• Diuretics (eg, furosemide, hydrochlorothiazide) because the risk of low blood sodium levels may be increased
• Azole antifungals (eg, ketoconazole) or cimetidine because they may increase the risk of Effexor XR's side effects
• Cyproheptadine because it may decrease Effexor XR's effectiveness
• Aripiprazole, haloperidol, phenothiazines (eg, chlorpromazine, thioridazine), or risperidone because the risk of their side effects may be increased by Effexor XR.

This may not be a complete list of all interactions that may occur. Ask your health care provider if Effexor XR may interact with other medicines that you take. Check with your health care provider before you start, stop, or change the dose of any medicine.

Important safety information:

• Effexor XR may cause drowsiness, dizziness, or blurred vision. These effects may be worse if you take it with alcohol or certain medicines. Use Effexor XR with caution. Do not drive or perform other possible unsafe tasks until you know how you react to it.
• Do not drink alcohol or use medicines that may cause drowsiness (eg, sleep aids, muscle relaxers) while you are using Effexor XR without checking with your doctor; it may add to their effects. Ask your pharmacist if you have questions about which medicines may cause drowsiness.
• Several weeks may pass before your symptoms improve. Do NOT take more than the recommended dose, or use for longer than prescribed without checking with your doctor.
• Children, teenagers, and young adults who take Effexor XR may be at increased risk for suicidal thoughts or actions. Watch all patients who take Effexor XR closely. Contact the doctor at once if new, worsened, or sudden symptoms such as depressed mood; anxious, restless, or irritable behavior; panic attacks; or any unusual change in mood or behavior occur. Contact the doctor right away if any signs of suicidal thoughts or actions occur.
• Serotonin syndrome is a possibly fatal syndrome that can be caused by Effexor XR. Your risk may be greater if you take Effexor XR with certain other medicines (eg, "triptans," MAOIs, SSRIs). Symptoms may include agitation; confusion; hallucinations; coma; fever; fast or irregular heartbeat; tremor; excessive sweating; and nausea, vomiting, or diarrhea. Contact your doctor at once if you have any of these symptoms.
• Neuroleptic malignant syndrome (NMS) is a possibly fatal syndrome that can be caused by Effexor XR. Symptoms may include fever; stiff muscles; confusion; abnormal thinking; fast or irregular heartbeat; and sweating. Contact your doctor at once if you have any of these symptoms.
• If your doctor tells you to stop taking Effexor XR, you will need to wait for a period of time before beginning to take certain other medicines (eg, MAOIs, nefazodone, thioridazine). Ask your doctor when you should start to take your new medicines after you have stopped taking Effexor XR.
• Effexor XR may rarely cause a prolonged, painful erection. This could happen even when you are not having sex. If this is not treated right away, it could lead to permanent sexual problems such as impotence. Contact your doctor right away if this happens.
• Lab tests, including blood pressure and blood cholesterol levels, may be performed while you use Effexor XR. These tests may be used to monitor your condition or check for side effects. Be sure to keep all doctor and lab appointments.
• Use Effexor XR with caution in the elderly; they may be more sensitive to its effects, especially low blood sodium levels.
• Caution is advised when using Effexor XR in children; they may be more sensitive to its effects, especially increased risk of suicidal thoughts or actions.
• Effexor XR should be used with extreme caution in children; safety and effectiveness in children have not been confirmed.
• Effexor XR may cause weight changes and growth changes. Children and teenagers may need regular weight and growth checks while they take Effexor XR.

Pregnancy and breast-feeding: Effexor XR may cause harm to the fetus if it is used during the last 3 months of pregnancy. If you become pregnant, contact your doctor. You will need to discuss the benefits and risks of using Effexor XR while you are pregnant. Effexor XR is found in breast milk. Do not breastfeed while taking Effexor XR.

Check with your doctor if any of these most common side effects persist or become bothersome:

Abnormal dreams; blurred vision; changes in taste; constipation; decreased sexual desire or ability; dizziness; drowsiness; dry mouth; flushing; headache; increased sweating; loss of appetite; nausea; nervousness; stomach upset; trouble sleeping; vomiting; weakness; weight loss; yawning.

Seek medical attention right away if any of these severe side effects occur:

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); bizarre behavior; blood in the stool; chest pain or discomfort; confusion; decreased concentration; decreased coordination; decreased urination; fainting; fast or irregular heartbeat; fever, chills, or sore throat; hallucinations; memory problems; new or worsening aggressiveness, agitation, anxiety, hostility, impulsiveness, inability to sit still, irritability, panic attacks, or restlessness; persistent or severe ringing in the ears; red, swollen, blistered, or peeling skin; seizures; severe or persistent anxiety, nervousness, or trouble sleeping; severe or persistent cough; severe or persistent headache, dizziness, stomach pain, or weakness; shortness of breath; significant weight loss; suicidal thoughts or attempts; tremor; trouble concentrating; unsteadiness or loss of coordination; unusual bruising or bleeding; unusual or severe mental or mood changes; unusual weakness; vision problems; worsening of depression.

This is not a complete list of all side effects that may occur. If you have questions about side effects, contact your health care provider.