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Side Effects of Too High a Dose of Effexor

author image Carole Anne Tomlinson
Carole Anne Tomlinson is a registered nurse with experience in rehabilitation, nutrition, chemical dependency, diabetes and health problems related to the elderly. Tomlinson holds a Bachelor of Arts in criminal justice and is presently working on her master's degree in nursing. Her screenplays have been viewed by Merchant Ivory, Angela Lansbury and Steven King's associates.
Side Effects of Too High a Dose of Effexor
Side Effects of Too High a Dose of Effexor Photo Credit Thinkstock Images/Comstock/Getty Images

Effexor is the brand name of the antidepressant medication known generically as venlafaxine. It falls under the classification of a serotonin and norepinephrine reuptake inhibitor, or SNRI. Effexor helps the two neurotransmitters work more effectively in the brain to reduce mental depression. Effexor also may be prescribed for anxiety and panic disorders, notes MayoClinic.com. Taking too much venlafaxine, whether by accident or because the physician prescribes too high a dosage, causes side effects.

Skin Sensations

Too high a dose of Effexor can cause some unusual skin sensations. For example, the patient may experience sensations of prickling or pins and needles. The skin may feel like it is burning, or it may feel tingly. Emergency treatment is necessary if these side effects are experienced, MayoClinic.com states.


An overdosage-related side effect of Effexor is an acceleration of the heart rate, called tachycardia. This is medically defined as a heart rate exceeding 100 beats each minute without excessive activity. Tachycardia, categorized as an arrhythmia, immediately increases blood pressure. This puts strain on the heart and may cause cardiac arrest or stroke. Any cardiovascular event such as tachycardia classifies as a serious side effect, notes Drugs.com, and requires immediate medical attention.

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Too much Effexor in a patient's body may cause seizures, even if the person has not had a seizure previously. Seizures may occur in the classic form of convulsions, in which the person becomes unresponsive and loses control over the body as it twists and jerks violently. Seizures also may occur in less obvious ways, such as a temporary disassociation with the person's environment. This type of seizure may manifest as a blank stare, and the person may fail to respond to interaction with other people. Immediate medical attention is critical in any case involving a seizure.


Effexor in too high of a dosage may cause extreme weakness throughout the body. The patient may suddenly become very tired, drowsy and sluggish. It may be difficult for the patient to move normally. Once again, immediate medical aid is needed.

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