What Are the Causes of Vitamin B12 Deficiency With Effexor?

Effexor, which has the generic name venlafaxine, is an antidepressant used to treat major depression, anxiety and panic disorder. It belongs to a class of antidepressants known as selective serotonin norepinephrine reuptake inhibitors. Vitamin B12 is a water-soluble nutrient that is needed for the synthesis of DNA and red blood cells and also for the maintenance of healthy nerve cells. Effexor and vitamin B12 deficiency are tied together in a couple ways.

Gastrointestinal Upset

Patients taking Effexor might experience common gastrointestinal effects such as nausea, vomiting, stomach pain, diarrhea, gas and heartburn, according to Drugs.com. These side effects can lead to a decreased absorption of vitamin B12 in the body because of frequent vomiting and diarrhea. Vitamin B12 is extracted from food in the stomach with the help of a protein known as intrinsic factor. Intrinsic factor binds to vitamin B12 and helps it get absorbed in the small intestine. Patients experiencing vomiting lose intrinsic factor as well as the vitamin itself.

Unresolved Depression

Patients taking Effexor may experience vitamin B12 deficiency because of malnutrition caused by major depression. Effexor takes a while to relieve symptoms of depression, so even though patients are taking the medication, they might still experience symptoms that cause malnutrition. These include decreased appetite and loss of interest in eating and making healthy food choices.


Untreated vitamin B12 deficiency can lead to pernicious anemia and neurological damage. Symptoms of pernicious anemia include fatigue, shortness of breath, paleness and constipation. Symptoms of neurological damage include numbness and tingling in the extremities, electric-like pain, burning pain, muscle weakness, paralysis and lack of balance and coordination. Patients should ensure that they take prescribed treatments for vitamin B12 deficiency in order to prevent permanent nerve damage. Vitamin B12 deficiency is treated with supplements that are available through injections, tablets and nasal gels.