The medical dictionary defines a side effect as a peripheral or secondary effect, especially an undesirable side effect of a drug or therapy. Vitamin E, taken from food sources alone, doesnt have any documented evidence of any side effects. But vitamin E as a supplement has potential side effects when it interacts with other medications or any other conditions.

Some of the common side effects that may occur due to vitamin E intake are allergic experiences like breathing difficulty, closing of the throat, and swelling of the lips, tongue or face. Some of the less serious side effects are fatigue, weakness, headache, nausea, blurred vision and diarrhea. Usually these side effects stop after stopping the vitamin E intake.

When a vitamin E supplement is taken with other medications for other diseases, there are interactions that are harmful. Vitamin E is known to cause increased risk of hemorrhage in those individuals who take worfin for anticoagulation or those who are deficient in vitamin K. Contradictory results emerge from studies on potential interactions between a combination of antioxidant supplementation (vitamin C, E, selenium and beta-carotene) and cholesterol-lowering agents. A three-year, randomized, controlled trial shows decreased effects of cholesterol-lowering agents and another five-year study shows no effect by the same antioxidant combination.

Vitamin E inhibits the uptake by cells of the antidepressant drug desimpramine, antipsychotic drug chlorpromazine, beta-blockers for high blood pressure and the anti-malarial drug chloroquine.

Increased gamma-tocopherol levels in the blood are associated with a reduced risk of developing prostrate cancer. Vitamin E, when taken in the form of an alpha-tocopherol supplement may lower gamma-tocopherol levels in the blood.

The condition under which the supplement is taken has a significant side effect. When oxidative stress is mild and when vitamin E containing tocopherols is taken alone without other antioxidants like vitamin C, it acts as a pro-oxidant rather than antioxidant because of less generation of free radicals under mild oxidative stress and the absence of vitamin C to neutralize the tocopherol radical. Hence, vitamin E should be taken along with other antioxidants.