B complex vitamins have very few negative side effects when taken under a physician's recommendations. In fact, they are responsible for processing amino acids in the body, which promote cell growth and build the immune system. Nevertheless, if B complex vitamins are taken in too high a dose or if an allergy is present, they can have serious negative side effects.
Vitamin B1
Heart palpitations, insomnia, agitation, high blood pressure, skin eruptions and hypersensitivity can occur if B1 is taken in excess.
Vitamin B2
Overdoses of B2 can cause nausea, vomiting, fatigue, anemia and low blood pressure.
Vitamin B3 or Niacin
Taking too much B3 can cause nausea, vomiting, headaches, flushing of the skin, itchiness and a throbbing head. Try niacinamide as an alternative.
Vitamin B5
Edema, fatigue, joint pain, dehydration and depression are negative of too much B5 in the system.
Vitamin B6
High doses of B6 taken over a long period of time may cause numbness and tingling in fingers and toes as well as loss of muscle coordination. Depression and mood swings have also been known to occur.
B9, or Folic Acid
Side effects of taking too much folic acid can cause kidney damage, nausea, loss of appetite and abdominal bloating.
Vitamin B12
Too much B12 will have such negative side effects as numbness or tingling in the face as well as anxiety.
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