Vitamin B12 Side Effects

Vitamin B12 is a water soluble vitamin found in fish, meat and dairy products. It is also found as a man made supplement that can be taken orally or injected. Vitamin B12 is absorbed through the bloodstream. If not properly administered, the vitamin will not fully absorb into the blood during digestion. This can result in Vitamin B12 overdose.

Taken in the correct dosage, it is used by the body to produce nerve and red blood cells and to also avoid b12 deficiency symptoms. Vitamin B12 can also be used to treat deficiency, some forms of anemia and to boost energy. However, it is important to take the right amount to avoid Vitamin B12 side effects that can put your health in danger while making sure you take enough of it to take advantage of the vitamin B12 benefits.


vitamin b12 side effectsA doctor can help eliminate the possibility of Vitamin B12 overdose. A physician will write a prescription for the correct dosage which is based on several factors that include:

  • Your general health
  • The reason you are taking Vitamin B12
  • The form of Vitamin B12 prescribed. Oral and nasal forms of Vitamin B12 have much higher dosages than injections.

Even with taking supplements there is the possibility of a Vitamin B12 overdose so it is always best to stay within the recommended dosage.  People 50 or older should get the majority of their Vitamin B12 from multivitamins, supplements or their diet since they may have problems with absorption.

Recommended Daily Allowance (RDA) of Vitamin B12

Infants up to six months should receive no more than 0.4 mcg in one day since they can easily have a Vitamin B12 overdose. The RDA for babies 7 months to a year is 0.5 mcg; 1 to 3 year olds 0.9 mcg and 4 to 8 years 1.2mcg. School age children 9 to 13 years old should get 1.8 mcg per day; teens and adults over 14 can handle 2.4 mcg without having negative Vitamin B12 side effects. Pregnant women need 2.6 mcg; women who are breastfeed need 2.8 mcg every day.

Some people need vitamin B12 so much that they take B12 injections or they use b12 shots for weight loss reasons since one of the vitamin b12 benefit is how it ups your energy, in fact many energy drinks contain high amounts of it for this reason.

Vitamin B12 Side Effects

Too much of the vitamin can lead to side effects ranging from moderate to life threatening. Milder side effects that might indicate too much of the vitamin includes:

  • Hives
  • Mild Diarrhea
  • Rashes or itching

These Vitamin B12 side effects typically disappear within 24 hours without requiring medical attention.

Although rare, a Vitamin B12 overdose can cause serious health problems such as:

  • Numbness or tingling on the right side of the body
  • Feelings of panic or anxiety
  • Severe allergic reaction

See a doctor immediately if you have any of these or other unusual symptoms after taking Vitamin B12.

Even more rarely, Vitamin B12 side effects lead to such conditions as liver and kidney disease, blood clots or heart trouble.


People with an eye condition known as Leber’s disease should never take Vitamin B12 as it could lead to blindness. Pregnant and breastfeeding women should be extremely cautious to avoid Vitamin B12 overdose since its effects on newborn babies is still unknown.

In general, Vitamin B12 is safe for otherwise healthy people. But as with any vitamin or medication it is best to consult a medical professional if there is any question about dosage or if you have unusual Vitamin B12 side effects.

Could not find what you are looking for? Try a Google Search below:

Leave a Reply