When To Take Vitamin B12?

Vitamin B12 is essential for human health. It helps maintain red blood cells, a healthy nervous system and it promotes the development of young children. It is found almost exclusively in animal products such as meat and eggs. Vegetarians who avoid all animal products in their diet are those most obviously in danger of suffering from a vitamin B12 deficiency. Some vegetarian foodstuffs are 'fortified' with vitamin B12. Unless the vegetarian consumes such products, taking vitamin B12 supplements may be necessary.
Vegetarian mothers who intend to breast-feed their babies are strongly recommended to take B12 supplements to avoid possible complications to the normal neurological development of their children.
Symptoms of vitamin B12 deficiency include anaemia, weight loss, depression, difficulty in maintaining balance, a general sense of fatigue, and tingling or feeling of numbness in the hands.
Aside from vegetarians, those taking certain medications, and those suffering from certain medical conditions, may have difficulty in absorbing vitamin B12 normally from their food, and doctors may advise that supplements be taken.

My father is suffering in Cough regularly and too much cough in early morning after that he will fit after 30 minuts and also facing the breath of veins in lungs.Doctors says that the weakness of veins or etc and consult the injection of Methycabol which have vitamin b12 on regular basis for 20 days.take injec daily in 20 days.i want to know the bad effects of that Injection inother sence the bad reaction.kindly assist me