In general, vitamin C strengthens immunity, and vitamin A improves eyesight
Some mild side effects may occur, such as redness at the injection site or slight nausea
(Generally, most people can supplement with thiamine without prior testing.) The supplements I have taken for thyroid fatigue and recommend are the highly absorbable Benfotiamine by Rootcology, and BenfoMax by Pure Encapsulations
Your heart is working harder to make up for a nutritional shortfall, and that extra effort is what you feel as palpitations
Remember, the duration of efficacy of a B12 shot is an estimate and varies from person to person
Vitamin B12 injections are medically necessary when a patient has severe deficiency, neurological symptoms requiring rapid correction, or a condition that prevents adequate oral absorption