According to Dr. Daniel Fenton, clinical director of London Doctors Clinic, suddenly stopping your vitamins can result in various adverse reactions, depending on the individual (via Female First). Dr. Fenton suggests that you should stop taking vitamins if you have a vitamin deficiency. You may feel very fatigued and have a weak immune system. You may develop more serious conditions such as depression if you continue to be deficient for a longer time.
As for how long it will take to feel these effects, Dr. Fenton shares that, “a general rule of thumb, noticeable differences are seen within weeks to months.” Dr. Renee Miranda of the Ohio State University Wexner Medical Center recommends stopping the vitamins one by one, rather than all at once. It is best to stop taking one vitamin for a while and then see how it affects your mood.
You should also consult your doctor if there is a suspicion of a nutrient shortage or if you are considering quitting taking vitamins. Your doctor can advise you on the best steps to take regarding supplements.