B12 and B-complex options are common for energy and focus
For example, though vitamin C is unlikely to cause toxicity in healthy people, it can lead to tissue damage and fatal heart abnormalities in those with hemochromatosis, an iron storage disorder ( Side effects related to overconsuming fat-soluble vitamins Because fat-soluble vitamins can accumulate in your bodys tissues, they can cause much more harm when taken at high doses, especially over long periods
Breastmilk contains as much vitamin B12 as the mothers blood so it is especially important for vegetarians and vegans to take supplements during this time, as they are at a much higher risk of deficiency whilst breastfeeding, posing a serious risk for the mother as well as the child (5)
If you experience unexpected symptoms whilst taking B12, discuss with your GP whether continued supplementation is necessary or whether dose adjustment might help
BMC pharmacology & toxicology