Hi, This might be pretty basic, and related to RBC production, but I'd still like to know if it's normal. I am low in iron. Not anaemic, just iron deficient. So I started supplementing it with a tablet that has 100 mg of elemental iron (from ferrous ascorbate) and 1.1 mg of folic acid. Since I had these at home, I started taking them. I also couldn't feel any difference between folic acid and l-methylfolate in my previous experiments with methylation, so I don't say no to folic acid. After my third dose on the third day (taking one a day during lunchtime), the next morning (today) I experienced the following: Profound physical and mental fatigue - unable to get up from bed Drowsiness Muscle spasms Headache Tingling at random places Soon I took some potassium and magnesium citrate, and felt much better in a couple of hours. I know B12 and folate induce a potassium deficiency, but I only take two methyl-b12 1000 mcg tablets in a week, that too orally and not sublingually. This was quite intense, so I thought I should share it here. So I guess one should keep an eye on potassium when supplementing iron, considering RBC production and most of the potassium is required by the new cells? This might be similar to the potassium loss experienced during B12 startup, except iron is using the available B12 in the body, considering there's little supplementation of it.. or maybe I'm just sensitive. Thanks!