All medications have side effects. Hives, constipation, dry mouth, and headaches are common side effects in a lot of drugs. But in some cases certain side effect combinations can indicate an allergic reaction instead of being a side effect. Be sure to read the specific warnings on the drug to be sure.
Vitamin C. Vitamin C is good for your hair growth and healthy skin. Vitamin C may help your skin look younger, according to the Mayo Clinic. Vitamin C plays an essential role in forming collagen. Collagen, a protein, stimulates skin production, according to the National Institutes of Health.
Specific vitamin and mineral deficiencies like iron or vitamin B12 may be diagnosed by blood tests and treated. Multiple vitamins, including biotin, have been promoted for hair growth, but solid scientific studies for many of these claims are lacking. While taking biotin and other supplements marketed for hair, skin, and nails probably won't worsen anything, it may also not necessarily help the situation. Therefore, advertised hair-regrowth supplements should be approached with mild caution.