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.
Overall, the entire suite of B-complex vitamins is essential for good hair and skin. In addition to Vitamin B12, vitamins B3 and B6 are also critical for hair and skin growth and appearance. A balanced B-complex vitamin supplement provides the extra boost your hair and skin may need to look great.
1 Free radical damage can cause hair aging, and vitamin C can help protect the scalp and fair follicles from this major hair growth inhibitor.  Biotin and pantothenic acid (vitamin B5) have been used as alternative treatments for hair loss. Biotin rebuilds hair shingles, and vitamin B5 supports the adrenal glands.