Taking B complex can affect your sleep, insomnia, I stopped taking them a month or so ago and my sleep has improved. We all think taking vitamins are good for us when some vitamins have the opposite effect and cause insomnia, allergic reactions, rare cases may also experience kidney stones from a high intake of this vitamin combination. Fact is most people do not need to take vitamin supplements and can get all the vitamins and minerals they need by eating a healthy, balanced diet.