While water-soluble B vitamins are generally considered safe because excess amounts are typically excreted through urine, consuming excessively high megadoses via unmonitored supplementation can present notable health downsides. Over-supplementation of specific B vitamins—such as high levels of niacin causing skin flushing, or excessive pyridoxine (B6) leading to nerve toxicity and numbness—can trigger adverse physiological side effects. Consulting a healthcare professional before starting high-dose regimens ensures appropriate nutritional intake without unnecessary risks.