Every treatment comes with some risk of side effects, but CoQ10, riboflavin, and magnesium have generally been shown to cause minimal side effects, like stomach cramps, bloating, diarrhea, and nausea. People with very serious kidney problems should not take magnesium without a medical provider's supervision. Riboflavin may cause urine to turn a yellow-orange color, but this usually isn’t a cause for concern. If you’re concerned about specific side effects, you might want to talk it over with your provider before starting supplements.