The potential side effects of supplements in a fitness regimen can vary widely depending on the type and individual reactions. Common issues include gastrointestinal distress, headaches, and allergic reactions. Some supplements might also lead to imbalances in nutrient levels, particularly if taken in excessive amounts. Additionally, certain ingredients can negatively affect heart rate, blood pressure, or even mental health. It is advisable to consult with a healthcare professional before starting any supplementation to ensure safety and appropriateness within one’s overall nutrition and health plan.