Taking a daily supplement of 200 mg of magnesium can potentially lead to health problems, especially if you already have kidney issues or are taking certain medications. An excess of magnesium in the blood can cause side effects like a slow heart rate, low blood pressure, dizziness, weakness, and diarrhea. It's important to consult with your doctor before starting a regular magnesium supplement to assess the risks and benefits based on your individual health needs and medication regimen.