Magnesium supplements are recommended for people who are deficient in this mineral. The daily recommended dosage of magnesium ranges from 300 to 400 mg per day. If you are taking magnesium supplements, you must also monitor your diet carefully to manage magnesium content. Foods like sea foods, almonds, wheat bran, and green vegetables are rich in magnesium. If your diet is rich in such foods, you will need to take only a small dose of the supplement. On the other hand, if your diet is deficient in magnesium rich foods, you will need to take a higher dosage of the supplement. It is highly unlikely that an overdose of magnesium will harm you. In any case, if you have overdosed on the medication, visit a doctor immediately. Signs of magnesium overdose include dry skin, depression, fatigue, diarrhea, muscle spasms, muscle cramps. Increased levels of magnesium in the body are dangerous especially for people with kidney disease. In such cases, look out for symptoms like blurred vision, coma, change in urination patterns (i.e. decreased or increased urination), slow heartbeat, difficulty in breathing. In most normal, healthy people magnesium overdose will not cause any long term damage or side effects. Always take the supplement as directed by your doctor.