Like all medicines and supplements, magnesium supplements might also create a number of side effects in people. However, the degree and magnitude of these adverse effects is person specific. Common side effect of magnesium supplement consumption is a drowsy feeling. Mouth of the person might become dry after taking this supplement. Dryness can also be experienced at nose and throat. Mucus of nose can be thickened after its consumption. As a result, the person experiences a dry nose and throat. Nausea and vomiting are also associated with consumption of magnesium supplements. Other commonly observed side-effects are hear burn and mild disorders in stomach. However, consumption of magnesium supplements can create several serious side effects in people. Allergic reactions can marked on skin after consumption of these supplements. The person might feel itching, rash and hives after intake of magnesium supplements. Hence, people with skin allergy history should avoid taking these supplements. Some people witness congestion in chest and difficulty in breathing after consumption of this supplement. Blood in stool or black stool can also be observed in some people after intake of magnesium supplement. Severe stomach pain is also observed in some cases. Unusual tiredness is also a symptom of magnesium supplement consumption.