Zinc supplements can be dangerous when taken in large amounts, though normal amounts are generally safe, according to WebMD. Individuals with diabetes or AIDS should take zinc cautiously, as it may worsen these conditions.
Zinc may cause permanent loss of smell when inhaled through the nose, explains WebMD. Individuals should consider this risk when using nose sprays that contain zinc.
High doses of zinc may cause numerous problems, including stomach pain, fever, fatigue and coughing, according to WebMD. The risk of developing prostate cancer increases by 100 percent if a man takes more than 100 milligrams of supplemental zinc daily or for 10 or more years. Doses of 450 milligrams or more of zinc may cause complications with blood iron, and doses of 10 to 30 grams of zinc can cause death.