Possible side effects of a high dosage of zinc include fatigue, coughing, fever and stomach pain, according to WebMD. Consuming doses of zinc in excess of 450 milligrams each day can create blood iron problems, and consuming 10 to 30 grams of zinc in a single dose can cause death.
Taking zinc in high doses can lower blood sugar levels in diabetes patients, notes WebMD. The likelihood of developing prostate cancer doubles in men who consume more than 100 milligrams of zinc in supplement form or who take it for more than 10 years. The medical community is also concerned that consuming large amounts of multivitamins in addition to supplemental zinc increases the risk of death due to prostate cancer.