Anyone who consumes too much zinc at one time can end up ill with negative side effects including stomach cramping, vomiting, nausea, loss of appetite, diarrhea and headaches. Long term effects of too much zinc include low copper levels, lowered immunity and low levels of "good" HDL cholesterol, according to the National Institutes of Health. Those who develop severe symptoms to an overdose of zinc should seek medical attention as quickly as possible.
Medline Plus instructs those who think they may have overdosed on zinc to drink milk and seek attention at the nearest medical facility or to call poison control. The National Institutes of Health recommend checking the label of any zinc supplements for dosage information before administering them.
An adult can take 40 mg of zinc per day safely. The National Institutes of Health suggests people use zinc to fight the common cold, to improve the immunity system and heal wounds and to help fight diarrhea and macular degeneration. WebMD reports that some people use zinc for the treatment of ADHD, traumatic head injuries, Crohn's Disease, Alzheimer's and Down Syndrome. All patients should take zinc pills orally and should consult with a physician before taking any type of supplement.