Although zinc is very important for the human body, excessive intakes can cause serious side effects. Ideally one should not consume more than the maximum allowable value through both food and supplements. Women should not consume more than 11 mg of zinc a day where as this value is 15 mg in men. Daily intakes exceeding 20 mg can be extremely dangerous. Some of the common side effects of zinc supplements are:

• Impaired function of the immune system.
• Improper absorption of iron and interference with its functioning.
• Excessive intakes can lead vomiting and nausea within half an hour of consumption.
• Extra amounts of zinc lead to deficiency in copper.
• Zinc supplements in the form of zinc lozenges can result in mouth irritation, nausea, stomach ache and a bad taste.
• The absorption of various oral quinolones like norfloxacin, levofloxacin, ciprofloxacin and ofloxacin decreases in the presence of excessive zinc as it reacts with NSAIDS which results in reduced absorption of these medicines.

It is best to avoid combining various nutritional supplements like zinc, phosphorus, iron or copper supplements and give a spacing of two hours between each so as to get the maximum benefits of all.