Too much caffeine can cause nervousness, irritability and sleeplessness, and Zantrex-3 contains 300 milligrams of a mixture of caffeine and caffeine-like stimulants, according to the manufacturer's website. People who are sensitive to stimulants or are taking other medications must consult with their physicians before taking the supplement.
In addition to caffeine, Zantrex-3 contains other stimulants, including yerba mate, green tea and guarana.
The supplement also contains nicotinic acid, according to the Zantrex-3 website, and may cause flushing of the skin in people who are sensitive to niacin. Zantrex-3 is not safe for use by individuals under the age of 18 or women who are pregnant or nursing.
Due to its ability to raise heart rate, Zantrex-3 can damage the heart if used before strenuous exercise, as reported by ABC News. In both young and older people with underlying heart disease, use of the supplement can contribute to bad heart rhythm.
As of 2014, Zantrex-3 is an over-the-counter supplement that is not regulated by the Food and Drug Administration. The overarching effects of Zantrex-3 are largely unknown because it has not been tested for safety or effectiveness, as reported by ABC News. The amount of caffeine and other stimulants can vary from bottle to bottle.