There are two forms of vitamin A ...prEformed and prOformed ...prOformed comes from carotene sources and cannot be overdosed because the body converts it as needed. However, it's not known how well or even if chameleons can convert it or at least convert it well enough...so we provide a some prEformed to make sure the chameleon gets what we hope is enough in addition to what it gets from the insect diet. PrEformed vitamin A (retinol) can build up in the system though and lead to health issues, so we are careful with it.