To date, no toxic effects of carotenoids have been reported. An excessive intake of provitamin A carotenoids i.e., beta-carotene, does not produce vitamin A intoxication, making them a safe sources of vitamin A.
Some research has linked high-dose beta-carotene supplementation over several years with an increased risk of lung cancer and death in heavy smokers and former asbestos workers. The reasons for these findings are not yet clear. As other studies have not shown these effects, it is difficult to interpret the observations. However, supplemental beta-carotene, in doses of 20 mg/day or more, is not recommended for use in smokers (see also Beta-Carotene).
Because of the potential for interactions, dietary supplements should not be taken with medication without first talking to an experienced healthcare provider.