Ultra Fast Keto Boost Side Effects and unintended effects occurring when the recommended doses are used in humans for prophylactic, diagnostic, therapeutic purposes and for the restoration, improvement or modification of the body's physiological functions. This is the definition adopted by WHO. According to another definition, side effects of drugsthese are harmful and unintended consequences of the use of a medicinal product that result from its authorized use as well as the use of: erroneous, except for the conditions specified in the marketing authorization, misuse, overdose, medical error. All medicines can cause side effects, although not everybody gets them.