We looked at dozens of clinical studies carried out in Europe and the U.S. over the past 30 years, using each of our key ingredients separately in a wide range of doses. After determining the levels at which the ingredients are well tolerated, we evaluated efficacy parameters, including mental alertness and attitudes, sense of well-being, energy level, and sleep patterns.Our recommendation of 2 tablets/day is based on numerous human studies, in which the responses were examined over a range of doses. Our experience is that 2/day is optimal for more than 75% of people. However, some individuals find they obtain a more pronounced effect with a somewhat higher dose (up to 3 or even 4/day) and a few people prefer 1/day. The variation in response to the different doses is clearly related to differences in metabolism and reflects human genetic variability.