However, caution must be exercised in several respects when interpreting the results of this and similar surveys:

(1) Not all non-medical uses of psychotropic drugs serve cognitive enhancement purposes. Few studies on the way students use stimulants differentiate between the interest in better coping with the performance demands of the course and more pleasure-oriented motives of drug abuse.

(2) It should also be checked for each survey whether it covers not only the use of medications but also illegal drugs. Their inclusion is certainly legitimate, in that not only psychotropic drugs obtained without a prescription, but also other stimulants such as cocaine or amphetamine from illegal sources, can be used for cognitive performance enhancement. However, this would result in far higher estimates of the prevalence of neuroenhancement. Appropriate caution should for instance be exercised in interpreting the core result of the largest survey to date on the neuroenhancement practices of German students, according to which 5 % of the respondents should be regarded as brain dopers (cf. module on Studies on the prevalence of cognitive enhancements).

(3) Furthermore, the survey method of studies that intend to investigate the prevalence of neuroenhancement must be considered, as the use of performance-enhancing substances during studies is an ethically and sometimes legally problematic practice. This means that there is a particularly high risk of underestimating the phenomenon due to dishonest responses given by participants. It is consistent with this consideration that the only study to date that has convincingly guaranteed its participants anonymity by using the randomized response method (cf. module on Randomized response) has found a several times higher proportion of students using cognitive enhancement than comparable surveys.

As each study on the prevalence of neuroenhancement has considerable influence on how many participants admit to neuroenhancement, both through the selection of the survey method and the substances in question as well as through the formulation of the relevant mode of use, these surveys are not easily comparable. In particular, it is hardly possible to establish a trend towards neuroenhancement by comparing surveys with different designs conducted at different times.