Prevalence of Cognitive and Mood Enhancement Drug Use

The data for this study resulted from a survey conducted in 2011 among 3,306 German-speaking surgeons who attended five international conferences of the German Society of Surgery (Deutsche Gesellschaft für Chirurgie). After the first conference, potential participants were asked if they had been assessed before; those who had been were excluded from a second participation.
Based on previous research about prescription and illicit drugs for CE, an AQ about the use of prescription and illicit drugs for enhancing cognitive functions or mood was developed and distributed to the participants during the conferences. The AQ asked about the ‘non-medical use of stimulants with the particular intention of CE’ and ‘the non-medical use of antidepressants with the particular intention of ME’ during lifetime, last year, last month and last week (frequency). Furthermore, we asked for the age of first use. Beyond that, the AQ included questions about potential risk factors associated with usage of drugs and questions about biometrical parameters (for example, gender, age, age of first use, and so on.). We were mainly interested in healthy participants using drugs specifically for CE or ME. Therefore, the data of participants with self-reported psychiatric disorders (for example, depression, attention deficit/hyperactivity disorder, (ADHD)) who had physicians’ prescriptions for any drug were excluded.
Participants were asked to drop the questionnaire into black boxes after having filled in the questionnaire anonymously.
The study was carried out according to the Principles for Medical Research Involving Human Subjects according to the Declaration of Helsinki. The study was approved by the local Ethics Committee (Landesärztekammer Rheinland-Pfalz) (No. 837.321.08 (6318)). Participants gave informed consent by returning the questionnaire and were informed about this procedure in the introduction section of the questionnaire; this procedure was approved by the above mentioned local Ethics Committee.
The AQ contained questions about the use of drugs for CE and ME as well as questions using RRT. After a brief introduction about the RRT stressing the anonymity of this technique, questions were presented to participants as follows:
Please consider a certain birthday (yours, your mother’s, etc.). Is this birthday in the first third of a month (1st to 10th day)?
If yes, please proceed to Question A; if no, please proceed to Question B.
Question A: Is this birthday in the first half of the year (prior to the first of July)?
Question B: Did you ever use prescription and/or illicit drugs (e.g. Methylphenidate, Modafinil, illicit Amphetamines, and so on) without a medical need for cognitive enhancement?
Note that only you know which of the two questions you will answer
o Yes o No
For assessing the use of antidepressants for mood enhancement, we modified Question B as follows: ‘Did you ever use antidepressants without medical need for enhancing your mood and/or self-esteem, self-presentation?’
The interviewers are not able to know which question the respondent has to answer. Therefore, participants can reply honestly without compromising themselves. Of all participants, 67.1% (245.25/365.25) received the sensitive question (B) and 32.9% (120/365.25) the non-sensitive question (A).
${\widehat{\pi }}_s=\frac{a-\left(1-p\right){\pi }_N}{p}$
the proportion of ‘yes’ responses with respect to the sensitive questions can be estimated from proportion a of total ‘yes’ responses in the sample. p denotes the probability of receiving the sensitive question (Question B; p = 67.1% of all participants received this question). The probability of answering the non-sensitive question (A) with ‘yes’ is π_n = 49.6% (181.25/365.25). A 95% confidence interval (CI) for the unknown prevalence can be computed from the sampling variance
$\mathit{Var}\left({\widehat{\pi }}_s\right)=\frac{a\left(1-a\right)}{n{p}^2}$
where n denotes the sample size [33 (link),39 (link)].
$\begin{array}{l}\begin{array}{l}\mathrm{For}\mathrm{example}\mathrm{for}\mathrm{a}=328/1105\approx 0.30,\\ \mathrm{p}=245.25/365.25\approx 0.67,\\ {\mathrm{\pi }}_{\mathrm{N}}=181.25/356.25\approx 0.50,\mathrm{and}\\ \mathrm{n}=1105,\mathrm{this}\mathrm{yields}\end{array}\hfill \\ {\widehat{\mathrm{\pi }}}_{\mathrm{s}}=\frac{328/1105-\left(1-245.25/365.25\right)181.25/365.25}{245.25/365.25}\hfill \\ \approx 0.1993=19.93\%.\\ {\mathrm{Var}(\widehat{\mathrm{\pi }}}_{\mathrm{s}})=\frac{328/1105\left(1-328/1105\right)}{1105{\left(245.25/365.25\right)}^2}\approx 0.000419.\hfill \\ {\mathrm{SE}(\widehat{\mathrm{\pi }}}_{\mathrm{s}})=\sqrt{0.000419}\approx 0.0205=2.05\%.\hfill \\ \hfill \begin{array}{l}\mathrm{Thus}\mathrm{the}95\%\mathrm{confidence}\mathrm{interval}\mathrm{is}19.93\pm 1.962.05,\mathrm{that}\mathrm{is},\mathrm{ranges}\mathrm{from}\\ 15.91\%\mathrm{to}23.95\%.\end{array}\hfill \end{array}$
Statistical analyses were performed with SPSS for Windows, Version 17.0. Means are given with their corresponding standard deviation (SD) (mean ± SE) and Clopper-Pearson confidence intervals (95% CI). AQ questions were analyzed using a multiple logistic regression analysis. For the regression, the variable selection procedure was performed by using stepwise forward selection with a selection level of 0.05. The variables which were analyzed as potential multivariable predictors of the use of prescription or illicit drugs for CE before forward selection were (available parameters): pressure to perform at work, pressure in private life, gross income, gender, age, family status, living with children, type of employer, employment status, hours of work, satisfaction with professional success, evaluation of career opportunities, pressure to perform subjectively evaluated as burdensome and pressure to perform subjectively evaluated as harmful to health. Ordinal variables with five or more categories (pressure to perform at work, pressure in private life, gross income, pressure to perform subjectively evaluated as burdensome and pressure to perform subjectively evaluated as harmful to health) were treated as continuous variables. Table 1 shows the variables included for the regression after forward selection; all variables which significantly influence the drug use for CE/ ME are listed in this table. There are no further variables for which we adjust. The results are presented as odds ratio (ORs) with confidence limits and P-values. The regression has been analyzed by referring to cases without missing values (complete case analysis).