The AQ results of this study indicate that 8.9% of all surveyed surgeons used prescription or illicit drugs with the particular intention of CE by AQ. By contrast, the RRT results showed a higher prevalence of 19.9%. Furthermore, using AQ, 2.4% answered that they had already used antidepressants for ME whereas the RRT revealed a prevalence of 15.1%. Furthermore, prescription or illicit drug use for CE or ME was associated with the pressure to perform at work or in private life and with gross income.

On the one hand, there are substantial differences regarding the prevalence rate in the present study. On the other hand, there are significant differences compared with previous studies of drug use for performance enhancement. There are an increasing number of studies dealing with ‘academic performance enhancement’, ‘cognitive enhancement’ or ‘pharmacological neuroenhancement’ regarding cognition (for example, [10, 26, 27, 32, 40–42]).

Regarding prevalence rates and associated factors, it is useful to consider several factors as follows: With the exception of the present study, there exists a severe paucity of data about drug use for CE among employed adults. DAK, a German health insurance company, online surveyed via e-mail 20,000 employed members (20- to 50-years old) with a response rate of 15%. Participants were asked about their use of various substances for CE and mental well-being without medical need [43]. Without accurately distinguishing prescription and over-the-counter drugs, the non-representative DAK study showed a lifetime prevalence rate of 5%. Stated reasons for usage were: ‘depressed mood’, ‘anxiety’, ‘nervousness’, ‘uneasiness’, ‘memory deficits’, ‘fatigue’, and ‘problems of concentration’ [43]. These rationales seem to be the same as among surgeons [1–5]. Furthermore, a non-random online poll by the journal Nature which unfortunately did not specify respondents, demonstrated that 20% of participants had already used prescription drugs for non-medical reasons to improve concentration and improve their focus for a specific task. MPH was the most popular substance, followed by modafinil and beta blockers [32]. MPH and modafinil are also the most prevalently used drugs in our survey. This agrees with the results of our study, although, admittedly, the surveyed groups are not directly comparable. Interestingly, these results match the RRT results of our study. Both surveys, online polls as well as the present RRT study, guarantee a relatively high level of anonymity. This may be one of the most important aspects when assessing pharmacological CE or ME, both potentially highly stigmatizing subjects.

Outside of these particular studies, only students’ substance use for academic performance enhancement has been surveyed. A previous study by our research group among 1,500 high school and university students (over 18 years) using AQ, assessed lifetime prevalence rates of 1.29% for prescription stimulants (MPH, AMPH) and 2.6% for illicit stimulants [27]. Regarding lifetime prevalence, we found that prevalence rates for stimulants in the present study are slightly higher than in our earlier students’ survey. This may be associated with the older age of surgeons.

Furthermore, both studies excluded participants with ADHD or other psychiatric disorders where prescribed psychiatric medications were involved. Many other studies did not exclude these ‘patients’, revealing higher prevalence rates including those where participants misuse their own prescribed medication [40].

A meta-analysis by Wilens and colleagues examining prevalence rates of stimulant misuse included 21 US studies with 113,000 participants revealing a past-year prevalence rate of 5% to 9% in grade and high schools and 5% to 35% in college-age individuals [40]. For this important meta-analysis which included many significant studies about stimulant misuse among students, CE is only a side aspect of the study. This explains the substantially higher (past-year) prevalence rate compared to the present study. However, ‘to concentrate’ and ‘improve alertness’ have been salient participants’ reasons for misuse of stimulants.

The most recent study about CE among 2,600 students using the RRT shows a one-year prevalence rate of 20% for the non-medical use of prescription and illicit drugs for CE [33]. These results show a comparable prevalence to those of the present study.

Beyond that, Partridge and colleagues revealed that a high percentage of the public media portrayed CE as common which accords with our high prevalence rate for CE [42]. However, this finding contrasts with that of our survey study of the same group among university students leading to the assumption of a ‘phantom debate’ [44, 45].

While we were not able to show a significant influence of gender on the use of potential CE- or ME-substances, Dietz and colleagues revealed that significantly more male than female students used prescribed or illicit drugs for CE. Our results do not confirm this finding. The literature is somewhat inconsistent on this subject. For the illicit use of prescription ADHD medications among college students, DeSantis and colleagues found a significantly higher prevalence rate in male than in female students [46], whereas Teter and colleagues found no gender differences regarding prescription stimulant use among college students [47]. However, studies focusing upon this particular association in the context of a different surveyed group from that of the present study, suggest higher risk behaviors in male compared to female subjects [33, 48].

Surveyed surgeons answered that their age of first use of prescription or illicit drugs for CE was 24.0 years. However, our previous study among 1,500 students revealed 17 to 18 years to be the age of first use of prescription or illicit drugs for CE [27]. This is almost 5 to 6 years younger than among surgeons, who themselves had been medical students and later trainee surgeons, decades before. However, study participants are 43 years old (mean) which may imply that two decades ago, the use of CE drugs started substantially later in life. Beyond that, first use of antidepressants for ME was 39 years (mean) compared to an average of 24-year-old participants using CE drugs for the first time.

Methodologically, all these studies only allow an indirect comparison of different survey methods. The present study allows us for the first time to compare AQ questions with RRT questions in one single integrated survey about drug use. In this respect, a previous meta-analysis of 38 RRT validation studies by Lensvelt-Mulders and colleagues reported that RRT provides more valid data than other survey methods. This strengthens the validity of the RRT prevalence rates of 19.9% for CE and 15.1% for ME [49]. This underlines the relevance of the survey method in general. In particular, it strengthens the validity and reliability of the higher RRT results of 19.9% and 15.1% for CE and ME compared to the lower prevalence rates using direct questions.

We were able to show that pressure to perform at work or in private life, together with gross income, are positively associated with the use of prescription or illicit drugs for CE or ME and are the only factors associated with drug use for this purpose. Further hypothesized factors were revealed to play no role in the use of prescription or illicit drugs for CE. We found a positive association of pressure to perform at work or in private life and gross income with the use of drugs for CE. However, we cannot interpret this finding as a general proof of a direct causal relationship between feeling pressure and the use of CE substances. Furthermore, this association is not tenable for professional life in general. Such factors should be addressed in detail in further studies. At least to our present knowledge, there are no data from empirical studies which allow meaningful comparison with our data: studies of students’ drug use focusing on CE as well as the previously cited Nature poll did not examine these factors.

Surgeons should know about the effects and side-effects of the substances used for CE or ME, at least regarding prescription drugs, such as methylphenidate, amphetamine tablets (for example, Adderall®), atomoxetine, modafinil, antidementive drugs and antidepressants. A survey study by Partridge and colleagues showed that university students already seem to have a realistic idea of the effects and side-effects [44]. According to randomized controlled trials (RCTs), reviews and meta-analyses there are almost no pro-cognitive effects regarding normal healthy non-sleep-deprived subjects on simple and higher cognitive domains [12–17].

Nevertheless, stimulants and modafinil have enhancing effects on simple cognitive domains, such as fatigue, vigilance, psychomotor skills and reaction time in sleep-deprived subjects; furthermore, there are slightly pro-cognitive effects on higher cognitive domains and, beyond that, stimulants have subjective ‘pro-effects’ [12, 14, 19–25]. One can presume that the effects on higher cognitive skills are indirect effects which are mediated via simple cognitive skills, for example, vigilance. The fact that sleep deprivation leads to clearer results supports this hypothesis [12].

One would expect surgeons to know these limited effects and to avoid the use of these prescription and illicit drugs for CE. However, every fifth surgeon has already used these drugs. We can only speculate about the reasons. On the one hand, surgeons may not know the missing pro-cognitive effects or overestimate the effects of such drugs. On the other hand, knowledge – and even overestimation – about pro-cognitive effects in sleep-deprived subjects only confirms that sleep deprivation is a common phenomenon among surgeons.

Beyond that, antidepressants (such as SSRI) have no mood enhancing effect in normal healthy subjects at all [12, 18]. Nevertheless, 15% have already used antidepressants for ME, which may indicate missing knowledge about the effects of antidepressants in normal healthy subjects or overestimation of the putative effects.

Another important factor is the side-effect profile and safety risks of amphetamines which have to be considered. Beyond severe side-effects which are described in package-inserts accompanying these drugs and the results of RCTs, reviews and meta-analyses (for example, jitteriness, agitation, cardiologic side effects, such as tachycardia, hypertension, gastro-intestinal side effects, such as stomach ache, diarrhea, and so on), stimulants can cause addiction and further addictive behavior. Also, the misuse of illicit drugs and prescription drugs without prescription is a federal offense.

A number of limitations of the present study are worth identifying here. We obtained a response rate of 36.4% which is a low response rate compared to previous studies using RRT (for example, [27, 33]). However, questionnaires were distributed during conference breaks in huge buildings, so that we were hardly able to control potential participants’ behavior concerning the return of the questionnaires to the black boxes provided. Furthermore, substance use – or even misuse – can be considered a highly stigmatizing subject leading to low response rates. Thus, a response rate of 36.4% may be considered relatively high and comparable to other studies assessing stigmatizing subjects with anonymous questionnaires [36]. However, the response rate of 36.4% together with the non-random sample limits the generalizability of our findings.

Another important factor is the likelihood of a participation bias: Since the response rate is only one third, we do not know in particular whether subjects with more positive attitudes or more negative attitudes on the topic participated disproportionately which may have caused a response bias. Since many more male subjects participated in our study, a potential gender bias exists. This may explain why we did not find gender differences in prevalence rates whereas earlier studies including our own have partly shown that male subjects more often used drugs for CE than female subjects.

Beyond that, we asked surgeons for the non-medical use of stimulants for CE and antidepressants for ME. However, we did not specifically ask for the context of use, for example, whether surgeons had used it directly prior to surgical interventions.