We have presented the main results from various surveys amongst GPs on their pervious experiences and future willingness to participate in clinical studies and cRCTs as a synopsis in the course of this contribution. These findings show GPs to be divided on whether to participate in studies of this type.

Overall, the attitudes of many GPs were notably favourable with regard to the fundamental benefits and added value from clinical research, and that opportunities for corresponding research projects were being taken such as towards identifying and closing healthcare gaps, intensifying application-oriented healthcare research, using evidence-based research instruments and procedures, optimising diagnostic and therapeutic management, and reinforcing multiprofessional healthcare. The research literature repeatedly described methodically embedding primary care into cross-sector, interdisciplinary structures as a major asset in clinical care models [15, 25, 36].

However, some GPs took a more critical and distanced attitude towards long-term goal orientation in corresponding studies. Some respondents were unsure as to what extent structures created by clinical-scientific care models could contribute in practice towards making the healthcare system more effective in the long term. Some expressed uncertainty as to whether primary care could actually benefit from such research participation in the long term.

Urban physicians in the quantitative survey sample [30] identified clear benefits from clinical studies and cRCTs, but their rural counterparts took a more cautious stance. This tallies with the general research findings that GPs in rural areas perceive lower added value in evidence-based structures and instruments [39, 40]. Likewise, most of the 24% of respondents having already taken part in cRCTs were located in urban areas with a greater variety of care services, which is often a prerequisite in effective clinical research [7, 9]. We did not find any significant gender differences in the studies we carried out; this contrasts with other individual studies on willingness of GPs to participate in research networks such as Virnau et al. [2, 42, 43]. Apart from the difference between urban and rural physicians, age is a factor that this study has in common: Openness to clinical research projects amongst the respondents decreased with age [2, 21].

Physicians fundamentally open to or already participating in research projects raised a number of requirements in this regard. Apart from added value for patient care, they emphasised manageable and plannable additional burden, impact on practice routines remaining tolerable, and structural reinforcement in the role of primary care. This tallies with results from previous surveys of primary care research networks (to be established) (see for example: [9, 24, 44,45,46,47,48,49]). A study by Güthlin et al. showed GPs to be especially interested in complex research projects if the topic seemed relevant to them and participation promised an actual benefit for the staff and patients of the practice. With this in mind, it hardly comes as a surprise that physicians having participated in clinical care models give especially favourable assessments of studies on topics such as rural care, drug therapy/safety, delegation, or sector cooperation. Other studies have also shown GPs to consider areas such as polypharmacy, drug safety and adverse drug effects, and multiprofessional cooperation models to be especially important [1, 2, 15, 29, 31]. Apart from that, many GPs currently would not want their medical practice just “researched,” but would rather help shape how these research projects are conducted [44, 45].

The conclusion reached by most of the GPs involved from participation in the corresponding studies is clearly favourable. This applies to healthcare and increase in treatment quality for the patients involved and to the cost–benefit relationship. Physicians found it easier to assess care needs of patients and their relatives, and recommend assistance services. Finally, there was a noticeable increase in subjective capability to perform diagnostics and disease management, and to apply the S3 guideline. Even so, some respondents described negative experiences and stress factors as reflected in documentation requirements and administrative effort, temporary but substantial changes in practice routine, deficits in project communication, and remuneration not matching the effort involved.

The results from the survey may be seen as confirmation of increased willingness amongst GPs to participate in empirical, evidence-oriented studies with the aim of optimising healthcare [15]. Especially younger GPs in urban catchment areas are increasingly basing their work on standardised, evidence-based interventions [39, 40]. Even so, a substantial proportion of general medical practices are fundamentally unwilling or remain reluctant regarding these research projects [1, 7,8,9]. This has resulted in a regional shortage of GPs available for recruitment in complex studies as reflected by project experience from the Innovation Fund in existence in Germany since 2015, often failing to achieve the original target cohorts of physicians and patients [50]. Lech et al. [1] provided one example in a contribution reporting on a cluster-randomised study to optimise outpatient dementia care. The authors reported difficulties in recruiting GPs despite using a wide range of recruitment strategies.

There is mounting evidence that combining these projects with everyday general practice care is not a smooth process, although the reasons for barriers and challenges to recruiting GPs for clinical research have hardly been investigated to date. This involves, on the one hand, immediate difficulties from an underlying shortage of time and resources in general practices [45]. GPs need to make the time required for project activities during consultation hours, which represents a major barrier to any research interest [43, 51]. This barrier may be raised further by the fear of a potentially escalating additional workload such as what GPs see as high-threshold registration of patients for the project, alongside documentation requirements and dealing with complex documentation systems such as digital case files. A low, tightly planned time investment for GPs and their staff always boosts the attractiveness of clinical research and may be of benefit to future recruitment [52]. On the other hand, GPs cast doubts on the match and fit of interventions in everyday primary care. This applies to project plans often conceived from a clinical-scientific perspective that then led to complications and limitations in primary care [44, 45, 49, 50, 53].

A review by Fletcher et al. [3] on GP-based clinical research identified barriers such as poor communication by study coordinators, difficulties experienced by GPs in understanding research methods, concerns about possible harm to patients, and the feeling of being overwhelmed by too many research requests without being perceived as genuine research partners. Routinised communication between all the stakeholders in every project phase plays an especially important role in enabling and improving practice-oriented research [54]. Apart from that, reliable and persistent contacts such as at university hospitals play a major part as an indispensable prerequisite for workable and cooperative relationships between resident GPs and clinical project management [55].

There are also indications that topics covered in clinical research projects do not always match the interests and perceived issues shared by gene, making it impossible to convince them to participate [2, 21, 43, 56,57,58]. This points to the need for continuous interaction between hospital-based primary care and GPs for continuous identification of everyday topics related to healthcare as relevant to GPs and their patients [59,60,61,62].

Beyond the issues already covered, Lech et al. [1] also discussed requirements for a specific recruitment of GPs. The contribution emphasised the benefit of greater concentration on (regional) physicians’ networks to specific recruitment in cRCT studies due to increased research interest, specific topic reference, and close coordination between the participating physicians [47, 63, 64]. A substantial proportion of the physicians involved in the studies were also members of a physicians’ network in the surveys presented [29,30,31, 36, 37].

Finally, consideration should be given to remuneration for participating GPs. GPs and their staff would welcome some financial reward for participating in clinical research even if most do not anticipate major financial losses from time spent in participation. One possibility would be increasing the remuneration amount with the number of patients enrolled into the study [65]. Apart from that, many GPs would benefit from reimbursement of additional expenses; this would help to ensure continuity and sustainability in clinical research networks [63]. Norway provides an example of good practice where physicians participating in research projects receive an annual fee for ongoing administrative work in addition to an hourly fee for each study participation [66].

As shown, the findings obtained the from survey included in this contribution are largely consistent with existing research literature on primary care involvement in clinical research and cRCTs [55, 67, 68]. However, specific weightings and focal points in general practitioner positions as well as additional insights towards motivating GPs to take part in complex clinical research projects emerged during the studies. Figure 2 summarises the central takeaways.

Approaches developed towards optimising integration of primary care in clinical studies (own diagram)

GPs expressed a desire for a manageable and predictable additional workload such as in the complexity of the intervention to be used and in administrative and documentation tasks without excessively interfering with established practice routines [36, 39, 40, 49]. GPs also wished for more individual flexibility in action and decision-making extending beyond participation in research activities to involvement in evidence-based structures and instruments such as disease management programmes and guidelines. Examples of this included authorisation to take alternative approaches considered beforehand in these research projects or temporarily cutting down on project commitment without having to withdraw from the study entirely.

In addition, many GPs also expressed a strong desire for more involvement in shaping project activities and more inclusion in clearly structured communications during research projects. Many GPs advocate constant updates on research-related matters from project management, but also institutionalised, multi-layered exchange and feedback opportunities within the research network. GPs also found it important to use integrated and methodical training programmes and, wherever possible, detailed delegation plans for practice teams to demonstrate possibilities for implementing interventions while saving time and resources as far as possible. All this indicates that clinical research projects have still not always been compatible with the salient primary care setting up to now [16, 44, 53].

GPs saw it as desirable to approach rewards for participation in clinical studies not only in terms of remuneration alone, but also as a form of academic and research recognition. Some respondents saw a definite motivational factor in the possibility of receiving official certification as a university-associated research practice or a specific academic title in recognition of years of commitment to clinical research [44, 47].

Finally, training, and further training as a whole should undergo significant extension towards participation in research studies. The studies performed demonstrated that a sizable proportion of GPs were unsure about their research qualifications and current level of knowledge, leading to doubts as to their personal suitability for active research involvement. Germany has only seen increased efforts towards integrating research competence more firmly as a component of Medical Studies programmes in recent years [1, 37].

The main findings have demonstrated how it might be possible to recruit more GPs in the future. In the opinion of the authors, consistent implementation of these resulting clusters will not only exert a favourable effect on motivation to join but also to remain in the project while also improving process and result quality in cRCT studies. This would also create more favourable general conditions for GPs to take an active part in clinical research in the future. It would also be important to align research projects with topics that GPs see as relevant for these optimisation approaches to materialise, and also to convey the specific benefit and added value for primary care in a clear fashion when addressing physicians [