Résumé : Introduction: In recent year, the role of the pharmacist has evolved from product-focused to patient-focused activities. Following this evolution, new professional pharmacy services were simultaneously developed by researchers and started to be legally implemented and remunerated for community pharmacists around the world. Implementation, essential to ensure a good programme delivery and therefore its effectiveness, was seen as a passive process for which diffusion and dissemination were sufficient to translate research into practice. However, the transition from theory to practice is often difficult as different factors hinder or facilitate the implementation of such services. In consequence of that, implementation research started to be developed in the community pharmacy field to understand and fil the gap between theory and practice.Objectives of the thesis: Three projects were conducted in Belgium and Switzerland; (1) to understand the implementation of an existing programme in Belgium; the isotretinoin pregnancy prevention programme (PPP) (Chapter IV, point 4.1), and (2) to study the implementation of two new developed pharmaceutical services, which include an interview between the pharmacist and the patient and require interprofessional collaboration; the medication adherence program in Switzerland and the medication review in Belgium (Chapter IV, point 4.2). Methods: To understand the implementation of the isotretinoin PPP, two studies were conducted. The first study was a survey sent to health care professionals (pharmacists, general practitioners and dermatologists) and patients. The outcomes of the survey were the PPP awareness and compliance to safety recommendations related to the teratogenic risk of isotretinoin. The second study was cross-sectional and analysed the reimbursed prescription data of the Belgian population taking isotretinoin between January 2012 and August 2015. The outcomes were medication adherence to isotretinoin and to contraception, and the concomitant use of contraception and isotretinoin. Medication adherence was measured using the medication possession ratio (MPR), dividing the total days of medication supplied within the refill interval by the number of days in the refill interval. The concomitant use of isotretinoin and contraception was realised in combining prescription database of both isotretinoin and contraception of women between 12 and 21 years old, who received at least one prescription of isotretinoin during the study period.To study the implementation of the medication adherence program in Switzerland and the medication review service in Belgium, two prospective and observational studies were conducted with a mixed method approach (quantitative and qualitative outcomes). The defined outcomes, based on the RE-AIM model, were; reach of the target patients, adoption of the service by health care professionals providing the service, implementation (facilitators, barriers and fidelity or the extent to which the intervention is delivered as intended), and maintenance (the extent to which the intervention become institutionalized or part of the routine activity). Outcomes were collected through web platforms for quantitative data, and interviews and focus groups for qualitative data.Results and discussion: The study of the isotretinoin PPP implementation showed that two safety recommendations related to the teratogenic risk were particularly poorly applied by interviewed health care professionals. These two recommendations were the use of a second contraceptive method (like condoms) and the monthly pregnancy test. They considered these two recommendations as unnecessary for women taking an effective contraceptive method. Through the prescription refill data analysis, we observed that 46.1% of patients were adherent to isotretinoin (MPR ≥ 0.8) and 74.0% of women taking isotretinoin to their prescribed contraception (oral contraceptive, rings and patches). Lastly, 83.4% of women between 12 and 21 years taking isotretinoin did not receive an effective contraceptive method one month before, during and one month after isotretinoin treatment. However, the proportion of women receiving at least one prescription of contraception during (74.1%) and after (72.1%) isotretinoin treatment was higher than one month before isotretinoin treatment (35.7%). Regarding these results, less adopted recommendations should be reviewed by an expert committee and interventions focused on the improvement of the use of contraception during isotretinoin treatment could be developed.The two studies related to two new developed pharmaceutical services showed that their implementation was feasible in community pharmacy practice. Most of pharmacists participating in both projects had positive attitude regarding the implementation of these services in their daily practice. They considered it as professionally satisfying and important for patients and perceived the benefits of the programs. However, similar barriers were observed; difficulties to include patients and lack of interprofessional collaboration, and lack of time (related to lack of staff, administrative burden and lack of team adoption). According to participating health care professionals, the development of new strategies to overcome these barriers is necessary to anticipate the future implementation and the maintenance of these services at the national level. Following these results, the proposed strategies are for example the development of broad based media campaigns (for health care professionals and patients), or the development of specific trainings focusing on interprofessional collaboration, service-process, practice change management and leadership. Conclusion: The legal evolution of the pharmacists’ role is a positive progress but insufficient to ensure a full implementation in practice. Implementation strategies should be considered at different implementation stages (exploration, preparation, testing, operation and maintenance) and levels (individual, pharmacy, local setting, and system). The use of implementation science would allow a quicker and more effective implementation of these new professional pharmacy services. The anticipation of change and the selection of appropriate strategies would allow a higher fidelity level to the different components of the service by health care professionals and therefore a higher effectiveness, e.g. clinical and economic outcomes. Health care professionals, professional associations, academics and policy makers should be aware of implementation science and integrate it in the development of the new pharmacists’ role. As shown in our results, it should also be considered for existing programmes such as the isotretinoin PPP.