ObjectiveThe aim of this cohort study was to gain insight on influencing factors on the decision-making process in conventional medicine compared to complementary and alternative medicine (CAM).MethodsA standardized questionnaire was distributed among cancer patients who attended the counselling facility for CAM of a German university hospital in 2020.ResultsFifty patients (30.3%) returned the questionnaire. After counselling on CAM, most patients made a decision in CAM but also in conventional medicine. Thus, the focus on informed decision-making during counselling on CAM had a strong effect on the decision-making process in conventional medicine. Patients reporting good support also reported making decisions together with physicians and relatives. Moreover, after counselling on CAM, patients reported being more satisfied with their decision in both settings afterwards.ConclusionInformation on CAM which focuses on informed decision-making, supports patient’s ability to understand and weigh risks and benefits of treatments, supports shared decision-making and enables patients to transfer these competences also to decisions on conventional medicine. So counselling on CAM may further decision-making competences in cancer patients. This encourages patients to engage in shared decision-making and increases patient’s satisfaction with decisions.