Background Polypharmacy is an increasing problem, leading to increased morbidity and mortality, especially in older, multimorbid patients. Consequently, there is a need for reduction of polypharmacy. The aim of this study was to explore attitudes, beliefs, and concerns towards deprescribing among older, multimorbid patients with polypharmacy who chose not to pursue at least one of their GP’s offers to deprescribe. Methods Exploratory study using telephone interviews among patients of a cluster-randomized study in Northern Switzerland. The interview included a qualitative part consisting of questions in five pre-defined key areas of attitudes, beliefs, and concerns about deprescribing and an open explorative question. The quantitative part consisted of a rating of pre-defined statements in these areas. Results Twenty-two of 87 older, multimorbid patients with polypharmacy, to whom their GP offered a drug change, did not pursue all offers. Nineteen of these 22 were interviewed by telephone. The 19 patients were on average 76.9 (SD 10.0) years old, 74% female, and took 8.9 (SD 2.6) drugs per day. Drugs for acid-related disorders, analgesics and anti-inflammatory drugs were the three most common drug groups where patient involvement and the shared-decision-making (SDM) process led to the joint decision to not pursue the GPs offer. Eighteen of 19 patients fully trusted their GP, 17 of 19 participated in SDM even before this study and 8 of 19 perceived polypharmacy as a substantial burden. Conservatism/inertia and fragmented medical care were the main barriers towards deprescribing. No patient felt devalued as a consequence of the deprescribing offer. Our exploratory findings were supported by patients’ ratings of predefined statements. Conclusion We identified patient involvement in deprescribing and coordination of care as key issues for deprescribing among older multimorbid patients with polypharmacy. GPs concerns regarding patients’ devaluation should not prevent them from actively discussing the reduction of drugs. Trial registration ISRCTN16560559 . Electronic supplementary material The online version of this article (10.1186/s12875-019-0953-4) contains supplementary material, which is available to authorized users.