This blog is part of a series of blogs linked with BMJ Clinical Evidence, a database of systematic overviews of the best available evidence on the effectiveness of commonly used interventions.

The most common chronic condition worldwide is, or will soon be, multimorbidity. While it was previously a concern reserved for the very old, multimorbidity increasingly affects younger people. A prevalence study in Scotland found that the average middle aged person is no longer a healthy one, but a patient with at least one chronic condition; one in four even had two chronic conditions.

As the population ages, the proportion of people with multimorbidity approaches universality. And as the evidence—often obtained in people with a paucity of comorbidities—gets incorporated into practice guidelines, guideline panels face a key task. Their task is often to provide recommendations on the management of a single chronic condition. So multiple panels take on the task of doing so, each for “their” condition. This approach delegates to frontline clinicians and patients the task of sorting out which recommendations to follow given the priorities and context of the patient.

While sensible, this path is hindered by the translation of guidelines into quality metrics and pay for performance schemes, which reduce the possibility of carefully tailoring the application of the evidence to a particular patient. A review of published guidelines discovered that not only are these disease specific, but also context blind: they tend to remain agnostic as to other comorbidities, patient values and preferences, and patients’ personal and social circumstances. In addition, guideline panels are often overly confident of the net benefit people will experience if they follow their recommendation.

So-called “strong” recommendations denote high confidence in benefit in a manner that is not usually warranted. Strong recommendations, often the result of clear evidence of large benefit and of limited harm and resource use, should be interpreted as ‘just do it” recommendations. Thus, clinicians should be held accountable for following or not following these strong recommendations. In doing so, however, clinicians find a patient with multimorbidity, often living a complex life, in which the right thing to do is seldom clear without involving the patient in shared decision making. Such patient involvement may result in actions that are not consistent with guidelines, and which may suggest poor quality care, when in fact it may reflect the approach of a kind and careful clinician.

Richardson and Doster have offered a simple and helpful framework to understand multimorbidity and how it should clinically affect our confidence in the net benefit of interventions. They propose that interventions could interact with conditions and other interventions, and affect the baseline risk of patient important outcomes, the vulnerability of patients to the adverse effects of treatment, and their responsiveness to interventions.

The possibility of desirable and undesirable effects multiplies as conditions and treatments interact. This should reduce the confidence that clinicians and patients have in deriving net benefit from a particular course of action, and the same should happen to guideline panels. And this may still be true, even when the evidence proves robust across a range of patients with other conditions—a test that has seldom been conducted for common interventions.

Victor Montori is professor of medicine at the Mayo Clinic. He is a practicing endocrinologist, researcher, and author, and also a recognized expert in evidence based medicine and shared decision making. He developed the concept of minimally disruptive medicine and works to advance person centered care for patients with diabetes and other chronic conditions.