Described by Isaac Newton in the 1600s, the principle of inertia is one of the fundamental principles of physics and refers to the resistance of an object to change. Applying this principle to the realm of medicine, clinical inertia refers to the failure of healthcare providers to intervene when indicated. The term first used by Phillips et al. at our institution describes the phenomenon that occurs when physicians do not intensify treatment when clinically indicated. Possible explanations for this phenomenon put forth by Phillips et al. include an overestimation of care provided, the use of ‘soft’ reasons to justify nonintervention and a lack of understanding of appropriate clinical guidelines. Some contend that clinical inertia does not adequately represent the complexity of the physician-patient encounter. While inertia implies a failure on the part of the physician to act in patients’ best interest, in actuality, physicians are actively prioritizing the competing demands of patient concerns and symptomatic problems. Reducing this interaction to a checklist of interventions indicated by clinical guidelines minimizes the multifaceted interplay that is the primary care visit. However, many of these arguments seem to reflect resistance in accepting clinical inertia as a problem. Research shows that clinical inertia is a real and measureable problem that adversely impacts patient care. It has been studied most extensively in clinical conditions that are often asymptomatic, associated with significant morbidity and have established treatment guidelines, such as diabetes mellitus and hypertension. In this issue of Drugs & Aging, Gil-Guillen et al. present their study of the factors associated with clinical inertia in patients with hypertension. Utilizing a network of primary care physicians, clinical inertia was identified in 42.1% of patients with poorly controlled hypertension, the majority of whomwere at high cardiovascular risk. Factors associated with clinical inertia include being seen in a primary care setting, the absence of left ventricular hypertrophy or microalbuminuria, the use of combination drug regimens, blood pressure values measured outside the physician’s office, older age and lower blood pressure values. While not designed to prove causation, this study suggests that these factors may play a role when physicians decide whether or not to intensify treatment in patients failing to meet guidelines for adequate control of hypertension. Physicians may be less proactive in blood pressure management in older patients or in patients with blood pressure values that are above goal but not markedly elevated. Physicians may be less likely to initiate new therapy in patients on combination regimens perhaps due to pill burden or lack of available drug options. In addition, physicians may falsely view the absence of end organ damage, such as left ventricular hypertrophy or microalbuminuria, as reassuring. The failure to act on blood pressure values obtained outside the primary care office is especially troublesome. Gathering and integrating information from outside the primary care office is a cornerstone of primary care delivery. Physicians should incorporate this information into management decisions. This study seems to suggest that integration is lacking as perhaps physicians are less cognizant and trusting of that information. This study by Gil-Guillen et al. provides an interesting and novel insight into the problem of COMMENTARY Drugs Aging 2011; 28 (12): 943-944 1170-229X/11/0012-0943/$49.95/0