Multiple sclerosis (MS) is a challenging disease characterized by often debilitating symptoms, including pain, fatigue, cognitive impairment, sensorimotor deficits, bowel, and bladder problems, and mental health issues.1 Disease modifying therapies (DMTs), which reduce the rate of disease exacerbations and slow the progress of disease activity, are the cornerstone of MS treatment.1 Consistent use of DMTs has been associated with reduced risk of relapse, fewer inpatient hospitalizations, fewer abnormalities detected by MRI, and lower medical costs.2,3 But despite these improved outcomes, rates of medication adherence are inconsistent and often low.1  

Adherence consists of three distinct domains: acceptance of the illness and need for treatment; continued use of treatment over time (persistence); and compliance with taking the medication as prescribed (the right dose at the right time, and with the right frequency).4 Nonadherence in all three domains is a characteristic of many chronic diseases including MS, and is typically associated with social and economic factors, difficulties with the health care team or system, the characteristics of the disease, disease therapies, adverse events, regimen complexity, and patient-related factors.5,6

 “Adherence” to DMTs is usually defined as a rate of use above 80%, while nonadherence is defined as a rate of less than 80%.1 Adherence has been found to decline steadily over time, with rates between 73% and 79% at six months, 59% to 63% at one year, and 42% to 27% at two years.7 A study of 220 patients treated with subcutaneous interferon (IFN) b-1a, intramuscular IFN b-1a, and glatiramer acetate found an overall adherence rate of 75%, with no significant differences related to the therapy. Adherence was associated with more recently diagnosed MS, lower disability and disability progression, and no treatment changes. Nonadherence was correlated with changes in DMT due to drug ineffectiveness and side effects.8

Factors influencing adherence are listed in Table 1.