Patient adherence: An opportunity for improving outcomes in neurologic diseases

  • Neurological disorders can have significant impacts on costs and the quality of life of patients.
  • Medications are effective disease management solutions, but low adherence is pervasive.
  • Addressing non-adherence rates to treatment reflects a significant opportunity to improve outcomes.

Neurological disorders are a growing burden for healthcare systems worldwide. 

Neurological disorders contributed to 5–10% of the global burden of disease in 2005 (assessed in disability-adjusted life years).1 Conditions such as Parkinson’s disease and epilepsy have significant associated costs and reduced quality of life for patients.2,3 Treatment of these chronic diseases requires patients to incorporate complex medication regimes into their daily routines, putting a significant burden on their lives.4 As the rate of communicable diseases in the developed world has decreased throughout the 20th century (pandemics notwithstanding), public health has begun to put more focus on tackling chronic disease , through prevention and treatment.1

In 2005, disability-adjusted life years per 100,000 population for neurological disorders were highest for lower middle and low income countries (1,514 and 1,448 respectively). These conditions constituted 16.8% of the total deaths in ‘lower middle’ income countries compared with 13.2% of the total deaths in high-income countries.1 The burden can be particularly devastating in lower-income areas, since it can impact ability to work, the cost of medications and requirements for caregiving; international efforts to improve outcomes and quality of life should focus on these populations.1

Medication represents an important solution for improving outcomes and lowering costs.

Medical treatment of epilepsy with first-line antiepileptic drugs may allow up to 70% of patients to remain seizure-free.1 A study in Brazil found that non-adherence to epilepsy medication was linked to younger age and male gender, and that strategies to improve treatment adherence must understand the needs of these populations.4 A UK study found that a household in the UK where someone has Parkinson’s disease is, on average, more than £16,500 worse off per year.5 Non-compliance with Parkinson’s disease medications may result in a poor response to therapy, and ultimately increase direct and indirect healthcare costs.6 A review of U.S databases found that the estimated total annual economic burden of bipolar disorder was more than $195 billion, with approximately 25% attributed to direct medical costs, with individuals using healthcare services frequently. Suboptimal medical adherence was found to be a driver of higher direct costs.7

Successfully managing neurological disorders requires extreme consistency in patient adherence behavior. How is adherence defined?

Medication adherence is defined as “the degree to which the person’s behavior corresponds with the agreed recommendations from a health care provider”, and is considered to have three components, commonly referred to as fulfillment, persistence and compliance.8

  • Fulfillment refers to the treatment prescription being filled by the patient.8
  • Persistence refers to the treatment being taken for the intended duration.8
  • Compliance refers to the intended treatment regimen, including intended timing and dosage.8

Adherence is complex; maintaining high adherence levels requires that patients continuously make choices and adjust their behavior to overcome the various challenges to taking their treatment.

Medication adherence is defined as “the degree to which the person’s behavior corresponds with the agreed recommendations from a healthcare provider.”

How is adherence measured in the real world?

The complexity of patients’ behavior regarding their medication makes real adherence levels and impact difficult to quantify. Proxies developed to assess adherence in real-world studies include the mean Medication Possession Ratio (MPR) and the Proportion of Days Covered (PDC).9

  • Medication Possession Ratio is commonly defined as “the proportion (or percentage) of days’ supply obtained during a specified time period or over a period of refill intervals” and can be calculated using various methods.9
  • Proportion of Days Covered allows to go further as it refers to the total number of days’ supply dispensed during the study period divided by the number of days in the study period.9

Poor treatment adherence is pervasive, particularly in developing countries.

Adherence in the case of any individual patient via either of these measures is generally defined as a ratio of at least 80%.10 Studies indicate a global adherence rate of approximately 50%, meaning that roughly half of prescribed medications are not taken, with non-adherence rates expected to be even higher in developing countries.11,12

Adherence remains a significant opportunity area for improving outcomes

Estimated adherence rates vary across chronic neurological disorders; for Parkinson’s disease, sub-optimal adherence varies between 10 and 67%, with lower adherence associated with complex regimens.3 Compliance is particularly important due to the condition’s progressive and debilitating nature, and the lifelong need for medication.6 Non-adherence rates of up to 50% have also been reported in conditions such as epilepsy and bipolar disorder.4,13 Low adherence to pharmacological treatments for other chronic conditions is linked to poor control of disease risk factors, increased risk of mortality, and extremely high per patient costs.10 Adherence represents an important opportunity that must be addressed.


  1. World Health Organization. Neurological Disorders: Public Health Challenges. 2006. Available at: [Accessed March 2021].
  2. Moura LMVR, et al. Patient-reported financial barriers to adherence to treatment in neurology. ClinicoEconomics and Outcomes Research 2016;8:685–94.
  3. Straka I, et al. Adherence to Pharmacotherapy in Patients With Parkinson’s Disease Taking Three and More Daily Doses of Medication. Frontiers in Neurology 2019;10:799.
  4. Ferrari CMM, et al. Factors associated with treatment non-adherence in patients with epilepsy in Brazil. Seizure 2013;22:384–9. 
  5. Parkinson’s UK. The cost of Parkinson’s: the financial impact of living with the condition. 2017. Available at: [Accessed March 2021].
  6. Malek N and Grosset DG. Medication adherence in patients with Parkinson’s disease. CNS Drugs 2015;29(1):47–53.
  7. Bessonova L, et al. The Economic Burden of Bipolar Disorder in the United States: A Systematic Literature Review. ClinicoEconomics and Outcomes Research 2020;12:481–97.
  8. Jimmy B and Jose J. Patient Medication Adherence: Measures in Daily Practice. Oman Medical Journal 2011;26(3):155–9.
  9.  Raebel MA, et al. Standardizing Terminology and Definitions of Medication Adherence and Persistence in Research employing Electronic Databases. Med Care 2013;51:S11–S21.
  10. Anghel LA, et al. An overview of the common methods used to measure treatment adherence. Med Pharm Rep 2019;92(2):117–22.
  11. Brown MT and Bussell JK. Medication Adherence: WHO Cares? Mayo Clin Proc 2011;86(4):304–14.
  12.  World Health Organization. Adherence to Long-Term Therapies: Evidence for action. 2003. Available at: [Accessed March 2021].
  13. Jawad I, et al. Medication nonadherence in bipolar disorder: a narrative review. Ther Adv Psychopharmacol 2018;8(12):349–63.