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Effect of Insulin Price on Medication Adherence in Patients with Diabetes

Jan 12, 2019
Editor: David L. Joffe, BSPharm, CDE, FACA

Author: Michael Zaccaro, Pharm. D. Candidate 2019, LECOM School of Pharmacy

High cost associated with under use in certain patient populations, particularly those with lower incomes.

The incidence of diabetes is increasing, and for many of the patients who are affected, insulin is a necessary and lifesaving medication. It has even been included in the World Health Organization’s “Model List of Essential Medications.” Despite this, the cost of insulin has increased greatly over the past several years. This cost increase has also stimulated a corresponding increase in insurance co-pays and out-of-pocket costs for the patients. It has been shown in previous studies that, in general, medication cost has an inversely proportional relationship to adherence. It is currently unknown if this correlation is applicable to patients’ use of insulin, and little research has been conducted on the topic. The authors of this study hypothesize that insulin cost can affect a patient’s likelihood of adherence to a prescribed regimen. Consequently, the aim of this study is to evaluate the validity of that hypothesis.

An observational study design was selected in order to determine if a correlation exists. The primary outcome of interest was underuse of prescribed insulin regimen due to cost-related reasons. Poor glycemic control due to cost-related underuse of insulin was assessed secondarily. Participants were recruited from a list of individuals who received health services from the Yale Diabetes Center between the months of June and August of 2017. Patients were considered for inclusion if they had been diagnosed with either type 1 or type 2 diabetes and had been first prescribed an insulin regimen at least 6 months prior to the start of the study. No pertinent exclusion criteria were mentioned. Once patients were deemed eligible, they were assessed via a research-validated questionnaire. The questionnaire asks 6 questions that relate to adherence to prescribed insulin regimens and how they relate to cost. Secondary outcomes were assessed using data collected during or within 3 months of their documented visit to the Yale Diabetes Center. Significance was determined via the use of logistic regression.

A total of 354 patients were identified and sent questionnaires. A total of 199 completed the survey and were included in the final analysis. Of the 199 included participants, 81 were diagnosed with type 1 diabetes, 121 were female, and 121 were white. When the information from the questionnaires was analyzed, it was found that 51 (25.5%) reported that high costs resulted in underuse of their prescribed insulin. The cost-related insulin underuse was also shown to be inversely proportional to reported income but not associated with type of insurance coverage. For the secondary outcome, if was found that those who reported cost-related insulin underuse were more likely to have poorly controlled diabetes than those who reported no cost-related insulin underuse (odds ratio of 2.96, p = 0.03).

The results of this study indicate that the out-of-pocket cost of insulin may be associated with nonadherence to prescribed regimens and, consequently, poorly managed diabetes. These findings certainly highlight the need for further, high quality research in the area of medication cost, but also illustrate that more emphasis should be placed on the patient’s ability to afford a medication. For instance, if a small amount of time was to taken to ensure a prescribed medication was formulary preferred for the patient’s insurance or if an assistance / discount program is available for that medication, then it may go a long way toward increasing a patient’s compliance with a prescribed regimen. This is particularly true of more expensive medications such as insulin.

Practice Pearls:

  • The cost of insulin has increased dramatically over the past several years, which translates to higher out-of-pocket costs for patients who use insulin to manage their diabetes.
  • The high cost of insulin is associated with underuse in certain patient populations, particularly those with lower incomes. This underuse translates to decreased diabetes management.
  • Efforts should be undertaken to discuss the cost of medication with the patient and offer assistance when available (i.e., ensuring insulin is on formulary, provide information on manufacturer charity-funded financial assistance programs, offer manufacturer discount cards, etc.).


Herkert, Darby, et al. “Cost-Related Insulin Underuse Among Patients With Diabetes.” JAMA Internal Medicine, Mar. 2018, doi:10.1001/jamainternmed.2018.5008.

Michael Zaccaro, Pharm. D. Candidate 2019, LECOM School of Pharmacy