Drug utilization management tools can be employed to ensure that medicines are prescribed cost-effectively, but they can also be implemented in ways that reduce adherence and harm patient health. We examined trends in the prevalence of utilization restrictions on non-protected-class compounds in Medicare Part D plans during the period 2011-20, including prior authorization and step therapy requirements as well as formulary exclusions. Part D plans became significantly more restrictive over time, rising from an average of 31.9 percent of compounds restricted in 2011 to 44.4 percent restricted in 2020. The prevalence of formulary exclusions grew particularly fast: By 2020, plan formularies excluded an average of 44.7 percent of brand-name-only compounds. Formulary restrictions were more common among brand-name-only compared with generic-available compounds, among more expensive compounds, and in stand-alone compared with Medicare Advantage prescription drug plans.