This case-sensitive code system http://hl7.org/fhir/us/davinci-drug-formulary/CodeSystem/usdf-DrugTierCS-TEMPORARY-TRIAL-USE defines the following codes:

Code	Display	Definition
generic	Generic	Commonly prescribed generic drugs that cost more than drugs in the ‘preferred generic’ tier.
preferred-generic	Preferred Generic	Commonly prescribed generic drugs.
non-preferred-generic	Non-preferred Generic	Generic drugs that cost more than drugs in ‘generic’ tier.
specialty	Specialty	Drugs used to treat complex conditions like cancer and multiple sclerosis. They can be generic or brand name, and are typically the most expensive drugs on the formulary.
brand	Brand	Brand name drugs that cost more than ‘preferred brand’ drugs.
preferred-brand	Preferred Brand	Brand name drugs
non-preferred-brand	Non-preferred Brand	Brand name drugs that cost more than ‘brand’ drugs.
zero-cost-share-preventative	Zero cost-share preventative	Preventive medications and products available at no cost.
medical-service	Medical Service	Drugs that must be administered by a clinician or in a facility and may be covered under a medical benefit.