The first three parts of "The Great Repricing" series broke down how the U.S. biopharma market has split into three distinct payer economies, commercial, government, and self-pay, and what's driving change in each.

This piece tackles the one people understand least: self-pay, or cash.

It's easy to forget that cash payment came first — decades before insurance became the norm. Interestingly, Medicare didn't add a prescription drug benefit until 2006, right around when Walmart's $4 generics reignited the cash market. Today, Avalere and Boston Consulting Group estimate cash transactions make up about 9%-10% of all prescriptions.