Um...never? It's just been increasing exponentially. There have been consistent increases in the price of insulin since about 2013.
I'm not sure if folks are familiar with the history of insulin, but it's not really one drug: it's a family of different drugs. We started with pork insulin and then human insulin, and now we're into this analogue insulin period of time. The prices of these drugs are increasing in lockstep. Three big pharmaceutical companies control 90% of the insulin market, and there hasn't been a decrease in those prices at all. They control the market and are increasing the prices year over year, exponentially.