More context: the insulin dose diabetics take with meals is called a bolus dose. However, cells in the human body need glucose uptake constantly, 24 hours a day. So T1 diabetics also have to take a basal insulin dose either once daily as an injection or continuously on a pump. In addition to that, diabetics need to take correction bolus doses to lower their blood glucose when it's high not as a result of a meal, and sometimes they have snack or meals other than just the 3 meals a day. The basal and bolus ratio is around 50% : 50% for some people, although it depends on their doctor and a lot of different factors. So, to recap - there are food boluses, correction boluses, and basal doses.
Here's how I would do the math: 50 units per dose x 3.5 meals on average x 2 for basal = 350 units a day. Or 0.35 vial per day, and 10.7 vials per month. Assuming synthetic human insulin and not insulin analogue is used, that means about $270 per month.
However, some caveats:
- synthetic human insulin is not fast enough for most carbohydrates in meals, and it results in higher blood glucose spikes immediately after a meal than using an insulin analogue. The higher the blood glucose, the more insulin it takes to lower it the same amount. Moreover, we only have so many hours in the day, and slower acting synthetic human insulin needs time to work. So people using it are more likely to "overcompensate" and then eat a bit later to offset their dose. This is a very long-winded way of saying that a person might need slightly more synthetic human insulin than analogues, plus synthetic human insulin in general is less effective.
- In my calculations, I did not include correction bolus doses, insulin used to prime needles, and pump infusion sets (although probably very few people use human synthetic insulin in pumps anyways). I also did not include insulin that is spoiled in some way (refrigerator breakdowns, reserve insulin taken on trips that's not refrigerated, heatwaves, and so on).
- Most people use between 70 and 110 units of insulin per day, whether that's a combination of an insulin analogue and basal insulin injections, or using insulin analogue in a pump. I don't know how much synthetic human insulin is used per day on average, probably a bit more.
So I would say in practice, for someone who uses that much synthetic human insulin, the cost can be even $400 per month. For analogues, it would be much, much higher.
I think it makes sense for me to provide a source for all this - I care for someone with T1 diabetes and am somewhat connected with the broader T1 community.