# Why are some substances (especially medicines) expressed as "units"? **URL:** \ **Category:** Factual Questions\ **Created:** [December 22, 2012, 4:22pm UTC](https://boards.straightdope.com/t/why-are-some-substances-especially-medicines-expressed-as-units/644843 "2012-12-22T16:22:50Z")\ **Posts on this page:** 5\ **Page:** 2
**Author:** ![drewtwo99](https://avatars.discourse-cdn.com/v4/letter/d/d07c76/32.png) [@drewtwo99](https://boards.straightdope.com/u/drewtwo99)\ **Post date:** [December 23, 2012, 4:42pm UTC](https://boards.straightdope.com/t/why-are-some-substances-especially-medicines-expressed-as-units/644843/21 "2012-12-23T16:42:08Z")
> [@Hirka\_T\_Bawa](#): > > In an ideal medical world, the MD/DO would diagnose the disease, the Pharmacist would select the treatment of the disease, and the nurse would administer the treatment… (IMHO of course) Woah. You just blew my mind. Why ARE doctors the one who make the prescriptions? Pharmacists would seem to be much better suited to this task. ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [December 24, 2012, 12:57am UTC](https://boards.straightdope.com/t/why-are-some-substances-especially-medicines-expressed-as-units/644843/22 "2012-12-24T00:57:30Z")
> [@WhyNot](#): > > Related question: is there any insulin that _isn’t_ 100units to 1mL? I haven’t seen it any other way, but we still say dosing in units. Is it just to avoid horrendous microliter =/= milliliter drug errors? The concentrated insulin I take is U-500, and it’s 500 units per mL. I have to take 24 units of it, twice a day, but I have to use a regular U-100 syringe. That way, it’s equivalent to 120 units of U-100, but I don’t have to stick myself twice. When I first brought in the Rx, the pharmacist wouldn’t fill it, because he said it would kill me. Even after calling my doctor, he was still unable to do the math. Another pharmacist had to take over. ---
**Author:** ![Alan\_Smithee](https://avatars.discourse-cdn.com/v4/letter/a/2acd7d/32.png) [@Alan\_Smithee](https://boards.straightdope.com/u/Alan_Smithee)\ **Post date:** [December 24, 2012, 3:32am UTC](https://boards.straightdope.com/t/why-are-some-substances-especially-medicines-expressed-as-units/644843/23 "2012-12-24T03:32:21Z")
That makes absolutely no sense. The whole point of units seems to be that a unit of insulin is a unit of insulin regardless of concentration, so 24 units of U-500 insulin is equivalent to 24 units of U-100 insulin, just in less volume. And using a syringe calibrated for a different concentration seems like a very bad idea, even if the risk of error is low. ---
**Author:** ![Ferret\_Herder](https://avatars.discourse-cdn.com/v4/letter/f/e47774/32.png) [@Ferret\_Herder](https://boards.straightdope.com/u/Ferret_Herder)\ **Post date:** [December 24, 2012, 3:57am UTC](https://boards.straightdope.com/t/why-are-some-substances-especially-medicines-expressed-as-units/644843/24 "2012-12-24T03:57:33Z")
> [@WhyNot](#): > > There are a whole host of abbreviations we’re not supposed to use anymore, because medication errors kills thousands of people every year. At my medical center, “IU” is one of the abbreviations we’re not supposed to use because it can look too much like “IV.” :smack: I forget what the chosen substitute is, pretty sure it’s just “units” or something - it’s not something I run into often. ---
**Author:** ![Speaker\_for\_the\_Dead](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@Speaker\_for\_the\_Dead](https://boards.straightdope.com/u/Speaker_for_the_Dead)\ **Post date:** [December 24, 2012, 11:45am UTC](https://boards.straightdope.com/t/why-are-some-substances-especially-medicines-expressed-as-units/644843/25 "2012-12-24T11:45:50Z")
> [@Ferret\_Herder](#): > > At my medical center, “IU” is one of the abbreviations we’re not supposed to use because it can look too much like “IV.” :smack: I forget what the chosen substitute is, pretty sure it’s just “units” or something - it’s not something I run into often. In both Saskatchewan and New Brunswick, it’s the word “units.” We’re also supposed to avoid “cc” because they can run together to look like a “u”. [Previous page](https://boards.straightdope.com/t/why-are-some-substances-especially-medicines-expressed-as-units/644843.md?page=1)