What is the difference in Adderall ER & Adderall XR?

XR and ER are the same thing!
I was looking for an answer to this question too. I saw the top answers for this post and was frustrated because that would mean my pharmacy messed up my prescription. But through digging a little more I found out that XR *AND* ER are both abbreviations for "extended-release" and are used interchangeably.

Source: https://www.drugs.com/medical-answers/what-does-extended-release-mean-39982/

CR/DR/XR/ER/SR/IR all differ in time lengths. IR is short and even. SR is long but not evenly released. CR isn’t long/short but is released evenly. XR is longer with even releases. ER is similar to XR but shorter. DR is longer but not even. Not all long lasting meds come in capsules and not all short lasting meds are pills/tabs.

Easy way to remember -
IR = Immidiate release (tablet)
XR = Xtended release (capsule)

Any doctor you are asking questions in regards to adderall will be able to give you a straight answer about the two forms of this medication. If they can't, there is something wrong.
I take them both. 30 mg XR in the morning to do it's thing over the course of my day, and then 20 mg IR as a booster around 1:00-2:00 pm to keep me on track for the rest of the day. I have adult ADD/ADHD and this combination works very well for me.

- Just as a side note -
Find a good psycologist or counselor to help you manage your conditions. In my experience they are infinity more helpful and knowledgeable about what medications would best suit your needs. A physicist will only tell you what they want you on. They won't tell you that a pill isn't going fix your problem.
Meds will only get you to a place where you are able to manage your symptoms and identify what work you need to do to take control of them.

Hope all this helps!

The general differences are basically provided by the labels "IR" and "XR." Adderall IR (instant release) is a water soluble pill, and has a fast onset of action (approx. 15-30 min). Adderall XR's (extended release) are capsules with tiny beads inside them, and has a slower onset of action that begins taking effect around 60-90 minutes. Adderall IR's peak effects last only last for approx. 2-4 hours, because it releases the entire dose all at once, which produces noticeably stronger effects. Adderall XR can last anywhere between 6-10 hours, as it releases the dose gradually, resulting in both the physical effects as well as the come down being less noticeable.

They are time release technology XR, ER, SR ( sustained release) are all the same extended release meaning they release the medication not all at once like IR (immediate release).