OP here. Now it makes sense. Thanks for your clear explanations!

Generics are normally cheaper than brand names (with or without insurance). You will need a prescription for either. Unlike in many other countries, you may not purchase prescription drugs without a prescription. Over-the-counter drugs (like cold medicine etc.) don't require a prescription, but I don't think you are asking about those.

Have you doctor send a generic prescription to your pharmacy. That is your cheapest option. I'm guessing you came from a country where you could get most drugs from the pharmacist. Not so much here and most things require a prescription first (I don't know about Nexium). But yes, just have you doctor send in a prescription saying the generic is fine and the pharmacist will fill it.

You will still need a prescription for generic Nexium and it will be submitted to your insurance. it will be the same "active ingredient" as your brand nexium. You are confusing over-the-counter (medications without prescription) with Brand and generic medications. Brand medications are patented "original" medications. Generics are their chemical equivalents made by a different manufacturer.

In general which one is more expensive, generic medicine from the drugstore or by prescription from your doctor with insurance? I assume it depends on the health plan or type of medicine, but I was wondering if there was a general rule of thumb. Don't know if it's a stupid question, but I'm new to the American health care system. In my case I'm particularly interested in the new generic Nexium coming out verses Nexium I could get by prescription. Thanks!