Kitt is correct in that generics are supposed to be equivalent in ACTIVE ingredients. BUT they don't necessarily have the same adjuvants (the other junk, like preservatives and fillers), etc. Generic Prevacid, unless labeled 24 hour, or Time Release, is not the same as brand name 24-hour release, only the same as the older procuct which was good for only 10 hours or maybe a little more. (I don't remember what I read in a comparison or PPIs a year or two ago.) The Time Release products are brand new on the markes, so I would highly doubt the generics of that are available yet.
For example - I take time release Toprol XL. Actually I take the generic "ER" now, but I used to have to take the brand name because the generic was not available a few years ago.
Another example - Diprivan. The generic uses sulfite as a preservative. I'm allergic to sulfite, get tachycardia, and have to tell the anesthesiologist. (I put it in writing.)
Some people I know insist on brand name of a few products because the generics do not act properly. One is furosemide a "water" pill. Brand name is cheap for that. Pharmacies are always switching generic brands to find the cheapest (most profitable) one for them. I've had to insist on certain generics over other brands.
There was a big article in Wall Street journal a year or so ago about
generic medicines coming from India, using ingredients coming from China.
Anyway - if you don't get the proper help from the generic you can have the doc write brand name necessary, OR have him prescribe Nexium, which is not available in generic and works better for some people. It's time release 24 hours now, used to work only 18 hours.