What is the difference between hydrocodone and hydrocodone bitartrate?

The base is hydrocodone. The salt is bitartrate. If the label does not say bitartrate, then the salt is most likely hydrochloride. The salt makes a difference in how the base is used by your body. The hydrocodone may be absorbed and metabolized faster or slower, and you may have more or less of certain side effects depending on your genes. In either case, they arent much different medications from each other, and the hydrocodone is still there and will work for pain.

There is no difference - hydrocodone bitartrate is the full drug name (of the salt form used in tablets).

I don't think there is a difference. If there is , its not much.