"Schedule III, IV, or V — drugs with an abuse risk less than Schedule II. These drugs also have safe and accepted medical uses in the United States. Schedule III, IV, or V drugs include those containing smaller amounts of certain narcotic and non-narcotic drugs, anti-anxiety drugs, tranquilizers, sedatives, stimulants, and non-narcotic analgesics. Some examples are acetaminophen with codeine (Tylenol® No.3), paregoric, hydrocodone with acetaminophen (Vicodin®), diazepam (Valium®), alprazolam (Xanax®), propoxyphene (Darvon®), and pentazocine (Talwin®)."

This is from a Texas website, but that's about all they have on that type of thing. Schedule 1 are the 'non-legal/medical' drugs, II includes most of the more powerful painkillers.