What is the difference between Lortab and Vicodin

They are, just different brand names for hydrocodone/APAP.

They are the same thing...

The active ingredients in these meds are hydrocodone and acetaminophen. They may vary such as 5 mg hydrocodone/500 mg acetaminophen or 7.5/500, etc...

http://www.usdoj.gov/dea/concern/hydrocodone.html

A rose by any other name. Different manufacturer, different name. Another name is Norco.

Different combinations of the drugs:
Vicodin 5/500, 7.5/750, 10/660
Lortab 2.5/500, 5/500, 7.5/500, 10/500
Lorcet 7.5/650, 10/500, 10/650
Norco 5/325, 7.5/325, 10/325
other brand names;
Anexsia, Bancap HC, Ceta-Plus, Co-Gesic, Dolacet, Duocet, Hydrocet, Hydrogesic, Hy-Phen, Margesic-H, Oncet, Panacet, Stagesic, T-Gesic, Vanacet, Zydone....