Tramadol LD50 (Source: Wikipedia)
228 mg·kg (LD50, Ratte, oral)
350 mg·kg (LD50, Maus, oral)
200 mg·kg (LD50, Maus, s.c.)
Vicodin LD50 (Source: Wikipedia)
150 mg·kg (LD50, Ratte, s.c.)
LD50 means that with this amount 50% of experimental animals died. You can estimate how much you need to have a 50% chance that in case the human body reacts similar to the meds you want to OD on.