The medical examiner says Jenna Lord's body sustained significant decay while exposed to the elements.
Officials say the 23-year-old's muscle tissue yielded the presence of drugs including morphine, which they say is consistent with heroin use.
The neighborhood where her body was found on July 18 is known for drug activity.
The Darby, Pa., resident was last seen July 5 following a family barbecue in nearby Collingswood.
Police said the mother of a 3-year-old son got off a train in Philadelphia, returned to Camden and was never heard from again.
The Camden County Prosecutors Office says the physical evidence, along with interviews, make it apparent Lord was not a victim of foul play.