July 7 (Reuters) - Endo International Plc and BioDelivery Sciences International Inc said their experimental pain drug was found effective in a late-stage trial.

The painkiller, BEMA buprenorphine, was being tested against a placebo in patients with pain severe enough to require around-the-clock, long-term opioid treatment.

Opioids are a class of drugs that includes not only powerful prescription painkillers like morphine, oxycodone and fentanyl but also heroin.

(Reporting by Natalie Grover in Bangalore; Editing by Saumyadeb Chakrabarty)