The purpose of the study is to determine the relative pharmacodynamic effects and safety of crushed and whole ALO-01 compared to MSIR and to Placebo, and of crushed ALO-01 to whole ALO-01; to determine the relative bioavailability of plasma morphine from crushed and whole ALO-01 compared to MSIR, and from crushed ALO-01 to whole ALO-01; and to determine the relative bioavailability of plasma naltrexone and 6-β-naltrexol from crushed ALO-01 to whole ALO-01.