During the maintenance of naltrexone narcotic blockade in post- addicts, some patients may at times use non-narcotic abuse drugs, such as barbiturates, amphetamines, methaqualone, etc., as well as alcohol. Animal studies will be undertaken to ascertain that the simultaneous use of these various non-narcotic abuse drugs would not affect either the safety or efficacy of oral naltrexone administered to animals. This would be done by determining the effect of the various abuse drugs on (a) the toxicity of oral naltrexone HCl in mice and rats, and (b) the potency of oral naltrexone HCl in blocking the morphine Straub tail reaction in mice and the morphine loss of righting reflex in rats. Studies would also be made to determine what drugs counteract toxic doses of naltrexone, so as to develop potential antidotes for use in the event of possible overdosage in man.