A plastic composition comprising a foraminous matrix of a plastic having particles of a solid drug dispersed in the interstices thereof is produced by coalescing individual particles of a plastic in a compressed mixture of a drug and a plastic which is non-toxic and inert to gastro-intestinal fluids by exposing said mixture to the vapour of an organic solvent for the plastic preferably in a confined space.  The exposure may be carried out at room temperature and atmospheric pressure for a period of 3 to 24 hrs. or at higher temperatures and reduced pressures. Specified plastics are polyethylene, polymethyl methacrylate, copolymers of methyl methacrylate and alkyl acrylates, e.g. methyl acrylate, polyvinyl acetate and polyhexamethylene adipamide. Specified organic solvents are methylene chloride, ethyl acetate, ethylene dichloride, toluene and acetone.  Specified drugs are methamphetamine salts, e.g. the hydrochloride, hexocyclium methyl sulphate, para-amino benzoic acid and its sodium salt, ephedrine, mannitol hexanitrate, amphetamine, erythromycin salts, penicillin salts, pentobarbital, phenobarbital, phenobarbital sodium, atropine, belladonna, theophylline, sex hormones, hydantoins, trimethadione, water soluble vitamins such as B and C, nicotinic acid, benzazoline or toluidine blue O.  The mixture of drug and plastic used in the above method may be prepared by any of the processes described in Specification 833,458.  In order to increase the water permeability of the composition water-soluble excipients such as dextrose acacici, sodium chloride, sucrose, polyethylene glycols, sorbitol, urea, polyvinyl pyrrolidone, inositol, lactose, mannitol, "Methocel" (Registered Trade Mark), calcium chloride and pectin may be added.  Other adjuvants specified are talc and magnesium stearate.ALSO:A prolonged release medicament comprising a foraminous matrix of a plastic having particles of a solid drug dispersed in the interstices thereof, is produced by coalescing individual particles of plastic in a compressed mixture of a drug and a plastic which is non-toxic and inert to gastro-intestinal fluids by exposing said mixture to the vapour of an organic solvent for the plastic preferably in a confined space.  The exposure may be carried out at room temperature and atmospheric pressure for a period of 3 to 24 hours or at higher temperatures and reduced pressures.  Specified organic solvents are methylene chloride, ethyl acetate, ethylene dichloride, toluene or acetone. Specified drugs are methamphetamine salts, e.g. the hydrochloride, hexocyclium methyl sulphate, para-aminobenzoic acid and its sodium salt, ephedrine, mannitol hexanitrate, amphetamine, erythromycin salts, penicillin salts, pentobarbital, phenobarbital sodium, atropene, belladona, theophylline, sex hormones, hydantoins, trimethadione, water-soluble vitamins such as B and C, nicotinic acid, benzazoline or toluidine blue O. Specified plastics are polyethylene, polymethylmethacrylate, copolymers of methyl-methacrylate and alkyl acrylates e.g. methyl acrylate, polyvinyl acetate or polyhexamethylene adipamide.  The mixture of drug and plastic used in the above method may be prepared by any of the processes described in Specification 833,458.  In order to increase the water permeability of the composition water-soluble excipients such as dextrose, acacia, sodium chloride, sucrose, polyethylene glycols, sorbitol, urea, polyvinylpyrrolidone, inositol, lactose, mannitol, "Methocel" (Registered Trade Mark), calcium chloride and pectin may be added. Other adjuvants specified are talc and magnesium stearate.