The present invention provides methods for altering controlled substances in a manner that decreases their potential for abuse. The novel compounds may be combined in tablets with suitable excipients or formulated in solution for oral delivery. When delivered by the oral route the controlled substance is released in a time-dependent manner (sustained release) by acid hydrolysis and/or enzymatic cleavage. When administered by injection the controlled substance is released in a time-dependent manner (sustained release) by way of serum enzymes.