An erodible pharmaceutical composition providing a unique zero order controlled release profile contains a therapeutically active substance having a water solubility not greater than 80 mg/mL in water at 25°C, a hydroxypropyl methylcellulose derivative and erosion modifiers depending on drug solubility and drug loading, such as lactose and polyoxyalkylene derivatives of propylene glycol, as well as other inert materials such as binders and lubricants.