A process for the preparation of an erodible tamper-resistant dosage form that comprises a therapeutic agent-substrate complex embedded in a thermo-formable matrix, such that the complex includes at least one therapeutic agent bound to at least one substrate to form the therapeutic agent-substrate complex. The at least one substrate is being selected from a polyelectrolyte, an organic counter-ion, a pharmacologically inert organic component of a prodrug, an inclusion compound and an inorganic adsorbent; and the thermo-formable matrix includes one or more thermoplastic polymers and optionally at least one pharmaceutical additive. The dosage form provides resistance to intentional or unintentional tampering such as chewing, crushing and grinding, and volatilization.