Disclosed is a method for preventing the formation of a certain extract of a controlled release matrix formulation comprising a therapeutic amount of an opioid agonist and an opioid antagonist in an amount at least sufficient to substantially antagonize the therapeutic amount of opioid agonist, when both, the opioid agonist and the opioid antagonist, are administered intravenous at the same time, when the controlled release matrix formulation is subjected to a one step extraction procedure comprising the steps of: (a) crushing the formulation of one dosage form using a pill crusher or a tablet mortar, or using two spoons, wherein the crushing is performed at least 4 times using the spoons (b) extracting the crushed formulation of one dosage form on a spoon using 2 ml boiling tap water as extracting agent and a cigarette lighter as heating means for a time period that is necessary to boil the water and (c) filtering the solution using cotton wherein the opioid antagonist is present in said extract to be prevented in a weight percent amount, based on the total amount of opioid antagonist in the dosage form, that is more than 20 %-points less than the weight percent amount of opioid agonist present in the extract, based on the total amount of opioid agonist in the dosage form, and wherein the opioid agonist is oxycodone hydrochloride and the opioid antagonist is naloxone hydrochloride which are present in dosage form in an amount ratio of 2:1,by forming a controlled release dosage form comprising a homogeneous controlled release matrix formulation comprising a hydrophobic material, including at least one hydrophobic polymer being ethyl cellulose and at least one fatty alcohol or fatty acid, being a C12 to C36 aliphatic alcohol or acid and said therapeutic amount of opioid agonist and said sufficient amount of opioid antagonist.
