Ethanol is the most often abused substance whose primary effect on the CNS varies with blood concentration. Not all individuals experience the same effects at a given blood level. Other CNS depressants have an additive effect when taken in combination with ethanol. At high concentrations, ethanol elimination is relatively constant (zero order). Fatal concentration typically exceeds 0.4 g/dL. Blood concentrations of 0.3 g/dL are associated with coma. Ethyl alcohol is present in many medicinal liquids and mouthwashes. The test is only for screening purpose.