When using heroin, respiration and heart beat slow down, the body temperature slightly drops and the pupils strongly narrow. Opiates decrease the functioning of the intestines and muscles, and sometimes even the sexual needs. First the user can have complaints of throwing up, headache, dizziness, nausea, itchiness and a 'weird' feeling in the head but the active substance doesn't cause damage to tissues and organs. Pain, grief, fear, hunger and cold cannot be felt anymore. The user relaxes and becomes indifferent. The average effect of heroin lasts between 4-6 hours depending on the substance, the dosage and the way it is used.