More than 90% of lung cancer cases are due to cigarette smoking. Nicotine is inhaled or absorbed through the skin. Because nicotine is so addictive, many people return to smoking after quitting, despite the negative consequences. ("Psychology Today") Opioids are classified as drugs that relieve pain. Opioids slow pain signals reaching the brain. They affect an area of ​​the brain that controls emotions, so it also slows down how you think about pain. Some of these drugs would be hydrocodones, morphines, codeines, and oxycodone. (National Institute on Drug Abuse 2014(2)) Stimulants are used to increase energy, otherness, and increase the ability to pay attention. Physical stimulants can increase blood pressure and heart rate. Because stimulants because they are addictive have stopped being prescribed so much. Now, stimulants are prescribed only for ADHD, narcolepsy, and occasionally depression. (National Institute on Drug Abuse 2014 (3)) Illicit drug use usually begins as an experiment. As time passes and the user "experiences" the drug more frequently, he or she begins to rely on the mental or physical effects of these drugs. Furthermore, as time goes by, the user begins to develop a tolerance to the substance and has to use more each time, thus becoming an addiction. Most illicit drugs can make users feel anxious, paranoid, and many may experience hallucinations. (Health line