Signs of drug use, abuse and dependence include a decreased sex drive, not caring about clothes or hygiene, and shifts in sleeping or eating habits, according to WebMD. Changes in behavior are more common than physical symptoms when a person is using drugs.
A person using drugs may not care about the future, and he may have an attitude that gets progressively worse, notes WebMD. Drug use can also cause a person's mood to shift erratically, and it may also cause a person to get angry or treat people poorly. Lying, stealing and sneaky behavior may be signs of drug use.
Another sign of drug use is deteriorating relationships with family, states WebMD. Problems with law enforcement, school, work or other authority may be due to drug use. People who are using drugs may be hesitant to introduce new friends to old friends, and they may not keep up with old friends and activities. Behavior changes are not always related to drug use. Other possible causes include stress or depression.
Physical signs of drug use include a dry cough, red eyes and sore throat, notes WebMD. A person who is using drugs may have dilated pupils, and he may have hallucinations. Needle marks on the body, especially the arm, are signs of drug use. A person using drugs may unintentionally lose weight.