What do harmful use and drug dependence look like?

"Harmful" drug use is drug use that results in risk to self or others (e.g. driving while under the influence, using despite harm to health), interpersonal difficulties due to drug use, financial, occupational or academic problems due to drug use (e.g. failing grades, showing up to work high).   When the drug use shifts to craving, a need for more of the drug to get the same effect , physical symptoms when the drug is no longer being used - then the drug use has shifted into the area of drug dependence. 

The term addiction usually refers to both psychological and physical dependence on a drug, including alcohol. Signs of dependence include withdrawal symptoms (such as depression, anxiety, irritability, cramps, nausea, sweating, and sleeping problems) when we stop using a substance. Another sign is being preoccupied with continuing to use the substance in spite of its negative effect. A third sign is tolerance - the need to use more and more to achieve the same effect.