The user is no longer experimenting with the drug; they now feel a need to use it.
Symptoms and signs of drug abuse vary depending on the specific drug, but typically seen across all drugs is the exclusion of activities in order to use the drug. When the person no longer participates in anything but drug use, it is a clear sign of drug abuse. Further decreased performance in work or school and a vast change in mood and sleep are also signs of drug abuse.
Additional signs and symptoms of drug abuse include:
- Unusual, bizarre behavior
- Abnormal vital signs like respiration, heart rate and blood pressure
- Chest or lung pain
- Nausea, vomiting, diarrhea, stomach pain
- Diseases such as hepatitis B or C, or HIV from needle-sharing
- Frequent hangovers
- Hiding drugs
Source : http://www.healthyplace.com/addictions/drug-addiction/signs-of-drug-abuse-symptoms-of-drug-use-and-drug-abuse/