Drug emergencies are not always easy to identify. If you suspect someone has overdosed, or if you suspect someone is experiencing withdrawal, give first aid. Someone who has become addicted to a drug probably won't be able to stop without experiencing withdrawal. Withdrawal is greatly assisted by professional help. Legal prescription drugs are often taken in overdose to achieve effects other than the therapeutic effects for which they were intended.
Some drugs can cause violent and unpredictable behavior.
Get professional help. DO NOT offer your opinions when offering assistance. You don't need to know why drugs were taken to give first aid. DO NOT try to reason with someone who is on drugs. Do not expect them to behave reasonably.