Don't share needles. They can spread AIDS, Hepatitis, and other diseases. Most drugs are safest eaten , less safe smoked, and least safe injected. The more directly the drug is placed in the body, the less chance the body has to detoxify it and remove impurities. The active principle of a drug is the part of the drug that causes the desired effect, in this case, intoxication.
Alcohol is the active principle of beer, for example.
Some drugs, such as tobacco or opium, can cause an addiction in users. Addiction is physical-there is a physical withdrawal if the drug is not used. Dependence is not physical. The user is 'in the habit' of using the drug regularly, or likes doing the drug a lot, but abstinence would not cause physical withdrawal. Other texts use addiction and dependence interchangeably, adding 'physical' to describe classical addiction.