Factors that may influence teens to abuse drugs is peer pressure, family members, role models and media, improved performance, escape, curiosity, and thrill seeking.
There are many factors as to why teens get into drugs. For example, some teenagers come from broken or abusive households. It's either their parent(s) isn't there or they are afraid to be there at all. Drugs give them time to ignore the problems they deal with on a regular basis. Some people are simply pulled into it, whether by peers or family members. Many teens also suffer from depression and other mental illnesses and use drugs as a means of escape from the effects of their mental illness.
These are just a few examples, but there are certainly many more. Hope this helps you out!
Even though the symptoms of the stimulants and depressants are quite opposite, the causes of these symptoms are completely unrelated. A stimulant could cause one area of the brain to release a chemical and a depressant could affect a completely different area of the brain. They don't have to counteract each other.