3. What are some internal and external reasons that a teen might use, or decide not to use, heroin? Write at least 3 sentences on this topic that seventh graders could understand.

I'm sorry if this answer is a little long.  you were talking about a very specific drug type so i tried to narrow it down to reasons why teenagers use that drug type plus other things. I hope this helps you out!

Teenagers see lots of people consuming various substances. They see their parents and other adults drinking alcohol, smoking or vaping and sometimes, trying other substances. Also, a teenager’s social scene often revolves around drinking and using marijuana. Sometimes friends urge one another to have a drink or smoke pot, but it’s just as common for teens to start trying a substance because it’s readily available and they see all their friends enjoying it. In their minds, they see drug use as a part of the normal teenage experience. Drugs and alcohol work quickly. The initial effects feel really good. Teenagers turn to drug use because they see it as a short-term shortcut to happiness.

Explanation:  When teens are unhappy and can’t find a healthy outlet for their frustration or a trusted confidant, they may turn to chemicals for solace. Depending on what substance they’re trying, they may feel blissfully oblivious, wonderfully happy or energized and confident. The often rough teenage years can take an emotional toll on children, sometimes even causing depression, so when teens are given a chance to take something to make them feel better, many can’t resist. For example, some teens abuse prescription medicine to manage stress or regulate their lives. Sometimes they abuse prescription stimulants (used to treat attention deficit hyperactivity disorder) to provide additional energy and the ability to focus when they’re studying or taking tests. Others are abusing prescription pain relievers and tranquilizers to cope with academic, social or emotional stress. Teens who can’t tolerate being alone have trouble keeping themselves occupied or crave excitement are prime candidates for substance use. Not only do alcohol and marijuana give them something to do, but those substances help fill the internal void they feel. Further, they provide a common ground for interacting with like-minded teens, a way to instantly bond with a group of kids.