Question

Dwayne has been using heroin for two years. while visiting his mother, he decides to stop. when he stops using the drug, dwayne experiences shaking, irritability, and an inability to concentrate because he is going through ____

Answer 1

Answer: withdrawal

When Dwayne stops using heroin, his brain produces a surge of adrenaline that causes withdrawal symptoms.
The symptoms and the length of that withdrawal, can vary on the drug of abuse and the dwayne's length of the addiction. A heroin withdrawal is very uncomfortable.

Answer 2

The reason is because he is going through "withdrawal".

Human brain works like springs, when with excessive use of drugs one quiets, it bounces back and there are physical effects which show that situation.