When we become a Christian we are born again. Reborn, but spiritually. From that point on we begin to change for the better. To become a different person under God's influence. In the Bible a man called Nicodemus didn't understand when Jesus said "Most assuredly I say to you, unless one is born again, he cannot see the kingdom of God." That's in John 3:3 (New Testament). It means John chapter 3 verse 3.
So Nicodemus said. He knew we are all born once only in a physical way from our mother's womb. Jesus meant we must be born again spiritually. We begin to change as we allow God's Holy Spirit to begin working.
A drug addict can be a powerful witness for Christ. Many have become pastors. So have former alcoholics. Prostitutes have become Sunday School teachers. They are living examples of being born again by their changed lives.
It depends how much we want to draw near to God. How much we seek God in prayer, read His word and ask for direction. There are thousands, even millions who will testify to God changing them. Born again.
Even if we are not drug addicts or alcoholics we are all sinners (according to the Bible) until we are born again. "For all have sinned and fall short of the glory of God." Romans 3:23. So we need salvation, which is the next topic.