I sometimes hear people who struggle with drug or alcohol addiction say things like “once an alcoholic, always an alcoholic,” or “once an addict, always an addict.” I suspect it’s part of their AA or NA rehab counseling.
It may be true that this person will always be tempted in those areas, but the Bible never treats alcohol or drugs as a “disease,” nor does it say this condition is incurable. In fact, the doctrine of sanctification gives great hope, because it teaches than any born again believer becomes dead to sin and can gain victory over whatever deeply rooted problems and behavior exist in their lives (drugs, alcohol, sex, anger, etc.).
The Christian is never bound and gagged to the power of sin.
Romans 6:11-14 Even so consider yourselves to be dead to sin, but alive to God in Christ Jesus. Therefore do not let sin reign in your mortal body so that you obey its lusts, and do not go on presenting the members of your body to sin as instruments of unrighteousness; but present yourselves to God as those alive from the dead, and your members as instruments of righteousness to God. For sin shall not be master over you, for you are not under law but under grace.
Concerning this passage, Wayne Grudem explains,
To be dead to the ruling power of sin means that we as Christians, by virtue of the power of the Holy Spirit and the resurrection life of Christ working within us, have power to overcome the temptations and enticements of sin. Sin will no longer be our master, as once it was before we became Christians.
In practical terms, this means that we must affirm two things to be true. On the one hand, we will never be able to say, “I am completely free from sin,” because our sanctification will never be completed (see below). But on the other hand, a Christian should never say (for example), “This sin has defeated me. I give up. I have had a bad temper for thirty-seven years, and I will have one until the day I die, and people are just going to have to put up with me the way I am!” To say this is to say that sin has gained dominion. It is to allow sin to reign in our bodies. It is to admit defeat. It is to deny the truth of Scripture, which tells us, “You also must consider yourselves dead to sin and alive to God in Christ Jesus” (Rom. 6:11). It is to deny the truth of Scripture that tells us that “sin will have no dominion over you” (Rom. 6:14).
This initial break with sin, then, involves a reorientation of our desires so that we no longer have a dominant love for sin in our lives. Paul knows that his readers were formerly slaves to sin (as all unbelievers are), but he says that they are enslaved no longer. “You who were once slaves of sin have become obedient from the heart to the standard of teaching to which you were committed, and, having been set free from sin, have become slaves of righteousness” (Rom. 6:17–18). This change of one’s primary love and primary desires occurs at the beginning of sanctification. (Systematic Theology, p. 747)