katebcca, I am so sorry to hear this about your son. Substance abuse is such a heart break. I recently lost my brother (he was 57) due to liver damage. He had been walking around with Hep C for years, which can lie dormant. By the time they dsicovered that his liver was in bad shape, it was too late. He started at age 16 with heroin and barbiturates. He had been on methadone for at least 35 years, which is also a drug and will damage the liver. Your son is still very young and his liver may not be that bad. A friend of mine is an alcoholic. He's 47 and has been drinking heavily, on and off, since the age of 16 and his liver seems to be be in good shape.
Keep bugging them at the prison and make sure they keep you informed. He is still your son.
I will pray for him and for you.
Peace and (((HUGS)))