Complex sentence: According to some clinicians and researchers, a drug addict is someone for whom sobriety is a tenuous and temporary state, who almost always resume drug use, even if they have been free of drugs for years.
Split into simpler sentences: According to some clinicians and researchers, a drug addict is someone for whom sobriety is a tenuous and temporary state. Drug addicts almost always resume drug use, even if they have been free of drugs for years.