、。
I think the chances of rehabilitation are low if someone's doing habit-forming substances like thinner.
Literal
Thinner etc [genitive-の] habit-forming-ness [genitive-の] exist thing [object-を] am-doing [quotative-と] say thing [topic-は], rehabilitate possibility [subject-が] low is [quotative-と] think.
A heavy opinion delivered with several hedging layers. シンナー ('thinner,' i.e., paint thinner) refers to the solvent abused as a recreational inhalant — the topic here is substance abuse. 常習性 ('addictiveness, habit-forming property') uses the productive ~性 suffix for forming abstract '-ness/-ity' nouns. 更正 ('rehabilitation, correction of conduct') is written with 更 ('renew') + 正 ('correct') — slightly formal vocabulary from social-work contexts. The whole sentence has a three-layer nested structure: [condition] と言う事は [prediction] と思います, which uses と言う事 and と思う to embed a general claim as the speaker's opinion.