There are really situations to be worried about with your liver: 1)acute drug induced hepatotoxicity. This is when the liver is under serious drug assault and starts to basically break down in a cascade affect resulting in fulminant liver failure. No amount of milk thistle or LIver detox or anything else is going to reverse this and this process happens rapidly enough that the liver has no chance of healing or regenerating while this is taking place. If caught early, you stop taking the offending drug and hopefully things normalize. If you are symptomatic, you go the ER. If you catch it too late, you go to the ER anyway.
The other concern is long term damage that can be asymptomatic and is cumulative. Some of this damage may be repaired while off cycle, but if significant scarring or cysts develop, then you basically start to lose liver capacity/function. You won't know this is happening unless you get regular LFT tests. If it happens over a long period of time and affects enough of your liver, then you become clinically hepatically impaired which means that your liver is less capable of detoxifying your body, which also means it is less capable of dealing with any future cycles you may do.
Do a search on Liver 101 for a post I wrote with more details. Hope this helps.