Re: Kidney and Partial Liver Transplant Recipient, Parasite Cleanse, Liver Flush?

If I were him, I would proceed with an abundance of caution. Unless he got the organs from an identical twin (which I'm assuming isn't the case, just by the odds!), there's the possibility of alloreactivity, so he must be on immunosuppressive drugs. If these immunosuppressants are not kept at proper levels, he will either reject the organ (and become very sick) or possibly become too immunosuppressed (which can also make him very sick because he'll be prone to infections). The danger of herbs and other alternative remedies is that they can change the levels of immunosuppressive drugs in his system.
Many herbs and other natural remedies ARE drugs, in the sense that they have to be metabolized and cleared by the body. Herbs (and other drugs) can alter the metabolism of other drugs in many ways: there are multiple mechanisms by which this occurs (ask if you're interested) but some of the things they can do include making the liver metabolize other medications too quickly (so you don't have enough of them) or making them metabolize the drug too slowly (so you have too much). When it comes to immunosuppressant drugs in a transplant recipient, the consequences of this can fatal.
Also, many flushes contain laxatives (natural or otherwise) which decrease intestinal absorption - i.e. they may make it so that he cannot absorb the medications that he needs.
Even certain foods can alter the level of medications in your system (for example, grapefruit is famous for inhibiting the enzyme CYP450, which is responsible for the metabolism of many common drugs. People who eat grapefruit or drink the juice while on these drugs will have much higher levels of the drug than they should) - just because it's natural does not mean it is safe!
I would advise him to bring a list of the ingredients in any remedy he plans on using to his doctor, so his doctor can tell him whether they will interact with his current medications. Don't be too surprised, though, if the best answer the doctor can give is "we don't know, but better safe than sorry". There are a ton of natural remedies out there - the only way a doctor knows that one of them can cause a fatal interaction is when it actually does.
For many conditions and/or medications, an alteration of the level of drugs in your system is not likely to have serious consequences. However, for transplant recipients, this is not the case! It CAN be fatal.