As long as you don't buy on Amazon, Cycle Assist has NAC already in it. Since Amazon is not allowing NAC products anymore, there has to be a special non-NAC containing formula of Cycle Assist for Amazon.
TUDCA is a great ingredient and can be added if you'd like to. The actual need for it depends on the harshness of the cycle, but many of us use TUDCA on any cycle just as a precautionary measure.
CEL has a TUDCA product and was one of the first, if not the first company to offer one.
Important note on TUDCA - this is one of the most problematic raw materials out there as far as quality. If the price seems too good to be true, it probably is. I've seen brands pop up especially on Amazon claiming to sell it for prices that are less than it even costs to make it. I even had a retailer last week show me where a 'contract manufacturer' claimed they could sell them 144 units for less than it costs for the raw materials. I put 'contract manufacturer' in quotation marks there bc I have no respect for any contract manufacturer that doesn't test their raws, especially on one that is known to not always be what its supposed to be which is because the raws are so expensive.
CEL tests every batch of raw materials, even if they are from the same supplier over and over again. This is one of those raws that everyone else should do the same but unfortunately many don't because its already so expensive so it makes it even less margin when you have to cost average testing fees into it.