^ No, not at all. Let me explain a bit better.
A pro-drug needs to be metabolized by the liver before it takes effect generally. Take codeine for example; if you are deficient in the liver enzyme CYP2D6 which metabolizes it to morphine, codeine won't do much for you apart from giving you a big histamine reaction which it does pretty damn well by itself.
Heroin is also a pro-drug. It can also be referred to as 3,6-diacetylmorphine. Heroin though, is metabolized in the brain where the two major metabolites are morphine and 6-monoacetylmorphine. It is these compounds which give the euphoric and analgesic effect.
However, something like morphine doesn't need to be metabolized before it works in the brain. Put it in your blood stream either orally, nasally, anally or via IV and it crosses the BBB fairly quickly (not as fast as heroin), binds to the receptors and does it's job.
So basically, if you have a fatty liver that is in such a condition that it is affecting your metabolism and not letting it happen correctly, then certain pro-drugs may not work as they are not being metabolized into the active compound at a sufficient rate.
Though as I mentioned, in chronic alcoholics they can sometimes metabolize compounds extensively meaning a greater effect from a pro-drug though probably lasting shorter as it is metabolized quicker.
I hope that makes sense, if it doesn't let me know.
As for the blood-brain-barrier, well codeine can cross it already though not so well. It's just that codeine itself doesn't have much affinity for the opioid receptors. If you injected codeine IV for example, it would not be euphoric. In fact it would be quite dangerous, due to the massive histamine reaction it would case and could lead to a pulmonary embolism.