cause of indigestion is too much stomach acid. pH of NaOH is around 13, making it a strong base completely neutralising the stomach which should be around 2 - 3. As Eiervanstan said
The main point for the mark is that it would be a highly exothermic reaction, cause internal bodily damage and is therefore unsuitable. This is due to the reason that it is to strong an alkali for stomach conditions.
sodium hydroxide is a strong enough base to denaturise (break the amide and ester links) your proteins including those in your skin (throat, mouth etc)
I knew a lad who lost all of the skin off his feet because he paddled in strong NaOH solution (leaking from some pipe cleaning sacks) in the cellar of a bar while he was working there.. (months in hospital and skin grafts included)