Polymorph, HP, and Constitution damage/drain

Question

My character polymorphs into a troll and gains his new constitution score, but the HP remains the same, then his con gets damaged/drained.

What happens?

1. my Con goes down but as long as I'm a troll I don't care, HP keeps remaining the same. I lose that HP when the polymorph spell ends (and the damage/drain stays)
2. my Con goes down and so do my HP, as if my original Con score went down.
3. something else (explain)

I'm not concerned about the other effects of constitution damage/drain, since polymorph does not interfere in those.

Answer 1

When you polymorph into a troll, your hit points do not remain the same, they are adjusted for your new CON. See this Rules of the Game article.

As other CON-affecting effects apply, they also modify your CON, so yes if you get CON drained your hit points reduce.

When you change back, your base CON goes to its original but other effects (like the drain) do not go away and you now have a lower-than-your-usual CON (this can kill you if you're not careful).

Now, in a case like Alternate Form where a CON change doesn't change hit points, the RAW is unclear and also fairly problematic. It doesn't really make sense to be immune to CON drain but it also doesn't make sense to kill you fast via CON damage/drain because your non-CON-augmented hit points go down. What I would do in my game is let CON damage not affect hit points until it goes under the underlying characters' CON. So in a form with CON +8, you could get 8 points of CON damage before having to worry about it. But actually, I would probably just strike the "CON change doesn't change your hit points" rule as being pointlessly fiddly.