I've seen people post that one email that came back came from
John.thero@amarincorp.com
Looking at that, and the fact that there is also elisabeth.schwartz@amarincorp.com
we can assume that all emails are first.last@amarincorp.com with the caveat that the name listed (i.e. John, not Johnathon or however he spells it) is the one used.
Of note, you will get an "undeliverable" response if you guess wrong. I remember way, way back in the day, I emailed John.f.thero and it came back as "this email address doesn't exist."
Use that as you wish.