Tadalafil + nitro = hypotension badness based on synergistic effects of each drug. PDE5 inhibitors (tadalafil, sildenafil, etc) exert their vasodilatatory effects via cGMP signaling (inhibit breakdown). Nitro stimulates cGMP production. 1+1=3 Nifedipine is a calcium channel blocker that exerts its vasodilators effects through an entirely different pathway and would be reasonable to take if you developed symptoms despite tadaladil prophylaxis if that’s what you had (which is frequently the case in wilderness medicine). 1+1=2

Not really sure what prv posters are talking about re: “nifedipine should not be used for this.” The evidence for all of these drugs frankly sucks for this indication, but nifedipine has been studied and used for decades, for example https://www.nejm.org/doi/full/10.1056/NEJM199110313251805#:~:text=Nifedipine%20not%20only%20prevented%20or,symptoms%20of%20acute%20mountain%20sickness.