The red forest provides poisons which, in proper dosage, are medicinally useful, and there is barely a sickness for which a cure cannot be found in there; but it's difficult to travel, and many cures still await their discovery.
"I was astonished when they brought me a redforester - a sick redforester? I couldn't find what was wrong with her until a desperate attempt, following a seemingly outlandish theory, revealed the cure to be tsemakar venom and the matching antidote. Apparently, redforesters need to be poisoned daily to be well."Elves are proverbially "more different than others", and display a range of differing reactions to normal medicine. But in the end, every species has its preferences; garren show better healing when the medicine is applied hot, raganaj when it's based on animals, both as well as dwarves show in their colouring when they're not well.
— Jraneh, apothecary
Most sicknesses affect all species, if not always with the same symptoms; bluefinger disease, for example, does the same to everyone, while only shankeh can get straipiness, and only humans suffer from the cold (which is a source of amusement to other species - stand them in cold water, they get sick. Hilarious.).
"My shankeh patients would have needed rest to heal properly, but their need to run always drove them out of bed and their condition worsened. So I finally, if arguably, turned to the practice of either putting a nail into the knee, or breaking the leg altogether."
— Vranejar, Gamahanian doctor
There's always this chance when building a world that you either make it a hellhole where everything's dangerous and rotten, or way too nice because every problem has been solved, so I design diseases and poisons carefully (and civil wars, insanity, and tyrannies). The red forest may well treat everything there is from cancer to the common cold, but finding anything is bloody difficult. Literally.
It's fun to come up how elves react differently to things, and define the miniscule differences between species' physiology, seen from a medic's perspective. There are of course lists of these, but I won't bore you with them.