Simply drink 50 health potions
You'll need to progress through the storyline until you unlock the ability to gain tech points, and speak to Clotho in the swamp to the west of the graveyard to unlock the alchemy tree.
Health potions are one of the simplest recipes, it requires health solution and life powder.
Carrots give 3 health solutions and intestines give 2 life powder. There are other items that give the ingredients but they are much harder to find (e.g. sulfur for life powder)
I recommend crafting 50, saving, drinking them all and then reloading. You get to keep the potions that way and also net the achievement.