Weak Stomach (3.5e Flaw)
From D&D Wiki
You simply cannot hold food and drink down, resulting in a frail, often malnourished character.
Effect: Any time you eat or drink anything, including potions, you must succeed a fortitude save (DC 15) or be forced to vomit, losing all beneficial effects of the consumed item; you become nauseated for 1d4 rounds, even if the save is successful. Furthermore, you have a −2 penalty to all fortitude saves, as a result of your troubles.
Roleplaying Ideas: Characters with this flaw struggle to keep their food down, and appear weak and malnourished. They often have to stock large amounts of extra food in order to survive.