SHAFAQNA- Islamic Laws on fasting according to the Fatwas of the Grand Ayatollah Sistani.
Things that invalidate a fast: Deliberate vomiting
Ruling 1616: Whenever a fasting person intentionally vomits, his/her fast becomes invalid even if vomited out of necessity or because of illness or suchlike. However, if he/she vomits unintentionally or involuntarily, there is no problem [and his fast remains valid].
source: shafaqna