here is a link from wiki:
http://en.wikipedia.org/wiki/Grape_seed_extract
from that article:
Side effects
In clinical studies, taking grape seed extract has been associated with mild side effects such as:
- Abdominal pain
- Cough
- Headache
- Nausea
- Sore throat
As with any dietary oil, taking large amounts of grape seed oil may lead to soft stools or oily leakage from the gastrointestinal tract.