Why are some doctors saying to avoid ibuprofen or only use at most 400mg once a week? others seem to prefer in general.

A few reasons:: Ibuprofen (advil, motrin), like other anti-inflammatories, has the potential to cause increased stomach acid and therefore contribute to the risk of ulcers and intestinal bleeding. That's the main reason why everybody is up in arms about motrin. It is excreted through the kidneys, so there may be concerns with kidneys or blood pressure. If you have never had a problem, great. If so, use with care.