Assuming that 650 milligrams of ibuprofen is the recommended dose for an individual, it can be combined with 650 milligrams of acetaminophen. It is safe to combine acetaminophen and ibuprofen at their recommended doses, according to SafeMedication.
Ibuprofen and acetaminophen both work differently and have different side effects on the body, notes the Arthritis Foundation. Aspirin, naproxen and ibuprofen all work in a similar manner within the body and have very similar side effects. Unless prescribed by a health care provider, these drugs should not be taken together in order to avoid complications. A study published by the Arthritis Foundation found that the combination of acetaminophen and ibuprofen is effective in relieving pain but raised an individual's risk of gastrointestinal bleeding.