Does Motrin contain aspirin

I'm not sure, but i think not b/c Motrin and aspirin are not to be taken simultaneously

one reason for this is Motrin makes aspirin less effective

No. Motrin does not contain aspirin. Motrin contains the active ingredient ibuprofen.

It is important to remember, though, that Motrin (ibuprofen) and aspirin are both in the same category of medication; they are both "NSAIDs," or non-steroidal anti-inflammatory drugs, and therefore may not be suggested to be taken at the same time.