One thing I do sometimes is search for the name of 2 different supplements on Amazon and see if I can find a commercial stack where they appear together, then check for 1 star reviews of the stack that describe a negative interaction. (This works best for stacking supplements that have similar purposes, e.g. if you're taking 2 sleep aid supplements at once, it's plausible that they both appear in a commercial stack that someone put together.)
Similar to the Crazy Ideas Thread and Diaspora Roundup Thread, I thought I'd try making a General-Purpose Questions Thread.
The purpose is to provide a forum for asking questions to the community (appealing to the wisdom of this particular crowd) in things that don't really merit their own thread.