Check out the Mushrooms & 5-HTP subthread. The consensus seems to be that there will be little, if any enhanced effect from taking 5-HTP and mushrooms together, but some also warn it could lead to gastrointestinal problems. It doesn't sound particularly dangerous, but not really useful for whatever it might add either. I'd forego the 5-HTP and just take a higher dose of mushrooms if you're looking for a stronger trip.