Tryptophan is an essential amino acid and precursor to serotonin. In your body the tryptophan will be converted to 5-HTP (5-hydroxytryptophan) before serotonin (5-hydroxytryptamine), so 5-HTP is a step closer to serotonin anyways. I have read that tryptophan is more effective in some people as 5-HTP may cause intestinal distress. Interestingly enough tryptophan doesn't cross the blood brain barrier as well as 5-HTP does and being an essential amino acid tryptophan is used by your body for other things such as vitamin B3 synthesis.
You're not going to get any significant psychoactive effects by ingesting 5-HTP alone and high doses may carry unpleasant side effects. Ideally you would want a regimen of tryptophan, 5-HTP, niacin and melatonin to promote feelings of well-being but I doubt you could call this a 'high'. People have suggested that taking 5-HTP before smoking cannabis makes the high more euphoric and there are a few experience reports detailing this. This seems sound enough to me and I would bet that such a regimen could also enhance the effects of MDMA and hallucinogens. It seems to me your brain would roll harder and trip better if it had a sufficient supply of what it needs to function in the first place.