i've heard people say that if they take 5-htp too close to their roll that it will mute the effects.
This is my experience. It's a very common effect among people who have done it. I preloaded with 5-HTP for an MDMA experience because I had read that the extra serotonin provided would potentiate the trip. I always found that it made it very dull and completely killed the psychedelic, ecstatic effects.
I have 2 thoughts about why this could be; I was thinking about how I take 5-htp sometimes to help me sleep. I think that 5-htp supplements may have a fair bit of the serotonin produced from it get turned into melatonin, thus making it more dulled. It doesn't make you sleepy or tired because of the amphetamine effect of the MDMA.
I was thinking that because 5-HTP causes an increase in extracellular serotonin that occupies SERT receptors. MDMA needs to bind to the SERT receptor in order to reverse the transport pump; if the receptor is already bound by the serotonin provided by the 5-HTP, the MDMA can't bind to it; thus causing a signifigantly reduced release of serotonin from the storage vescicles.
The upside is that if you take 5-HTP before taking MDMA, you prevent such a huge release of serotonin so you don't get the serotonin depletion, or the nasty side effects associated with that.
5-HTP with psychedelics is different. There seems to be no diminished effects among people who have done it. I think it has a similar reason to why people on SSRI's can get effects from 5-HT2a agonist (traditonal) psychedelics but not from the 5-HT (serotonin) releasing MDMA.
I would venture a guess as to say that 5-HT2a agonist psychedelics are able to bind to their receptor even though there is extracellular serotonin from the 5-HTP. It's possible that the psychedelic has a higher affinity to the receptor that serotonin while MDMA has a lower affinity for the SERT than serotonin.
Now these are just my thoughts. If there's someone with information about the empirically proven effect of 5-HTP on psychedelics it'd be great to hear.
Here's a few mushrooms or LSD + 5-HTP combo threads:
http://www.bluelight.ru/vb/showthread.php?t=258959&highlight=5-htp
http://www.bluelight.ru/vb/showthread.php?t=78380&highlight=5-htp
http://www.bluelight.ru/vb/showthread.php?t=59132&highlight=5-htp
http://www.bluelight.ru/vb/showthread.php?t=58234&highlight=5-htp
and a long one and 5-HTP and visual trails:
http://www.bluelight.ru/vb/showthread.php?t=246874&highlight=5-htp