If you have any decent amount of Vitamin-B6 floating around 5-HTP will do more harm then good (and to think most 5htp products are sold combines with it!).
High levels of serotonin in brain = good.
High levels of serotonin in blood = possible heart valve damage.
When 5-htp is taken with Vit-b6 the conversion does not take place in the brain rather in the stomach. And from there some does get up to the brain, however most if it will be floating around in your blood and it *may* cause trouble with the heart.