The actual synthesis pathway for serotonin(5-HT) is:
Tryptophan goes to 5-Hydroxytryptophan (5-HTP) goes to Serotonin (5-HT).
There is no difference in effect between either. I also read that taking to much of either can mess up your nerves in your hands and feet IRREVERSABLY! So ask your MD about the dose you're taking.