While consuming tryptophan can cause a rise in serotonin levels, eating a pill full of serotonin only results in your digestive system breaking it down for its amino acids...

"Serotonin taken orally does not pass into the serotonergic pathways of the central nervous system because it does not cross the blood-brain barrier. However, tryptophan and its metabolite 5-hydroxytryptophan (5-HTP), from which serotonin is synthesized, can and do cross the blood-brain barrier. These agents are available as dietary supplements and may be effective serotonergic agents. One product of serotonin breakdown is 5-Hydroxyindoleacetic acid (5 HIAA), which is excreted in the urine. Serotonin and 5 HIAA are sometimes produced in excess amounts by certain tumors or cancers, and levels of these substances may be measured in the urine to test for these tumors." - wikipedia

So you can eat tryptophan, or take SSRIs like Prozac, but eating a pill full of serotonin should have any effect on mood.