This site is one big hatchet job. The arguments made are weak or nonexistant when the papers that are cited to support them are actually examined. And the website makes it annoying to actually find the titles of the papers it cites.
For example the "high dose tryptophan causes liver damage" claims are false, the liver damage in previous studies was due to other factors:
Rat liver is not damaged by high dose tryptophan treatment.
Another example: I quote the website on its chapter "Tryptophan Side Effects: The Promotion Of Cardiovascular Events"
Note how "cardiovascular events" suggest heart infarcts and the like.
Serotonin, which is increased by L tryptophan loading (Mateos, et al., 2009), is clearly implicated in cardiovascular disease and other tryptophan side effects (Gaddum & Hameed, 1954; Koren-Schwartzer, et al., 1994; Mohammad-Zadeh, et al., 2008; Peat, Summer 2009; Maclean & Dempsie, 2009 & 2010).
1.
Mateos, et al showed a ~25% increase (guesstimation on my part, but it's roughly there) in plasma serotonin in rats fed 125 mg/kg tryptophan. For a human of 70kg that's 8.75g of tryptophan.
2.
Gaddum & Hameed: this is a study from the 50's on serotonin blocking drugs. I don't see how this paper is related to the arguments made. Maybe he believes intestinal motility to be a "side effect" of serotonin?
3.
Koren-Schwartzer, et al: They injected serotonin into rats at dosages that induced brain damage so they could study the protective effect of certain drugs.
4.
Mohammad-Zadeh, et al: This is a review of literature on serotonin. It describes serotonine syndrome, which is the result of combining multiple agents that increase serotonin (usually an antidepressant plus tryptophan or 5-HTP).
5. Peat, Summer 2009: This is not a paper and I cannot find its source. I note that Peat is prominently featured throughout the website.
6. Maclean & Dempsie, 2009 & 2010: Two papers [
1][
2] on serotonin involvement in pulmonary hypertension. This is a legitimate concern. Serotonin acts as vasoconstrictor specifically in pulmonary arteries, so serotonin agonists will increase the risk or severity of pulmonary hypertension. The argument is stupid though, it should be common sense to not take vasoconstrictors with a problem of hypertension, just as one wouldn't take vasodilators with a problem of hypotension.
As you can see, the entire paragraph and argumentation falls apart when the papers that are cited are actually examined. The website uses weasel words to suggest that serotonin is harmful in vague terms. The papers refer mostly to the "
other tryptophan side effects" part, and not the primary claim. There isn't even a shred of evidence that normal usage of tryptophan or 5-HTP will cause any problems.
Of course, I haven't looked at everything but it seems pretty clear that this website is deliberately trying to scare readers and doesn't care at all about factual criticisms.
Other times papers are simply misunderstood (like with the "serotonin causes heart damage" claim). It's not uncommon to overdose serotonin in animal studies for various purposes (for example for the study of serotonin-secreting carcinoid tumors), but that doesn't mean any of the observed negative effects are a real risk when taking sane doses of tryptophan or 5-HTP (because they actally don't increase blood serotonin much). To illustrate how wrong this logic is: everybody knows that you should drink 2 liters of a water per day, but if you drink 20 liters you'll get water intoxication and perhaps even die.