L-Tryptophan

L tryptophan is a serotonin precursor with an unusual history

Tryptophan is an essential amino acid and the precursor from which the body makes serotonin and then melatonin. This section holds 2 lines from £25 to £132.

Its history matters more than most supplements’ because of what happened in 1989.

The contamination episode

In 1989 an outbreak of eosinophilia-myalgia syndrome — a serious and sometimes fatal condition involving severe muscle pain and raised eosinophils — was traced to tryptophan supplements. Thousands were affected and dozens died.

Investigation linked the outbreak to contaminants in product from a single manufacturer following a change in production process. It was not attributed to tryptophan itself. Sales were nonetheless suspended in several countries, and the episode still shapes how the supplement is regulated and perceived.

Why that history is worth knowing

Not because tryptophan is dangerous — the evidence points to a manufacturing contaminant rather than the amino acid. It is the clearest documented case of a supplement causing mass harm through production quality rather than through its active ingredient, which is a lesson about who makes what you buy.

What it does

Supplementation raises tryptophan availability, which can raise serotonin synthesis. Evidence for sleep and mood is modest and inconsistent — well short of a treatment.

One practical complication: tryptophan competes with other large amino acids for transport into the brain, so a protein meal reduces how much gets through. Timing matters more here than with most supplements.

Against 5-HTP

5-HTP is one step further along the same pathway and does not face the same transport competition, which is why it is often preferred. Neither should be combined with SSRIs or other serotonergic drugs — that combination risks serotonin syndrome, and it is a genuine hazard rather than a theoretical one.

Where it sits in this catalogue

It is one of the few things stocked here aimed at mood and sleep rather than training outcomes. DSIP and the supplements range sit either side of it.

Quality, given the history

The 1989 episode makes supplier provenance more pointed here than almost anywhere on this site. The checks in how to check a brand is genuine apply with unusual force.

Frequently asked questions

Is tryptophan safe?
The 1989 outbreak was traced to contaminants from one manufacturer, not to the amino acid itself.

What was EMS?
Eosinophilia-myalgia syndrome — a serious condition affecting thousands and causing dozens of deaths in 1989.

Does it help sleep?
Evidence is modest and inconsistent. It is not a treatment for insomnia.

Should it be taken with food?
Protein reduces its uptake into the brain, since it competes with other amino acids for transport.

Can it be taken with an antidepressant?
No. Combining serotonergic agents risks serotonin syndrome.