5-HTP

5-HTP (also called oxitriptan) is a naturally occurring amino acid and the direct precursor to serotonin (5-HT). Your body makes 5-HTP from the dietary amino acid tryptophan using an enzyme called tryptophan hydroxylase. Another enzyme, aromatic L-amino acid decarboxylase (AADC), quickly converts 5-HTP into serotonin. Because of this, 5-HTP in blood or urine is usually low and short-lived.

Why It Matters

Serotonin helps regulate mood, sleep, appetite, gut movement, pain perception, and even platelet activity. Measuring 5-HTP (along with metabolites like 5-HIAA, the main serotonin breakdown product) gives insight into:

• Serotonin pathway activity

• Effects of supplements

• How your body processes serotonin outside the brain

Importantly, 5-HTP is often sold over-the-counter as a supplement for mood, appetite, and sleep. This means test results can be strongly influenced by recent use.

Biochemistry in Brief

Tryptophan → (tryptophan hydroxylase) → 5-HTP → (AADC) → Serotonin (5-HT) → 5-HIAA (urinary metabolite)

After taking 5-HTP by mouth, labs often see higher urinary 5-HIAA. This shows that 5-HTP is converted to serotonin in the body (outside the brain) and then broken down.

How the Test is Reported

• Some labs use urine, others blood.

• Related markers (like serotonin or 5-HIAA) may also be included.

• First-morning urine, normalized to creatinine, is best for consistent comparisons.

Interpreting Results

In-range / typical

• Reflects usual diet and normal 5-HTP metabolism.

• If you feel well, no special action is usually needed.

Elevated

• Most often due to recent 5-HTP or tryptophan supplements.

• May also occur with:

  • Non–first-morning urine samples

  • Very protein-rich meals

  • Hydration or collection factors

• Often paired with higher urinary 5-HIAA.

What to do:

• If safe, consider stopping supplements for 3–5 days and repeat a morning, creatinine-normalized test.

• Talk to your doctor about any medications or other supplements that affect serotonin.

Low

• May simply mean that 5-HTP was quickly converted into serotonin, which is normal.

• Can also reflect low protein intake or fasting.

• Should always be interpreted together with serotonin, 5-HIAA, and your symptoms.

Important Context & Cautions

• Brain vs. body: A blood or urine 5-HTP level does not directly show brain serotonin. The brain tightly controls neurotransmitter levels.

• Drug/supplement interactions: 5-HTP can combine with SSRIs, SNRIs, MAO inhibitors, tricyclics, buspirone, triptans, St. John’s wort, and other serotonergic agents. Taking these together can increase the risk of serotonin toxicity.

• Digestive effects: Because much serotonin is made in the gut, high peripheral conversion of 5-HTP may cause nausea or GI symptoms.

• Collection factors: Hydration, meals, timing of the sample, and supplement use within 72 hours all influence results.

Tips for a Clearer Test Result

• Use a first-morning urine sample (if urine test).

• Check that results are creatinine-normalized.

• Record a 3–5 day diary of your diet, supplement doses/timing, caffeine, alcohol, sleep, and exercise.

• If results are unclear or unexpectedly high, repeat after a safe supplement washout (3–5 days).

When to Follow Up

• Persistently high results without supplements

• Elevated values with symptoms such as headaches, flushing, GI upset, agitation, or sleep changes

• Any suspected supplement–medication interaction

Speak with your doctor for guidance, especially if you use prescription medications that affect serotonin.

Bottom Line

5-HTP is the direct precursor to serotonin and is usually kept low in the body. Test results are strongly influenced by supplement use. Elevated values most often reflect recent intake of 5-HTP or tryptophan and may show up alongside higher urinary 5-HIAA. Always use consistent sample collection, interpret results together with related markers and your symptoms, and discuss any changes in supplements or medications with your healthcare provider.