How Serotonin Turns Into Melatonin

TL;DR

  • Serotonin converts to melatonin in the pineal gland, triggered by darkness
  • This conversion is why supporting serotonin also supports your sleep cycle
  • 5-HTP → serotonin → melatonin is the complete pathway that 5-HTP supports
  • Low serotonin means less raw material for melatonin production
  • This is why 5-HTP can support both mood and sleep through a single pathway

Introduction

One of the most useful things to understand about sleep chemistry is that serotonin and melatonin aren't separate systems — they're the same system, in sequence. Serotonin comes first, melatonin follows. This is why what you do to support serotonin during the day affects how well you sleep at night.

What This Means

Melatonin doesn't appear from nowhere. Your body makes it from serotonin — specifically, in a small gland in the centre of the brain called the pineal gland. As the sun sets and light levels drop, the pineal gland converts stored serotonin into melatonin, which then signals to your body that it's time to sleep.

If serotonin levels are low — due to stress, poor diet, low sunlight exposure, or other factors — there's less raw material available for melatonin production. The result is often difficulty falling asleep, lighter sleep, or waking in the night.

How It Works

The conversion happens in two steps inside the pineal gland:

Step 1: Serotonin is converted to N-acetylserotonin by an enzyme called AANAT. This enzyme is activated by darkness — it's essentially your body's internal sunset detector.

Step 2: N-acetylserotonin is converted to melatonin by another enzyme called HIOMT. The melatonin is then released into the bloodstream, dropping your body temperature and signalling sleep.

The full chain: Tryptophan → 5-HTP → Serotonin → Melatonin

Key Points

  • Darkness triggers conversion: The serotonin-to-melatonin conversion is activated by darkness — this is why light exposure in the evening suppresses melatonin
  • Serotonin is the raw material: No serotonin, no melatonin — the most direct link between mood chemistry and sleep
  • 5-HTP supports the whole chain: By supporting serotonin production, 5-HTP supports melatonin production naturally
  • Timing matters: Evening use of 5-HTP aligns with the body's natural conversion window — see When Should You Take 5-HTP?
  • Screen light disrupts it: Blue light from screens inhibits AANAT — the enzyme that starts the conversion — which is why screens before bed delay sleep

Who This Is For

  • Anyone who wants to understand why 5-HTP supports sleep as well as mood
  • People who've tried melatonin supplements and want to understand the upstream alternative
  • Those curious about the biology behind their sleep problems

FAQs

If serotonin converts to melatonin, why take 5-HTP instead of melatonin?

Melatonin supplements give you the end product directly. 5-HTP supports the production of melatonin naturally, working with your body's own rhythm rather than bypassing it. See 5-HTP vs Melatonin for Sleep for a full comparison.

Why does screen light suppress melatonin?

Blue light from screens inhibits the AANAT enzyme that starts the serotonin-to-melatonin conversion. Reducing screens in the evening allows the conversion to happen at the right time. See Why Screens Affect Your Sleep Cycle for more.

Can you have good serotonin but low melatonin?

Yes — other factors affect melatonin production, including age (melatonin production declines with age), light exposure, and pineal gland function. But serotonin availability is a key upstream factor.

Does this mean taking 5-HTP in the morning wastes the melatonin benefit?

Not entirely — serotonin produced during the day can be stored and converted to melatonin in the evening. But evening timing aligns better with the conversion window.

Does supporting serotonin always improve sleep?

For people whose poor sleep is linked to low serotonin or mood, yes — often significantly. For people whose sleep issues have other root causes, the effect may be smaller.

Summary

Melatonin is made from serotonin — it's not a separate system. When serotonin is well-supported, melatonin production follows naturally. 5-HTP supports this entire chain by providing the building block your body uses to make serotonin, which then becomes the melatonin that drives your sleep cycle.

Considering 5-HTP?

Equil's 5-HTP is sourced from Griffonia simplicifolia, third-party tested, and free from unnecessary fillers. Visit our 5-HTP product page or read the Complete Guide to 5-HTP to learn more.