Serotonin and constipation are more connected than most people realise. You’ve probably heard serotonin called “the happy chemical.” But over 90% of the serotonin in your body isn’t made in your brain at all — it’s made in your gut, and it does a completely different job there.

In this episode, I break down what gut serotonin actually does for motility, why gut and brain serotonin are largely separate systems (even though your gut and brain are still deeply connected, just through other pathways), what can cause reduced gut serotonin production, and what the newest research says about the gut bacteria that may influence it. If constipation has been part of your picture despite addressing diet, hydration, and structural factors, this episode adds a genuinely underexplored piece to the puzzle.

What This Serotonin and Constipation Episode Covers

✔ Why over 90% of your body’s serotonin is made in your gut, not your brain

✔ You’re curious about the link between serotonin and constipation, and want the actual mechanism explained accurately

✔ Why gut and brain serotonin are made by different enzymes, and don’t directly affect each other the way you might think
✔ The receptors behind gut motility — and why some anti-nausea medications cause constipation as a side effect

✔ What causes reduced gut serotonin production, including the role of dysbiosis and antibiotics

✔ The newest research on gut bacteria that may boost serotonin production and support gut nerve health

✔ The evidence-backed link between fibre, short-chain fatty acids, and serotonin production

✔ Why I’m cautious about specific probiotic strain claims for serotonin, and what the evidence actually supports

Who This Episode Is For

• You’ve addressed diet, hydration, and structural factors, and constipation is still an issue
• You’re curious about the gut-brain connection, but want the actual mechanism explained accurately
• You want to understand why some medications (like anti-nausea drugs) can cause constipation
• You’re interested in the emerging research on gut bacteria and motility, with an honest read on what’s proven versus early-stage
• You want another genuinely evidence-based reason fibre matters, beyond bulk and bacteria

Listen to the Full Episode

This episode explains the actual mechanisms behind gut serotonin and motility, what causes it to become depleted, and what the evidence really supports — no overclaiming, no hype.

• ▶️ YouTube
• 🎙 Apple Podcasts
• 🎙 Spotify

Research referenced in this episode:

1. Mawe GM, Hoffman JM. Serotonin signalling in the gut—functions, dysfunctions and therapeutic targets. Nature Reviews Gastroenterology & Hepatology. 2013;10(8):473-486.
2. Gershon MD, Tack J. The serotonin signaling system: from basic understanding to drug development for functional GI disorders. Gastroenterology. 2007;132(1):397-414.
3. El-Merahbi R, Löffler M, Mayer A, Sumara G. The roles of peripheral serotonin in metabolic homeostasis. FEBS Letters. 2015;589(15):1728-1734.
4. Terry N, Margolis KG. Serotonergic mechanisms regulating the GI tract: experimental evidence and therapeutic relevance. Handbook of Experimental Pharmacology. 2017;239:319-342.
5. Enteric Microbiota-Mediated Serotonergic Signaling in Pathogenesis of Irritable Bowel Syndrome. International Journal of Molecular Sciences. 2021;22(19):10235.
6. Yang W, Cong Y. Antibiotics-induced depletion of mice microbiota induces changes in host serotonin biosynthesis and intestinal motility. Journal of Translational Medicine. 2017;15:34.
7. Yano JM, Yu K, Donaldson GP, et al. Indigenous Bacteria from the Gut Microbiota Regulate Host Serotonin Biosynthesis. Cell. 2015;161(2):264-276.
8. Reigstad CS, Salmonson CE, Rainey JF, et al. Gut microbes promote colonic serotonin production through an effect of short-chain fatty acids on enterochromaffin cells. FASEB Journal. 2015;29(4):1395-1403.

Connect with gut health naturopath Lynda Griparic: Instagram

As a naturopath with extensive experience in complex gut health conditions, I offer telehealth consultations across Australia and internationally. If you’ve addressed the obvious factors and constipation is still an issue, self-prescribing can only take you so far. I would love to help you work out why. This is exactly the kind of work I do.

[Book a telehealth consultation]

If you have a gut health question you’d like answered or would like to discuss your situation, email info@lyndagriparic.com or leave a comment below.

This content is for educational purposes only and is not intended as medical advice. Please consult your healthcare provider before making any changes to your diet or health routine.