A Natural History of

OurOld Friends

An account of helminthic therapy — the deliberate keeping of small, ancient companions to quiet an immune system turned against the body it was meant to defend.

Read the story
Edition I

It sounds absurd at first.

Hosting a few harmless intestinal worms — species humans lived alongside for hundreds of thousands of years — might restore something the immune system has lacked since we eliminated them.

Graham Rook, the UCL immunologist who coined the 'old friends' hypothesis, called them expected presences that the immune system evolved to accommodate — not pathogens, but companions. William Parker, the Duke biophysicist whose work underlies much of the practice, describes the result of their removal as an immune system turned evolutionarily paranoid.

Contents

Six chapters

I. The StoryHow a near-universal companion vanished — and why its absence may have made us ill. II. The OrganismsThe four organisms used therapeutically, with their habits, persistence, and temperaments. III. ConditionsThe inflammatory and autoimmune illnesses people explore this for, and where the evidence is strongest. IV. SafetyWhat's known about the risks, what the evidence shows, and what remains unsettled. V. In PracticeWhat actually doing this looks like — and how to bring a doctor in with you. VI. AccountsFirst-hand stories from people who tried it, in their own words.

Tools and references

Biological Profile Quiz

Fifteen questions about your condition, immune history, and lifestyle. Identifies where you sit on the evidence, including flags worth discussing with a clinician before you proceed.

Take the quiz

Build a Clinician Brief

A personalised, evidence-based packet to bring to your appointment, specific to your condition and history, formatted for a doctor to read quickly and take seriously.

Build the packet

Further Reading

Key researchers, foundational papers, support communities, and reference materials.

Browse resources