Subclass of Terpenoids

Iridoids

Bitter monoterpene-derived glycosides with anti-inflammatory and bile-stimulating actions.

Overview

About Iridoids

Iridoids are bitter glycosides built on a distinctive fused bicyclic monoterpene skeleton — a cyclopentane ring welded to a six-membered oxygen-containing ring. They take their name from Iridomyrmex ants, in which the parent structure was first identified.

Almost all circulate in the plant as glucosides, which keeps them stable and water-soluble. That sugar is also the trigger: break the tissue and plant enzymes cleave it, releasing a reactive aglycone that polymerizes and blackens. This is why devil's claw, gentian and valerian preparations darken with age.

Where Iridoids Occur

They mark several specific plant families and are useful chemotaxonomic markers:

Devil's claw

harpagoside and harpagide

Gentians and centaury

gentiopicroside, amarogentin, swertiamarin

Plantain, eyebright and figworts

aucubin, catalpol

Valerian

the valepotriates

Noni and madder family

asperuloside, deacetylasperulosidic acid

Olive and privet (Oleaceae)

oleuropein and the secoiridoids

Pharmacological Importance

Iridoids are the archetypal bitters. Amarogentin from gentian is one of the most bitter substances known, detectable at roughly one part in fifty million, and the reflex it triggers on the tongue — increased saliva, gastric acid and bile flow — is the entire basis of the bitter-tonic tradition.

Beyond taste, harpagoside carries devil's claw's anti-inflammatory reputation in musculoskeletal pain, aucubin and catalpol show hepatoprotective and neuroprotective activity in preclinical models, and the secoiridoid oleuropein anchors olive leaf's cardiovascular profile.

Toxicity & Safety

Intact iridoid glycosides are generally well tolerated, and the bitter herbs carrying them have long traditional records. The main practical caution is the bitter reflex itself: strong bitters increase gastric secretion and are best avoided in active peptic ulceration and hyperacidity.

The valepotriates of valerian are the group's asterisk — unstable epoxide-bearing iridoids that are cytotoxic in vitro. They degrade rapidly in dried and aqueous preparations, so ordinary valerian tea and tincture carry little of them, but concentrated fresh-plant extracts are a different matter.

Constituents

All Iridoids

37 total Filter iridoids

Open in filterable index

Source Plants

Herbs Containing Iridoids

19 herbs

Plants in the materia medica documented to carry iridoids, with the compounds each one is listed for. The bar counts how many DISTINCT iridoids are on record for a plant, relative to the best-documented — it measures breadth of record, not potency, so a plant with one well-studied compound can outrank a richer source that has simply been analysed less. Where a measured concentration is on record it is quoted inline; most entries have none yet.