Iriweriya (Plectranthus zeylanicus): The Fragrant Ceylon Herb Science Rediscovered

Iriweriya (Plectranthus zeylanicus) carries Ceylon in its scientific name and its scent in every Sri Lankan fever remedy: a small, soft-leaved herb of the mint family whose aroma fills a house when it is boiled. Village practitioners keep it for fevers, coughs and wounds, and physicians add it to the classic peyawa decoction. It received little scientific attention until 2022, when a study in Pharmaceuticals declared it "a rich source of secondary metabolites" and confirmed much of what the villages already knew.

Botanical and Cultural Background

A low, spreading aromatic herb with succulent stems and rounded, scalloped, softly hairy leaves, iriweriya is native to Sri Lanka and southern India and is grown in home gardens and temple grounds across the wet zone. It propagates easily from cuttings and is often planted at the edge of paths, where brushing past releases the fragrance. It should not be confused with kapparawalliya (Plectranthus amboinicus), a larger, thicker-leaved relative with different uses.

Traditional Uses in Sri Lankan Medicine

• Fevers and colds — leaf decoction, and as an ingredient of peyawa fever drinks with coriander and ginger.
• Coughs and chest congestion — leaf juice with bee honey; steam inhalation of the boiled leaves.
• Wounds, boils and skin infections — crushed leaves or leaf paste applied externally.
• Urinary complaints — decoction as a mild diuretic and for burning urination.

What the Research Shows

The 2022 Pharmaceuticals study characterised the plant's essential oil and extracts, identifying abundant terpenoids and phenolic compounds, and demonstrated notable antimicrobial activity against bacteria and fungi, disinfectant potential and anti-inflammatory effects in laboratory assays — findings that align with the wound and infection uses. Earlier Sri Lankan work had reported antioxidant and antibacterial activity. The plant is otherwise under-researched: no animal studies of its fever-reducing effect and no human trials have been published, so its long tradition, rather than clinical data, remains the main basis for use. It is also considered worth studying as a natural preservative and disinfectant.

Evidence updated September 2026.

How Iriweriya Is Prepared

For fever, a handful of fresh leaves is boiled in three cups of water for ten minutes, strained and taken warm, often combined with coriander seed and a slice of ginger as peyawa. For coughs, a teaspoon of fresh leaf juice is mixed with bee honey. For skin, wash and crush a few leaves and bind over the boil or wound, changing twice daily. The plant grows readily from a stem cutting in a pot.

Safety and Precautions

Iriweriya has a long record of safe traditional use, but formal safety studies are lacking; use in traditional amounts for short periods. Avoid concentrated preparations in pregnancy and for infants for lack of data. Skin applications can occasionally irritate; test a small area first. Persistent high fever needs medical assessment — dengue and other infections must not be treated with herbs alone.