Archaeologists have uncovered the earliest known evidence of the use of the medical and psychoactive plant Peganum harmala, also referred to as Syrian rue or harmal, for fumigation around 2,700 years ago in an oasis settlement in northwestern Saudi Arabia. The study, published in Communications Biology, shows that Iron Age communities at Qurayyah intentionally burned harmal not in temples or burial practices, but in homes for therapeutic, sensory, and possibly psychoactive purposes.

One of the ancient fumigation devices used in the inhalation of harmal. Credit: Hans Sell

Led by Dr. Barbara Huber of the Max Planck Insтιтute of Geoanthropology and Professor Marta Luciani of the University of Vienna, the researchers collaborated with the Saudi Ministry of Culture’s Heritage Commission to analyze organic residues found in ancient ceramic fumigation devices. Using high-performance liquid chromatography-tandem mᴀss spectrometry (HPLC-MS/MS), they detected the characteristic alkaloids of the plant—harmine and harmane—inside the vessels.

“Our findings represent chemical evidence for the earliest known burning of harmal, not just in Arabia, but globally,” said Dr. Huber. The discovery verifies that these old Arabian communities possessed a systematic understanding of their local pharmacopeia centuries prior to the beginning of written records describing medicinal practices.

Peganum harmala possesses complex pharmacological effects. Its alkaloids are reversible MAO-A enzyme inhibitors that impact neurotransmitters such as serotonin. This can produce effects ranging from mild sedation and pain relief to hallucinations, depending on the dose. Of particular note, the mode of delivery in Qurayyah—burning seeds and inhalation of smoke—would have offered a controlled method of application, preventing toxicity through ingestion.

The oasis settlement of Qurayyah in northwestern Saudi Arabia. Credit: A. M. Abualhᴀssan

What makes this discovery even more interesting is its domestic setting. “All of the fumigation material with harmal was found inside houses, courtyards, cooking areas, and cellars,” according to the researchers.

The study also finds a specific differentiation in the use of plants in various contexts. Harmal was used within domestic contexts, whereas burial sites at neighboring oases contained aromatic substances like Commiphora and coniferous resin. This reflects a qualitative distinction within ancient Arabian communities regarding the specific roles plants played in health, purification, and spiritual life.

Harmala (Peganum harmala). Credit: Yuriy75 / CC BY-SA 3.0

Ahmed M. Abualhᴀssan, co-director of the Qurayyah project from the Saudi Heritage Commission, emphasized the cultural importance of this find: “We’re preserving not only objects, but the intangible cultural heritage of ancient knowledge that still holds relevance in local communities today.” Harmal continues to be used in traditional medicine and household fumigation in parts of Arabia.

The team suggests that ancient organic residues like these could help in the rediscovery of forgotten bioactive compounds, and therefore ultimately inform modern pharmacology. “Utilizing the information stored in ancient organic remains could enable the recovery of bioactive compounds that have been forgotten over time,” the researchers wrote.

But with modernization and globalism threatening traditional knowledge systems, researchers stress the urgency of documentation. “Such practices are increasingly disappearing,” the researchers warned. Through this study, they believe they are preserving a fine thread of ethnobotanical knowledge going back millennia.

More information: Max Planck SocietyPublication: Huber, B., Luciani, M., Abualhᴀssan, A.M. et al. (2025). Metabolic profiling reveals first evidence of fumigating drug plant Peganum harmala in Iron Age Arabia. Commun Biol 8, 720. doi:10.1038/s42003-025-08096-7