Frankincense is used in aromatherapy and religious ceremonies
A herb known as "Indian Frankincense" can reduce the symptoms of arthritis, US researchers have suggested.
Extracts from Boswellia serrata, a similar species to the variety famous for its role in the Christian nativity, were tested on dozens of patients.
Those who received it reported better movement and less pain and stiffness.
The herb has been used for thousands of years in Indian Ayurvedic medicine, reports the journal Arthritis Research and Therapy.
Osteoarthritis is the most common form of the condition, and normally affects the weight bearing joints such as hands, wrists, feet and spine.
Current treatments carry a great many adverse effects, and scientists have been hunting for an alternative.
The investigation into the properties of Boswellia serrata was led by Dr Siba Raychaudhuri at the University of California, Davis.
Eventually they tested an extract of the plant enriched with the chemical - AKBA - thought to be its active ingredient.
Some of the 70 patients with severe arthritis in their knees recruited into the trial were given a low-dose capsule, some a higher dose capsule, and the remainder were given a dummy pill with no active ingredients.
In as little as seven days, patients taking the frankincense drug reported improvements in their pain and stiffness levels compared with the placebo group, and these continued until the 90-day mark, when the study ended.
Tests of the fluid within affected joints also revealed falls in levels of enzymes linked to the condition.
Dr Raychaudhuri said: "We have shown that B. serrata enriched with AKBA can be an effective treatment for osteoarthritis of the knee."
However, UK experts urged caution. Professor Philip Conaghan, from Leeds University, and a spokesman for the Arthritis Research Campaign, said: "Certainly osteoarthritis is in need of new safe analgesics, although many effective therapies that reduce pain such as muscle strengthening exercises, shock-absorbing footwear and weight loss have very few bad side-effects.
"This report on treating knee pain with a chemical derivative of B. serrata is interesting but the patient numbers are small, there were some problems with the reported trial design and we need more information on its medium to long-term safety."