The herbal supplement has previously been shown to help with lower urinary tract symptoms caused by benign prostatic hyperplasia (BPH), a non-cancerous swelling of the prostate thought to affect more than half of all men over 50.
In the new research, published on 1 June in the online issue of the World Journal of Urology (DOI: 10.1007/s00345-005-0501-9), 129 men who took the supplement for 24 weeks had a substantially higher reduction in symptoms than a placebo, said the researchers from the Institute of Urology in Moscow.
The product, called Prostagutt forte (also known as PRO 160/120) in Germany, is manufactured by the German firm Willmar Schwabe. It is sold in the US as both ProstActive Plus and Prostol by Nature's Way.
Each capsule contains 160mg of WS 1473, an extract of saw palmetto berry, and 120mg of WS 1031, an extract of nettle root.
In the unconventional design, all men in both groups received the placebo on a single-blind basis (the researchers knew that all men were receiving a placebo, but the men did not), followed by a 24-week double-blind period in which the patients received 2 capsules per day of the herb combination or the placebo.
This double-blind period was then followed by a 24-week open-control period during which all patients were administered PRO 160/120. The trial design also included an optional 48-week follow-up period after the control period, creating a total observation period of 96 weeks.
To determine the treatment efficacy of the herbal combination, researchers recorded patient assessment of LUTS by using the International Prostate Symptom Score (I-PSS) test, a self-rating questionnaire, as well as a quality of life index.
Measures for efficacy include the maximum urinary flow rate, average urinary flow rate, urinary output, duration of urination and flow increase (all determined by means of an electronic uroflow recorder), residual urinary volume and size of prostate (both determined by ultrasound) as well as uroflow and sonographic parameters.
Patients treated with PRO 160/120 exhibited a substantially higher total score reduction after 24 weeks of treatment with a tendency in the same direction after 16 weeks. This applied to men who experienced symptoms of urinary obstruction as well as to irritation and to patients who exhibited moderate or severe symptoms of BPH at the outset of the trial.
Patients in the placebo group showed a marked improvement in LUTS after being switched to PRO 160/120 during the open control period.
The trial also demonstrates a high degree of safety for the herb combination. The incidence of adverse effects for the men in the herb group was the same as those in taking the placebo. The tolerability of PRO 160/120 was comparable to the placebo.
"The clinical literature confirming the efficacy of saw palmetto is extensive and the evidence for nettle root's benefits keep growing," said Mark Blumenthal, founder and executive director of the American Botanical Council, an independent herbal education organisation.
"Although the safety and efficacy of an herb or herbal product cannot be determined by the results of only one clinical trial, in the case of the saw palmetto and nettle root preparation, the combination of the literature on each ingredient, plus the new trials on the combined formulation, demonstrate that this phytomedicinal product is both safe and effective for treating many symptoms of BPH."
Saw palmetto is widely used in preparations for treating symptoms of BPH. Research on nettle root shows that, like saw palmetto, it too inhibits the enzyme involved with the conversion of testosterone to dihydrotestosterone, a principal mechanism in the development of BPH.
Both saw palmetto and stinging nettle root are approved by the Commission E of the German Federal Institute for Drugs and Medical Devices as nonprescriptions medications to treat symptoms of BPH.