A systematic review and meta-analysis published in Frontiers in Pharmacology has uncovered a notable placebo response in patients with irritable bowel syndrome (IBS) participating in clinical trials involving herbal medicine. The study, which analyzed data from 24 randomized controlled trials (RCTs) encompassing 2596 patients, found that 37% of IBS patients receiving herbal placebos reported a positive response (P < 0.01, I² = 75%).
The research team, led by investigators from Xiyuan Hospital, China Academy of Chinese Medical Sciences, aimed to evaluate the herbal placebo response in RCTs focused on herbal medicine for IBS. The analysis included trials published between January 1994 and November 2023, sourced from databases such as PubMed, EMBASE, the Cochrane Library, CNKI, Wan Fang, and Sinomed.
Impact on Abdominal Pain and Stool Improvement
Beyond the overall response rate, the study also assessed the impact of herbal placebos on specific IBS symptoms. Among patients receiving herbal placebos, 29% experienced an improvement in abdominal pain (P = 0.83, I² = 0%), while 46% reported improvements in stool consistency and frequency (P < 0.05, I² = 71%).
Sources of Heterogeneity
The researchers identified significant heterogeneity in the placebo response, with research location and treatment duration emerging as key factors. This suggests that variations in study design, patient populations, and cultural contexts may influence the perceived effectiveness of placebos in IBS trials.
Implications for Herbal Medicine Research
Interestingly, the study found that adding a low dose of herbal ingredients to the placebo did not significantly enhance the therapeutic effect. This finding challenges the notion that the mere presence of herbal components in a placebo could artificially inflate the observed treatment response. The authors emphasize the need for uniformity and standardization in the preparation and evaluation of herbal placebos to ensure the integrity of clinical trial data.
"There is a significant herbal placebo response in patients with IBS," the authors concluded. "Different research locations and treatment durations are major sources of heterogeneity that may affect IBS patient response rates."
