Background
Constipation is a common chronic bowel disorder with an incidence of more than 50% in the elderly population. Complementary and alternative medicine is a cost-effective and satisfactory treatment for constipation used widely by the elderly.

Objective
This study evaluates the efficacy of an herbal formula made from Foeniculum vulgare Mill. and Rosa damascena for the treatment of constipation in an elderly population and consequent changes to their quality of life.

Design, setting, participants and intervention
This double-blind randomized active controlled clinical trial, with parallel group allocation ratio of 1:1, was conducted in a referral clinic in Afzalipour Hospital, affiliated to Kerman University of Medical Sciences in Kerman, Southeastern Iran. Individuals over 60 years of age, diagnosed with functional constipation (based on the Rome IV criteria), were included in this study. Participants received a sachet of 10 g F. vulgare and R. damascena (herbal formula group) or polyethylene glycol 4000 (PEG 4000 group) with a glass of warm water two times a day for 4 weeks and were followed up for 4 additional weeks.

Main outcome measures
Constipation severity, stool consistency, and the quality of life were used as the primary outcomes. Drug side effects were used as a secondary outcome. The outcomes were assessed using the Constipation Assessment Scale, the Bristol Stool Form Scale, and the Patient Assessment of Constipation Quality of Life questionnaire.

Results
A total of 25 participants in each group completed the four-week treatment cycle and the eight-week follow-up. At the end of the four-week treatment cycle, all clinical outcomes had significant improvements in both groups (P < 0.05). The analysis of constipation severity (P < 0.001), stool consistency (P < 0.001), and the quality of life (P < 0.001) showed significant improvements with fewer side effects (mild diarrhea) and a longer duration of symptom relief in the herbal formula group compared to the PEG 4000 group.

Conclusion
Although both interventions significantly improved the treatment outcomes, constipation severity, stool consistency and the quality of life were improved more effectively by the herbal formula than by PEG 4000; however, the mechanism of action is not yet understood.

Trial registration
This trial was registered in the Iranian Registry of Clinical Trials (IRCTID: IRCT20200108046056N1).

Key words: Elderly, Constipation, Foeniculum vulgare Mill., Rosa damascena, Persian medicine, Randomized controlled trial