Objective To evaluate the effectiveness and safety of Maziren Pill（麻子仁丸） for preventing constipation after unilateral total hip arthroplasty. Methods Eighty patients undergoing unilateral total hip arthroplasty were randomly divided into treatment group and control group

with 40 patients in each group. Preoperative education and knowledge on prevention of constipation was provided to patients in both groups during perioperative period. Additionally

Maziren Pill was administered in treatment group

6 g each time

one time on the day of surgery

and twice daily for three days after surgery. Outcomes included constipation during hospitalization; use of soap suds enema to stimulate defecation; first spontaneous bowl movement within two days after surgery; constipation and re-hospitalization 30 days after surgery; and adverse events. Multivariate logistic regression was used to calculate the risk and protective factors of postoperative constipation during hospitalization. Results Constipation occurred during hospitalization in 11 patients of treatment group while in 24 patients of control group

and the difference between groups were statistically significant（P=0.003）. Seven patients in treatment group and 16 patients in control group needed soap suds enema to help stimulate defecation（P=0.026）. Twenty-two patients in treatment group

12 patients in control group had spontaneous bowl movement within two days after surgery（P=0.024）. There were no statistically significant differences between groups in postoperative constipation and re-hospitalization 30 days after surgery（P>0.05）. There were two cases of mild diarrhea

two cases of abdominal pain

11 cases of nausea

and six cases of vomiting in the treatment group

while eight cases of abdominal pain

14 cases of nausea

and eight cases of vomiting in the control group; there was no significant difference in adverse events between groups（P>0.05）. Logistic regression analyses showed that oral Maziren Pill was a protective factor for postoperative constipation（OR=0.149

P=0.003）

and postoperative intramuscular injection of tramadol was a risk factor（OR=3.037

P=0.005）. Conclusion Oral Maziren Pill can effectively reduce postoperative constipation in patients undergoing unilateral total hip arthroplasty

promote early bowl movement

and reduce remedies to stimulate defecation

without increasing risk of postoperative gastrointestinal adverse events.