Research Update: The Effect of Garlic Tablets on the Endometriosis-Related Pains: A Randomized Placebo-Controlled Clinical Trial

Research Update articles are produced in order to keep practitioners up to date on impactful research that is relevant to the field of integrative medicine. These articles may contain summaries of recent studies, events, or other industry news that advances current knowledge and standards of care. The following article summarizes the research conducted by Amirsalari et al. titled, “The Effect of Garlic Tablets on the Endometriosis-Related Pains: A Randomized Placebo-Controlled Clinical Trial,” which was published in Evidence-Based Complementary and Alternative Medicine in 2021. (1)

Background

Endometriosis is a debilitating condition that affects approximately 10% of females of reproductive age globally. (7) It occurs when tissue similar to that lining the uterus grows outside of the uterus, leading to various symptoms including chronic pains such as dysmenorrhea (i.e., painful menstrual periods), dyspareunia (i.e., painful intercourse), and non-menstrual pelvic and back pain. The severity of symptoms is directly correlated to the severity of inflammation. (5) Given the inflammatory nature of endometriosis, herbs with anti-inflammatory effects have the potential to mitigate symptoms. The present study was the first human clinical trial that investigated the anti-inflammatory, antiproliferative, and antioxidative effects of garlic extract on endometriosis symptoms. (2)(3)(4)

Methods

The study included 120 women with surgically or laparoscopically confirmed endometriosis. To meet the inclusion criteria, participants needed to be female, aged 20 to 45, married, not diagnosed with other severe illnesses or other pelvic inflammatory conditions, literate, and a recipient of routine treatment for endometriosis. Participants were excluded if they missed two or more consequent doses of garlic tablets, were diagnosed with other diseases, or used multivitamin supplements. Participants were randomized into either an intervention or placebo group. The intervention group was provided with a 400 mg garlic tablet daily for three months, while the placebo group received identical placebo tablets. Participants were asked to rate the severity of their various forms of pain (i.e., pelvic pain, back pain, dysmenorrhea, and dyspareunia) on a four-part Visual Analogue Scale (VAS). Participants rated their pain on a scale of 0 (no pain) to 10 (the most severe pain you have ever had) before the intervention and at every monthly follow-up. The average of the four VAS scores provided indication of the overall pain. A socio-demographic questionnaire was also administered to participants to take into account other variables such as age at diagnosis, educational level, economic status, height, weight, history of infertility, alcohol consumption, and smoking habits.

Results

The overall severity of pain was significantly reduced in the intervention group, with the highest effect being on dyspareunia. The control group experienced a significant increase in the severity of pain during the three months. This study demonstrated that garlic improved pain associated with endometriosis, as the overall pain score was 73% lower in the garlic group than placebo after the intervention. ​​The authors hypothesized that there may be four ways through which garlic might relieve pain in endometriosis, including garlic’s ability to decrease oxidative stress, reduce prostaglandin production (which decreases inflammation), decrease endometrial cell proliferation, and increase estrogen elimination, as estrogen stimulates growth and sensitization of endometrial cells.

Critical analysis

The research methodology of this study had many strengths, as a randomized placebo-controlled triple-blind clinical trial was conducted. The subjects, individuals who carried out the intervention, and the statistician did not know who received which intervention. Additionally, their use of a validated tool such as the VAS to measure patient-perceived pain increased the validity of their results. (6) Furthermore, the trial was well controlled as the groups were balanced with respect to age, BMI, and age at diagnosis, indicating that these factors may not have altered results. Even though the groups included individuals with varying education levels and endometriosis stages, one-way ANCOVA tests revealed that there were still significant reductions of pain when controlling for these factors. This study has some limitations; for example, researchers obtained a convenience sample of participants recruited from the Valiasr Fertility Research Center. Convenience samples may not be representative of the population in question, as it involves recruiting people who are close by or convenient to the researcher. Since the participants were recruited from a fertility research center, it is likely that many of them experienced fertility concerns; therefore, the findings of this study may not be generalizable to all people with endometriosis, as not all women with endometriosis experience infertility. Other limitations of the study included the small sample size and short duration of the study. Since the study was limited to three months, neither the long-term effects of garlic supplementation nor the effects on pain after the discontinuation of garlic supplementation could be determined. Another limitation was that one of the exclusion criteria regarding not missing two consecutive doses was dependent on patient reports and thus may not have been entirely accurate. Furthermore, potential adverse effects were not disclosed.

The bottom line

This study provided strong evidence that garlic supplementation may improve various forms of pain experienced with endometriosis. As garlic is inexpensive, this can potentially be a feasible therapy for managing symptoms of endometriosis. Future directions of research include replicating the present study as this was the first relevant human trial, conducting larger studies, and determining the best dose of garlic extract and optimal duration of supplementation.