A drug originally developed to treat tapeworm infections could offer new hope for women suffering from endometriosis, a chronic and often painful condition affecting around 1.5 million women in the UK. Niclosamide, a medication in use for nearly 60 years to kill gut parasites by blocking their glucose uptake, has been modified by researchers to target endometriosis lesions with promising results in animal models.

Endometriosis occurs when tissue similar to the lining of the womb grows outside the uterus, often on the ovaries, bowel, bladder, or even more rarely in the spine, lungs, or brain. This displaced tissue responds to menstrual cycles, causing inflammation, pain, scarring, and the formation of fibrous bands called adhesions, which can cause organs to stick together. It is also a common cause of female infertility. Despite its prevalence, women frequently face long delays in diagnosis—averaging over nine years, according to Endometriosis UK.

Current treatments include painkillers such as paracetamol or ibuprofen, hormonal contraceptives to regulate periods, and surgery to remove lesions or, in severe cases, the womb and ovaries. Niclosamide has gained attention as a potential new therapy because it can inhibit several signaling pathways involved in cell growth. Beyond treating parasitic infections, it is being investigated worldwide for conditions like kidney disease, COVID-19, diabetes, and various cancers.

A key challenge with niclosamide is its poor water solubility, which limits absorption into the bloodstream when taken orally, confining its effects to the gut and preventing it from reaching endometriotic lesions. To address this, researchers at Washington State University engineered a water-soluble nanoscale delivery system called a dendrimer—a tree-shaped structure containing niclosamide and folic acid. The folic acid targets immune cells characterized by the FR-beta protein, which are found in abundance within endometriotic lesions and are believed to contribute to disease symptoms.

In experiments involving mice genetically modified to develop endometriosis, the dendrimer-niclosamide complex was injected directly into the abdomen near the lesions. Two weeks after treatment, half of the mice receiving either low or high doses showed no detectable lesions, along with reduced pain sensitivity. These effects were sustained for at least two weeks.

Anjali Sharma, an associate professor of pharmaceutical sciences at the University of Michigan and a member of the research team, emphasized the importance of developing safe, long-term treatments that address the disease's root causes to improve quality of life for affected women. The team envisions that in the future, the drug could be administered as an injection every two weeks, circulating through the bloodstream and selectively delivering the medication to immune cells in lesions.

However, experts caution that findings remain preliminary. Andrew Horne, a professor of gynecology and reproductive sciences at the University of Edinburgh, noted that mice do not menstruate and do not naturally develop endometriosis, limiting the extent to which results can be extrapolated to humans. He also highlighted the study’s small sample size, short duration of up to three weeks, and focus on lesion reduction and pain behavior rather than long-term safety or efficacy. The frequency of treatment required and potential side effects in humans remain unknown, necessitating further research before clinical application.

While early results are encouraging and repurposing an existing drug could speed development, comprehensive human trials will be essential to determine whether this novel approach can provide an effective and safe treatment option for endometriosis.