Is HMI-115 Considered a Safe Option, or Does It Have Strong Side Effects?

HMI-115 has drawn increasing attention in recent years as a possible new pathway in hair loss treatment. Unlike minoxidil, which stimulates blood flow to the scalp, or finasteride, which blocks the conversion of testosterone into dihydrotestosterone, HMI-115 belongs to a completely different category. It is a monoclonal antibody that blocks the prolactin receptor, and its developer describes it as a non-hormonal drug: it is designed to interrupt prolactin signalling at the receptor without suppressing the sex hormones. Because the drug is still investigational and delivered by injection, the safety question is about what trials have measured so far, and about how much is still unmeasured.

What Makes HMI-115 Different?

The main interest in HMI-115 lies in its mechanism. Prolactin is best known for its role in breastfeeding, but the prolactin receptor is also present in hair follicles and in endometrial tissue. HMI-115 binds that receptor and blocks prolactin's signal. Hope Medicine, the developer, describes this as the first prolactin-receptor blocker taken into human trials, and presents it as an alternative to hormone-suppressing drugs precisely because it is not intended to lower estrogen, progesterone or testosterone. Researchers became interested in this pathway after laboratory and animal work suggested that prolactin signalling influences hair follicle cycling. Whether that translates into a durable benefit in people is what the Phase 2 programme was designed to answer, and the alopecia results have not been published in a peer-reviewed journal.

Assessing safety here means separating three things: what a published trial measured, what a company press release asserted, and what has not been studied at all. Most of the human data on HMI-115 comes from company-sponsored work, so the early findings should be read with that in mind.

2021: Trials in Endometriosis Patients

In October 2021, Hope Medicine began a randomised, multicentre, double-blind, placebo-controlled Phase 2 trial of HMI-115 in premenopausal women with moderate to severe endometriosis-associated pain (NCT05101317). Endometriosis is a painful condition where tissue similar to the lining of the uterus grows outside it, causing inflammation and infertility. Participants received subcutaneous injections every two weeks at 60 mg, 120 mg or 240 mg, or placebo, over a 12-week treatment period. Results were published in 2025 in The Lancet Obstetrics, Gynaecology & Women's Health. The trial reported a reduction in pain scores, and the authors described the tolerability profile as acceptable, with no treatment-related serious adverse events reported. The company's summary of the same trial states that pain was relieved without disturbing the participants' sex hormones. The key limitation for this article is that the trial did not include hair loss patients, so its safety profile cannot simply be assumed to carry over. It also covered 12 weeks of treatment, which says nothing about long-term use.

Preclinical Studies in Animals

Before human testing, prolactin-receptor blockade was studied in animals, including work in a mouse model of endometriosis and in primates. Animal studies of this kind provide valuable insights but are never definitive, since human physiology can respond differently, and published animal work on this receptor has focused mainly on endometrial tissue rather than on scalp hair. No published animal study establishes a long-term hair-growth or hormonal safety profile for HMI-115, so the drug's animal record should not be described as reassuring or as alarming.

2023-2024: Early Trials in Pattern Hair Loss

Hope Medicine ran an open-label Phase 1b study in Australia in patients with androgenic alopecia, enrolling 12 men and 4 women over 24 weeks, and announced the outcome in a press release in January 2024. The company reported a mean increase of 14 non-vellus hairs per square centimetre in the men and described the antibody as safe and well tolerated; it did not release results for the four women. A larger placebo-controlled Phase 2 study in men followed in China (NCT06118866): 192 participants, 24 weeks of treatment, with arms of 120 mg every four weeks, 240 mg every four weeks and 240 mg every two weeks against placebo. That study is registered as completed. No peer-reviewed publication of either alopecia study has appeared, and no adverse-event table for the alopecia trials has been made public. Statements about how HMI-115 feels to take for hair loss therefore rest on company communications, not on reviewed data.

Why the Non-Hormonal Mechanism Matters for Safety

Unlike minoxidil, which is applied topically and has largely local effects, HMI-115 is injected and circulates through the body. That alone makes its safety question systemic rather than local. What the drug is not designed to do matters here: it does not act on the gonadotropin-releasing hormone axis, and the published endometriosis trial and the company both report that sex hormone levels were not suppressed. Menopause-like symptoms such as hot flashes and irregular bleeding are characteristic of hormone-suppressing endometriosis drugs, and they have not been reported as the profile of HMI-115. What remains unknown is more relevant: prolactin has roles in immune regulation, lactation and metabolism, and no published study has followed HMI-115 recipients for years. Long-term safety is genuinely unestablished rather than reassuring.

The Verdict: Well Tolerated So Far, but Unfinished

So, is HMI-115 a safe option or one with strong side effects? Neither label is supported yet. The one peer-reviewed trial, in endometriosis, reported an acceptable tolerability profile over 12 weeks with no treatment-related serious adverse events. The alopecia trials have reported no safety concerns in company statements, but those statements have not been published or independently reviewed, and the Phase 2 dataset is not public. There is no long-term safety data in any population, and there is no released safety data at all for women treated for hair loss.

HMI-115 is an experimental injectable antibody. It is not approved for hair loss anywhere, it cannot be obtained outside a clinical trial, and its long-term safety is unknown. Talk to a doctor or pharmacist before starting, stopping or combining any hair-loss treatment, and do not treat an investigational biologic as an over-the-counter option. Until large, independent, long-term results are published and reviewed, the accurate description is promising and unproven, not proven safe and not proven harmful.

References

Hope Medicine. HMI-115: what we know so far - background on mechanism and early phase information, as summarised by Perfect Hair Health (published 9 May 2024, updated 23 Oct 2024). https://perfecthairhealth.com/hmi-115-what-we-know-so-far/

Safety and efficacy of subcutaneous injection with HMI-115 versus placebo in endometriosis-associated pain in premenopausal women: a multicentre, double-blind, randomised, proof-of-concept phase 2 trial. The Lancet Obstetrics, Gynaecology & Women's Health (2025). https://www.thelancet.com/journals/lanogw/article/PIIS3050-5038(25)00032-9/abstract

ClinicalTrials.gov. Phase 2 study of HMI-115 in women with moderate to severe endometriosis-associated pain (NCT05101317). https://clinicaltrials.gov/study/NCT05101317

Hope Medicine. Positive Outcome from a Phase Ib Study in Australia Treating Patients with Androgenic Alopecia (January 2024), as carried by BioSpace. https://www.biospace.com/positive-outcome-from-a-phase-ib-study-in-australia-treating-patients-with-androgenic-alopecia

ClinicalTrials.gov. Phase 2 study of HMI-115 in male androgenetic alopecia over a 24-week treatment period (NCT06118866). https://clinicaltrials.gov/study/NCT06118866

Hope Medicine. Announces US FDA Clearance for Phase II Clinical Trial of A First-in-class Monoclonal Antibody, HMI-115, in AGA Alopecia. https://www.hopemedinc.com/company-release-5