Clinical Insight | CED Clinic

A prospective cohort study published in BMC Complementary Medicine and Therapies in January 2026 found that medicinal cannabis reduced overall pelvic pain by more than 30% and worst pain scores by nearly 30% in 28 patients with endometriosis over 12 weeks, with concurrent improvements in sleep, anxiety, and health-related quality of life. Some patients were able to stop opioids entirely.

Endometriosis is estimated to affect roughly 190 million people worldwide. It is notoriously difficult to diagnose, often taking 7 to 10 years from first symptom to confirmed diagnosis, and current treatments, including hormonal therapies, NSAIDs, and laparoscopic surgery, work variably and carry significant side effect burdens of their own. Patients in Massachusetts and across the US routinely ask about cannabis as an alternative or adjunct, often after having exhausted conventional options. High-quality prospective data on cannabis in this population has been sparse. This New Zealand study is the first to follow endometriosis patients prospectively through a structured cannabis prescription protocol with weekly pain measurement, giving clinicians something more substantive to work with than survey data alone.

The study was conducted by Dr. Claire Henry and colleagues at the University of Otago, New Zealand, and published in BMC Complementary Medicine and Therapies in January 2026. Twenty-eight participants aged 18 to 50 with surgically or clinically diagnosed endometriosis were enrolled through self-referral to a specialist cannabis consultant in New Zealand, where medicinal cannabis is legally accessible by prescription. Participants were prescribed either CBD oil alone or CBD oil combined with dried cannabis flower, used as adjuncts to their existing standard medications. Pain was recorded weekly on a 0-to-10 numerical rating scale; health-related quality of life was measured using the Endometriosis Health Profile-30 (EHP-30) at baseline and at 12 weeks. Seventeen participants completed qualitative interviews at study completion. (Henry C, Cooper L, Adler H et al. BMC Complement Med Ther. 2026;26:60. DOI: 10.1186/s12906-025-05189-y)

Overall pelvic pain scores decreased from a mean of 5.46 to 3.77 over 12 weeks, a reduction of approximately 31%. Worst pain scores dropped from 7.62 to 5.38, a reduction of approximately 29%. The total EHP-30 score, which captures symptom burden across multiple quality-of-life domains, fell from 68.77 at baseline to 37.40 at 12 weeks, representing a clinically meaningful 46% improvement. Sleep and anxiety improved substantially alongside pain. Adverse events were described as limited; no serious adverse events were reported. Some participants were able to discontinue opioids during the study period. A minority of participants reported no benefit from CBD oil, with the dried cannabis flower formulation described as more effective for acute pain flares by those who used both. The authors describe the study as the first prospective cohort study of medicinal cannabis for endometriosis-related pain in New Zealand.

Endometriosis Pain and Cannabis: What This Study Adds and What It Cannot Yet Tell Us

Endometriosis is one of the most undertreated pain conditions in medicine. The diagnostic delay alone, averaging seven to ten years in most countries, reflects a historical failure to take menstrual and pelvic pain seriously as a clinical problem deserving rigorous investigation. By the time patients reach a specialist, many have already cycled through NSAIDs, hormonal contraceptives, GnRH agonists, and sometimes surgery, with incomplete or short-lived relief. Cannabis is one of the most common questions I hear from patients in this population, and it has been asked more urgently as dispensaries have become accessible and online communities have documented symptom relief at scale.

This New Zealand study is not an RCT. It is a prospective cohort study, which means there is no placebo arm, no randomization, and no way to isolate the cannabis effect from the concurrent standard treatments participants were also receiving, from the passage of time, from the attention of a specialist, or from the well-documented expectancy effects that accompany any cannabinoid-based therapy. All of that needs to be stated plainly. The study is not proof that cannabis treats endometriosis. It is evidence that a structured cannabis prescription protocol, layered onto existing care, was associated with meaningful pain reduction and quality-of-life improvement over 12 weeks in this group of patients.

The magnitude of the findings warrants attention. A 31% reduction in overall pelvic pain and a 46% improvement in EHP-30 scores are not trivial numbers. In a condition where conventional treatment responses are often partial and the side effect burden is substantial, numbers like that represent meaningful changes in how patients are able to live. Some participants stopped opioids during the study. That is a clinically significant endpoint, even in the absence of a control arm, because opioid discontinuation in a chronic pain population carries its own complexity and is not something that happens as a byproduct of time or attention alone.

The biology makes the result biologically plausible in ways that strengthen the interpretation. The endocannabinoid system plays a documented role in inflammatory pain signaling, uterine contractility, and central sensitization. CB1 and CB2 receptors are expressed in the uterus, ovaries, and peritoneal tissue. There is preclinical evidence that cannabinoids reduce prostaglandin synthesis and can modulate the neuroinflammatory cascades implicated in endometriosis-associated pain. THC’s action at CB1 receptors may reduce pain signal amplification at the spinal level; CBD’s anti-inflammatory profile may act on peripheral sensitization. None of that is proof of clinical efficacy on its own, but it is the kind of mechanistic grounding that makes the observed effect in this cohort something more than coincidence.

The heterogeneity of response is also clinically important and honestly reported here. CBD oil did not work for everyone. Some participants reported life-changing relief; others noticed no benefit. This is consistent with everything we observe in clinical practice with cannabinoid therapies more broadly. The right patient, the right formulation, the right dose, and the right timing all interact. Dried cannabis flower was described as most useful for acute pain flares, which is pharmacokinetically intuitive: inhaled cannabis has a faster onset and shorter duration than oral or sublingual preparations, making it better suited to breakthrough pain management than to sustained background coverage. Oil or tincture preparations fit better for continuous symptom control. That distinction is not often communicated clearly to patients, and it has real implications for how we frame the conversation in clinic.

Sleep and anxiety improvements equal to or exceeding the pain reductions in some participants reflect something the pain literature increasingly recognizes: pain is not a single-dimensional experience. In endometriosis, the sleep disruption from overnight pain cycles, the anxiety from medical uncertainty and diagnostic delay, and the pain itself form an interlocking system where improvement in one domain can cascade across the others. Cannabis addresses multiple components of that system simultaneously, which may partly explain why patients report overall quality-of-life benefit that exceeds what the raw pain number change would predict.

For Massachusetts patients with endometriosis who are asking about cannabis: endometriosis is not currently listed as a qualifying condition in Massachusetts’s medical cannabis program by name. However, the program includes chronic or debilitating disease or treatment-induced conditions that cause severe and persistent muscle spasms, severe pain, or nausea, and a physician can certify a patient based on symptom burden rather than diagnosis label. In practice, patients with endometriosis who meet those symptom criteria can access the program. The conversation about whether to try cannabis should be grounded in realistic expectations: symptom relief is possible, it is not guaranteed, the right product requires trial and iteration, and it should be used alongside rather than instead of coordinated gynecological care. This study supports that conversation. It does not replace the RCT that the field still needs.

Prior to this study, most cannabis and endometriosis evidence came from surveys and retrospective analyses. A 2021 study in PLOS ONE using the Strainprint app database found that 252 self-reported endometriosis patients across more than 16,000 cannabis sessions reported meaningful symptom improvement, with inhaled forms performing better for pain and oral forms for mood and gastrointestinal symptoms. The UK Medical Cannabis Registry analysis by Getter et al., published in the Australian and New Zealand Journal of Obstetrics and Gynaecology in 2026, found that longitudinal endometriosis patients on cannabis-based medicinal products showed improvements in pain VAS scores at 1, 3, and 6 months, with some effect maintained at 18 months. A scoping review by McLaren et al. in the same journal concluded that no completed RCTs exist yet for cannabis in endometriosis, though at least two registered trials are ongoing. The Henry et al. study adds the first prospective, longitudinal, specialist-supervised data with a structured outcome measurement protocol, which positions it as the strongest prospective evidence in this indication to date, while also underscoring how far the field still needs to travel.

From a clinical safety standpoint, the low adverse event rate in this study is consistent with other cannabis and chronic pain cohorts. The primary concerns for endometriosis patients using cannabis in Massachusetts include drug-drug interactions with hormonal therapies, particularly with estrogen-containing formulations that are CYP-metabolized, where CBD can inhibit CYP1A2 and CYP3A4 in ways that may alter hormone concentrations. Patients on opioid analgesics should be counseled on additive CNS depression risk, though the opioid-sparing effect documented in this and other cannabis pain studies suggests that supervised co-use may ultimately reduce total opioid burden. Patients with a personal or family history of psychosis or severe anxiety should be counseled about THC-containing formulations more carefully, particularly at higher doses.

A prospective cohort study follows participants forward in time with structured measurement, which is stronger than a retrospective survey but substantially weaker than a randomized controlled trial. The absence of a control arm means we cannot determine how much of the improvement was attributable to cannabis, how much to the other treatments participants continued using, and how much to placebo or expectancy effects — which are particularly high in cannabis research due to the drug’s psychoactive profile and the positive media environment surrounding it. A placebo response in a cohort like this can account for 10 to 25 percentage points of improvement. The observed pain reductions in this study (31% overall, 29% worst) exceed typical placebo bounds, but without a control arm that judgment is inferential, not confirmatory. The EHP-30 improvement (46%) is striking and may reflect the compound effects of sleep and anxiety improvement alongside pain reduction.

Survey and retrospective data consistently show that endometriosis patients who use cannabis report meaningful symptom improvement, with pain, sleep, and mood as the most commonly cited benefits. Preclinical data support plausible mechanisms involving CB1 and CB2 receptor activity in uterine and peritoneal tissue. The UK Medical Cannabis Registry data show sustained benefit at 18 months in a minority of patients, which is important for thinking about durability. The McLaren et al. scoping review confirmed that no completed RCTs exist, meaning this prospective cohort, despite its limitations, represents the most structured longitudinal data available in this specific population. The DREAMLAND trial and at least one Australian RCT are registered and ongoing; their results will substantially reshape how cannabis is discussed in endometriosis care. Until then, studies like this serve as the best available clinical scaffolding for a conversation that patients are going to have regardless of whether clinicians engage with it.

Yes, in multiple directions. Had the study included a control group receiving standard care without cannabis, the apparent effect size would likely have been smaller, because regression to the mean and natural fluctuation in pain would have been captured in both arms. Had the study excluded participants who were concurrently starting or changing other medications, the cannabis-specific effect would have been cleaner. Had the investigators separated the CBD-only cohort from the CBD-plus-flower cohort for independent analysis, we could have seen whether the formulations produced meaningfully different outcomes. And had the sample been larger, subgroup analysis by endometriosis staging, pain phenotype, and prior treatment history would have been possible and clinically useful. As described, the study cannot answer those questions. The honest contribution is a signal, not a confirmation.

Misreading 1: “This proves cannabis treats endometriosis.” It does not. It shows that in a small prospective cohort of highly motivated participants prescribed cannabis by a specialist, pain and quality-of-life scores improved substantially over 12 weeks. Without a control arm, causation cannot be established.

Misreading 2: “CBD is the answer for endometriosis.” The study found that CBD oil alone did not work for everyone, and that dried cannabis flower (which contains THC) was preferred for acute pain flares. The suggestion that CBD is the therapeutic active ingredient without THC is not supported by this data or by the broader pharmacological literature on pain.

Misreading 3: “I can replace my hormonal therapy with cannabis.” Participants in this study used cannabis alongside, not instead of, their existing standard medications. Cannabis in this context was an adjunct. Discontinuing hormonal or surgical management without medical guidance is not supported by any evidence in this or any adjacent study.

The first prospective cohort study of medicinal cannabis for endometriosis-related pain found meaningful reductions in pelvic pain and symptom burden over 12 weeks, with some patients able to reduce or discontinue opioids. The biological plausibility is strong, the effect sizes are larger than typical placebo response, and the study’s honest reporting of non-responders adds credibility rather than undermining it. What this study cannot do is establish causation or replace the RCT evidence that the field still lacks. For clinicians in Massachusetts and beyond, it adds the most structured prospective data available to a conversation that endometriosis patients are going to have with or without us. Being prepared to engage it accurately is clinical responsibility, not optional.

Q: Can I use cannabis for my endometriosis pain?
This is something to work through with your gynecologist and, ideally, a physician familiar with cannabis medicine. What this study adds is the most structured prospective evidence to date that cannabis can be associated with meaningful pain reduction in endometriosis, particularly when used as an adjunct to existing care under specialist supervision. It does not replace hormonal therapy, surgical management, or physical therapy. In Massachusetts, endometriosis patients may qualify for the medical cannabis program based on symptom severity, even though endometriosis is not listed by name as a qualifying condition.

Q: Should I use CBD oil or dried flower?
The study found that CBD oil was helpful for some and ineffective for others. Dried cannabis flower (which contains THC) was described as more effective for acute pain flares, which makes pharmacological sense given its faster onset. For sustained background pain management, oil or tincture preparations with titrated dosing are generally more practical. What formulation, ratio, and dose fits your situation depends on your symptoms, your other medications, and your response over time. That requires individualized guidance, not a general recommendation.

Q: Is cannabis safe to use with my endometriosis medications?
Depends on what you are taking. CBD can inhibit CYP1A2 and CYP3A4, which may affect the metabolism of estrogen-containing hormonal therapies and some analgesics. Cannabis also has additive CNS effects with opioid pain medications. These interactions are generally manageable, but they need to be disclosed to and monitored by your prescribing physicians. Do not start cannabis without informing the providers managing your other treatments.

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