Endometriosis is a difficult to manage condition associated with a significant disease burden. High levels of illicit cannabis use for therapeutic purposes have been previously reported by endometriosis patients in Australia and New Zealand (NZ). Although access to legal medicinal cannabis (MC) is available through medical prescription via multiple federal schemes, significant barriers to patient access remain. An anonymous cross-sectional online survey was developed and distributed through social media via endometriosis advocacy groups worldwide. Respondents were asked about legal versus illicit cannabis usage, their understanding of access pathways and legal status, and their interactions with health care professionals. Of 237 respondents who reported cannabis use with a medical diagnosis of endometriosis, 186 (72.0%) of Australian and 51 (88.2%) NZ respondents reported self-administering cannabis illicitly. Only 23.1% of Australian and 5.9% of NZ respondents accessed cannabis through a doctor's prescription, with 4.8% of Australian and no NZ respondents reporting to legally self-administer cannabis. Substantial substitution effects (>50% reduction) were observed in users of nonopioid analgesia (63.1%), opioid analgesia (66.1%), hormonal therapies (27.5%), antineuropathics (61.7%), antidepressants (28.2%) and antianxiety medications (47.9%). Of Australian respondents, 18.8% and of NZ respondents, 23.5% reported not disclosing their cannabis use to their medical doctor, citing concern over legal repercussions, societal judgment, or their doctors' reaction and presumed unwillingness to prescribe legal MC. Respondents self-reported positive outcomes when using cannabis for management of endometriosis, demonstrating a therapeutic potential for MC. Despite this, many are using cannabis without medical supervision. While evidence for a substantial substitution effect by cannabis was demonstrated in these data, of particular concern are the clinical consequences of using cannabis without medical supervision, particularly with regard to drug interactions and the tapering or cessation of certain medications without that supervision. Improving doctor and patient communication about MC use may improve levels of medical oversight, the preference for legal MC adoption over acquisition via illicit supply and reducing cannabis-associated stigma.