A 49-year-old woman was diagnosed with an ER + , PR-, HER2 + , BRCA- invasive ductal carcinoma which progressed metastatically to include bone, liver, and lymph node involvement. Standardised care included a 26-month treatment period with targeted chemotherapy and a ketogenic diet. The patient also began a course of cannabinoid-based therapy, consisting initially of a titrated high-dose protocol of mixed cannabidiol (CBD) and d9-tetrahydrocannabinol (THC) chemotypes, as well as psilocybin-assisted psychotherapy at macro and intermittent micro-doses. At the end of the five-month treatment period PET/CT investigations revealed no evidence of metastatic disease and chemotherapy was withdrawn. A one year follow up CT investigation concluded no evidence of residual or recurrent disease. A recurrence of disease was noted at 18 months follow up. Over these 18 months the cannabis regimen was titrated down to 60% of the initial protocol. This was subsequently increased to the initial dosing protocol following detection of recurrent disease and this titration occurred over a 10-month period where it remained stable. 16 months following the detection of recurrence of disease, favourable results were observed in the patient with evidence of receding cancer progression. Over the last 15 years there has been a considerable body of in-vitro and in-vivo evidence supporting the anti-neoplastic properties of cannabinoids and more recently psychedelics. Indeed, growing anecdotal and real-world evidence is reported of the therapeutic effect of cannabinoids and psychedelics in reducing both tumour proliferation and aiding as a palliative medicine to treat pain and psychological distress associated with cancer and chemotherapy. The data presented here indicate the potential therapeutic utility of such adjunctive pharmacological interventions in an individual with metastatic breast cancer.