The goal of this clinical trial is to evaluate the effects of cannabidiol in patients with end-stage metastatic castration-resistant prostate cancer (mCRPC).

The primary objective is to determine whether cannabidiol (CBD) treatment can reduce the need for opioids in patients with end-stage mCRPC.

Additionally, the study will assess a range of clinical endpoints in patients with end-stage mCRPC, including:

1. The efficacy of CBD treatment in alleviating pain
2. The efficacy of CBD treatment in reducing the need for non-opioid medications and concomitant therapies
3. The impact of CBD treatment on physical activity and quality of life
4. The anti-inflammatory and potential anti-tumor properties of CBD
5. The safety of CBD treatment

Patients from Department of Urology, Aalborg University Hospital will be included. Participants will be treated with either CBD (200 mg) or placebo (0 mg) three times daily for nine weeks. At baseline, halfway and end of trial, participants will use an activity tracker and complete questionnaires regarding pain and quality of life and provide blood samples to measure inflammation and tumor activity. Also, they will complete a daily dairy regarding the study drug and intake of pain medication. Adverse events will be assessed by Common Terminology Criteria for Adverse Events.

Inclusion Criteria:

• Patients diagnosed with mCRPC as documented by increasing PSA despite optimally attempted treatment, and no other therapeutic options.
• Treatment-resistance or ineligible to standardized cancer therapy, incl. medical and surgical castration, chemotherapy, and super hormone treatment.
• Minimum 3 months since radiation therapy, if part of treatment.
• Perception of pain
• Daily use of Morphine (ATC: N02AA01) (10mgx2) in relief of pain.

Exclusion Criteria:

• Perception of worst pain <4.0 on the NRS within the last week prior to baseline visit70. (Inclusion if: three days with highest pain intensity have an average of ≥4.0 and/or three days where pain intensity is at least 4.0).
• Pattern of short duration of response to all previous treatment regimens (<6 months) clinically assessed by the investigator.
• Eastern Cooperative Oncology Group (ECOG) performance status >3 (scale 0-5).
• Change in regular use of conventional pain medication within two weeks prior to baseline visit.
• A history of substance use disorder.
• Functional liver insufficiency with an alanine transaminase (ALT) >2X ULN and/or bilirubin >2X ULN assessed by a blood sample taken at screening.
• Renal failure with an estimated glomerular filtration rate (eGFR) < 30mL/min/1,73m2 assessed by a blood sample taken at screening.
• Known heart failure - New York Heart Association III - IV (scale I-IV)71.
• Known severe chronic obstructive lung disease (Forced Expiratory Volume in the first second (FEV1) <50%)72.
• Use of THC-containing cannabis products measured by a urine sample at screening.
• Any chronic or acute systemic medical condition that, in the opinion of the investigator, may pose a risk to the safety of the patient or may interfere with compliance or the assessment of efficacy in this trial.
• Hypersensitivity to the active substance
• Not capable of giving informed consent.
• Not capable of understanding, write or read Danish.

Only biological men