Medical Cannabis and Chronic Pain: Scientific Evidence
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The use of medicinal cannabis for the treatment of chronic pain has gained scientific legitimacy in recent years, backed by growing clinical evidence demonstrating its efficacy in patients refractory to conventional treatments. In Spain, the approval of Royal Decree 903/2025 officially recognizes the therapeutic potential of cannabinoids for this and other pathologies.
How cannabis acts on chronic pain
The human body has an endocannabinoid system that regulates fundamental functions such as pain, mood, sleep, and immune response. Cannabinoids from medicinal cannabis, primarily THC (tetrahydrocannabinol) and CBD (cannabidiol), interact with this system, reducing pain signals and decreasing inflammation.
Studies show that medicinal cannabis is especially effective for neuropathic nerve pain and pain caused by conditions such as multiple sclerosis, rheumatoid arthritis, and fibromyalgia. Cannabinoids modulate pain perception at the central and peripheral nervous system levels, offering relief when other medications fail.
Available scientific evidence
Systematic reviews have summarized positive findings of the analgesic effect of cannabinoids in the management of chronic pain. Studies include research with Nabiximols (Sativex®), Nabilone, cannabis extract spray, Dronabinol, and vaporized cannabis.
A study with rheumatoid arthritis patients treated with oral Sativex® for 5 weeks showed a significant improvement in pain during movement, at rest, and in sleep quality. The guideline published by the medical journal BMJ in 2021 recommends non-inhaled medicinal cannabis when standard therapy is not sufficient to relieve pain.
Research on CBD cannabinoids as an analgesic shows promising results at doses of 75 mg (1 ml or 20 drops) every 8-12 hours, with a treatment duration of 2 to 8 weeks. Patients report a considerable reduction in symptoms and an improvement in quality of life.
Demonstrated therapeutic benefits
Medicinal cannabis offers multiple benefits for patients with chronic pain:
Pain relief: Significant reduction in pain intensity and greater overall comfort.
Improved sleep: Pain frequently disrupts night rest, and cannabis can substantially improve sleep quality.
Opioid reduction: For many patients, cannabis allows for a decrease in dependence on opioid analgesics, which carry high risks of addiction and serious side effects.
Mood stabilization: Chronic pain frequently causes depression or anxiety, and cannabis can help stabilize emotional state.
Anti-inflammatory effect: Cannabinoids reduce inflammation, which often contributes to chronic pain in rheumatic and autoimmune pathologies.
Approved indications in Spain
Royal Decree 903/2025 establishes that medicinal cannabis can be prescribed for refractory chronic pain, when conventional treatments have not been effective. Other initial indications include:
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Epilepsy refractory to conventional treatments
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Spasticity associated with multiple sclerosis
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Nausea and vomiting caused by chemotherapy
The list of indications is not exhaustive and may be expanded as scientific evidence progresses and official AEMPS monographs are published.
Side effects and precautions
Although generally well-tolerated, medicinal cannabis can produce side effects:
Common and transient effects:
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Dry mouth
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Red eyes
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Increased appetite
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Mild euphoria
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Reduced alertness
Cardiovascular effects:
THC can increase heart rate and cause changes in blood pressure. Patients with a history of heart disease should only use cannabis under meticulous medical supervision.
Psychological effects:
In predisposed individuals, cannabis can cause anxiety, panic attacks, or mild psychotic symptoms, especially with high doses of THC. Abrupt discontinuation after prolonged use can cause withdrawal symptoms such as restlessness, irritability, and insomnia.
Drug interactions:
Cannabis can interact with other drugs, especially central nervous system depressants such as alcohol, benzodiazepines, or ketamine, increasing sedation and the risk of adverse effects.
Documented clinical cases
Clinical case reports show successful practical applications. Patients aged between 51 and 78 with rheumatic pathologies such as arthritis and articular osteoarthritis, who did not find relief with conventional analgesics and anti-inflammatories, experienced significant improvement with CBD cannabinoids.
Research on patients with irritable bowel syndrome (IBS) showed that the use of medicinal cannabis reduced hospital stays from 3.6 to 2.8 days and decreased total costs from USD 23,624 to USD 20,388. The authors concluded that medicinal cannabis can reduce hospital healthcare utilization in patients with chronic visceral pain.
Limitations and research needs
Despite promising results, the available literature is not yet conclusive. Systematic reviews acknowledge that more research is needed to establish definitive protocols on risks, benefits, optimal dosages, and treatment duration.
The available cannabinoids show a modestly effective and safe analgesic role, providing a reasonable therapeutic option in the treatment of chronic non-cancer pain when other approaches fail. However, medicinal cannabis should not be considered a unique monotherapy, but rather an integrated complement in a multidisciplinary pain management approach.
Access in Spain: hospital model
With the new Spanish legal framework, patients with refractory chronic pain will be able to access medicinal cannabis exclusively through specialized prescription and dispensing in hospital pharmacies. The preparations will be magistral formulas elaborated with rigorous pharmaceutical standards, guaranteeing precise dosages of THC and CBD.
Regular monitoring by the medical and pharmaceutical team will allow for dose adjustment and real-time assessment of the benefit-risk balance, maximizing therapeutic efficacy and minimizing adverse effects in each individual patient.
