Cannabis in Pain Therapy: Evidence and Practice

Pain is the most common indication for medical cannabis in Germany – approximately 76 percent of all prescriptions recorded in the BfArM companion survey were for pain diagnoses. But how strong is the evidence? Which types of pain respond particularly well to cannabis? And what does optimal dosing look like? This article provides a comprehensive, evidence-based overview of the role of cannabis in modern pain therapy.

## Pain Physiology and the Endocannabinoid System

Understanding the effect of cannabis on pain requires a basic grasp of pain physiology and the role of the endocannabinoid system (ECS) in pain modulation.

### Pain Transmission

Pain is mediated through a complex network of peripheral nociceptors, afferent nerve fibers, the spinal cord, and higher brain centers. We distinguish nociceptive pain (triggered by tissue damage), neuropathic pain (caused by nerve damage or dysfunction), and nociplastic pain (central sensitization without clear tissue damage). Chronic pain develops when acute pain mechanisms are not adequately resolved and self-reinforcing pain circuits become established, leading to central sensitization.

### The ECS in Pain Modulation

CB1 receptors are densely expressed in the dorsal horn of the spinal cord, in the periaqueductal gray (PAG), and in the rostral ventromedial medulla (RVM) – all key structures of descending pain modulation. When CB1 receptors are activated by endogenous or exogenous cannabinoids, they inhibit the release of excitatory neurotransmitters such as glutamate and substance P. This reduces the transmission of pain signals at the spinal level. CB2 receptors on immune cells and microglia modulate the neuroinflammatory component of chronic pain. Activated microglia release proinflammatory cytokines that contribute to the maintenance of chronic pain. CB2 activation inhibits these proinflammatory processes.

Endocannabinoids such as anandamide and 2-arachidonoylglycerol (2-AG) are synthesized on demand and serve as retrograde signaling molecules that modulate synaptic transmission. Their levels are often altered in chronic pain patients, supporting the hypothesis of clinical endocannabinoid deficiency (CED).

## Neuropathic Pain

Neuropathic pain – caused by nerve damage or dysfunction – is considered the best-supported indication for cannabis in pain therapy.

### Study Evidence

Several systematic reviews and meta-analyses support the efficacy of cannabinoids for neuropathic pain. A 2018 Cochrane review analyzed 16 randomized controlled trials (RCTs) and found moderate evidence for clinically relevant pain reduction with cannabinoids (Number Needed to Treat, NNT: 11). The NNT is higher than for some first-line therapies but comparable to other third-line medications. The IASP (International Association for the Study of Pain) rated the evidence for cannabinoids in neuropathic pain as "inconclusive or insufficient" in 2021 and issued no recommendation – but also no general discouragement. This reflects methodological limitations of existing studies rather than necessarily a lack of efficacy.

A Canadian multicenter study (Lynch and Campbell, 2011) showed that inhaled cannabis at three different THC concentrations (2.5%, 6%, and 9.4%) produced significant pain reduction in HIV-associated neuropathy. The highest concentration achieved the best analgesia but also carried more side effects.

### Practice Recommendations

In clinical practice, neuropathic pain is typically treated with THC-dominant preparations. Dosing follows the "start low, go slow" principle: begin with 2.5 mg THC once or twice daily, increase by 2.5 mg every 3–7 days until optimal dosing is reached. Most patients achieve satisfactory analgesia at 10–30 mg THC daily. CBD can be used adjunctively, as it has independent analgesic mechanisms (TRPV1 modulation, adenosine reuptake inhibition).

## Chronic Back Pain

Chronic back pain affects up to 85 percent of adults at least once in their lifetime and is one of the leading causes of work disability worldwide.

### Evidence for Cannabis

The data on cannabis for chronic back pain is more heterogeneous than for neuropathic pain. A prospective observational study from Israel (Aviram and Samuelly, 2017) examined 274 patients with treatment-resistant back pain who were treated with medical cannabis. After six months, 56 percent of patients reported significant pain reduction (at least 30% on the visual analog scale). Notably, opioid consumption also decreased: 44 percent of patients who previously took opioids were able to reduce their dose or discontinue opioids entirely.

The German BfArM companion survey confirmed these observations: back pain was the second most common individual diagnosis, and treating physicians rated the therapeutic outcome as good to very good in the majority of cases.

### Multimodal Therapy

Cannabis should not be used as monotherapy for chronic back pain but as part of a multimodal treatment concept encompassing physiotherapy, exercise, psychological pain therapy, and where appropriate, interventional procedures. Cannabis can facilitate mobilization by reducing pain and muscle tension and improve participation in active therapies.

## Fibromyalgia

Fibromyalgia is a chronic pain syndrome characterized by widespread pain, fatigue, sleep disturbances, and cognitive impairment. Its pathophysiology is understood as central sensitization, and conventional therapies often provide inadequate relief.

### Cannabis for Fibromyalgia

The clinical endocannabinoid deficiency (CED) theory postulates that fibromyalgia is linked to ECS dysfunction. Several observational studies show positive effects of cannabis in fibromyalgia. An Israeli study (Sagy et al., 2019) examined 367 fibromyalgia patients over six months of cannabis therapy. The results were impressive: 81.1 percent reported moderate to strong pain improvement, 73.4 percent reported improved sleep quality, and 80.8 percent reported improved general well-being.

A Dutch RCT (van de Donk et al., 2019) tested four different cannabis preparations in fibromyalgia patients using a crossover design. The Bediol cultivar (THC 6.3%, CBD 8%) showed the best efficacy with good tolerability, pointing to the importance of the THC-CBD ratio and the entourage effect.

### Dosing Guidelines for Fibromyalgia

Fibromyalgia patients often respond sensitively to THC. Starting with CBD-dominant or balanced preparations is recommended. Evening administration can address both sleep and pain. Dose escalation should be particularly cautious. Terpenes such as myrcene (muscle relaxant) and linalool (anxiolytic) may provide additional benefit.

## Migraine and Headaches

Cannabis has a long historical tradition in migraine treatment – in the 19th century, it was among the most commonly used migraine medications.

### Current Study Evidence

A retrospective analysis by Cuttler et al. (2019) evaluated over 12,200 migraine episodes documented by patients using a tracking app. Inhaled cannabis reduced headache intensity by an average of 47.3 percent for migraine and 49.6 percent for tension headaches. Interestingly, efficacy for migraine was somewhat higher in men than in women.

A prospective study at the University of Haifa (Aviram et al., 2020) showed a reduction in monthly migraine days averaging 42 percent among 97 migraine patients receiving cannabis therapy. Additionally, analgesic consumption and the intensity of individual attacks decreased significantly.

### Mechanisms in Migraine

Cannabinoids intervene in migraine pathophysiology at multiple levels: THC inhibits serotonin (5-HT) release from platelets, modulating trigeminovascular activation. CBD inhibits anandamide uptake, which itself has antinociceptive properties. Terpenes like beta-caryophyllene act as CB2 agonists with anti-inflammatory effects. Cannabinoids modulate the release of CGRP (Calcitonin Gene-Related Peptide), the key mediator of migraine.

### Prophylaxis vs. Acute Therapy

For migraine prophylaxis, oral formulations (dronabinol drops, CBD oil) with regular intake are suitable. For acute therapy, inhaled cannabis (vaporization) offers rapid onset within minutes. A combination of prophylactic oral intake and acute inhalation as needed can be effective.

## THC vs. CBD in Pain Therapy

The question of whether THC or CBD is more effective for pain cannot be answered generically – both cannabinoids have different mechanisms of action and complement each other in many cases.

### THC in Pain Therapy

THC is the more potent analgesic of the two cannabinoids. It acts through CB1-mediated inhibition of pain transmission, modulation of the affective pain component (via limbic structures), peripheral CB2 activation with anti-inflammatory effects, and muscle relaxation. THC is particularly effective for neuropathic pain, tumor pain, and spasticity-associated pain. The psychoactive effect can improve pain coping in some patients (through distraction and mood modulation) but may impair daily functioning in others.

### CBD in Pain Therapy

CBD exerts analgesic effects through different mechanisms: TRPV1 modulation (vanilloid receptor) affecting pain perception; inhibition of anandamide reuptake and the FAAH enzyme, enhancing endocannabinoid signaling; adenosine A2A receptor activation with anti-inflammatory effects; inhibition of TNF-alpha and other proinflammatory cytokines; and glycine receptor modulation affecting pain processing. CBD is particularly promising for inflammatory pain, arthritis, and inflammatory neuropathies. Its advantage lies in the absence of psychoactive effects, facilitating everyday use.

### Synergistic Effects

Clinical observations and preclinical data show that the combination of THC and CBD produces synergistic effects. CBD modulates THC activity at the CB1 receptor (allosteric modulation), reduces THC side effects such as anxiety and cognitive impairment, and enhances analgesic action through complementary mechanisms. The oromucosal spray nabiximols (Sativex), containing THC and CBD in a 1:1 ratio, deliberately leverages this synergy. In practice, many patients achieve the best balance between analgesia and tolerability with a THC:CBD ratio of 1:1 to 2:1.

## Dosing: Start Low, Go Slow

The "start low, go slow" principle is essential in cannabinoid-based pain therapy. Individual response rates vary considerably, and overly rapid dose escalation leads to avoidable side effects.

### Titration Protocol

Initiation typically proceeds as follows: week one, 2.5 mg THC in the evening; week two, 2.5 mg THC morning and evening; then weekly increases of 2.5 mg per single dose. The target dose usually ranges from 10–30 mg THC daily, divided into two to three administrations. With CBD-dominant preparations, titration can proceed more quickly since psychoactive effects are not a concern. A typical CBD titration protocol begins with 10 mg twice daily and increases weekly by 10 mg up to doses of 50–200 mg daily.

### Special Patient Populations

Elderly patients (over 65) should start with even lower doses (1.25 mg THC) and titrate more slowly, as they are more sensitive to central side effects. Patients with liver disease require dose adjustment, as THC and CBD are metabolized hepatically. Patients with psychiatric comorbidity (especially anxiety disorders or psychotic disorders) require particular caution with THC-containing preparations.

## Interactions with Other Pain Medications

Combining cannabis with other pain medications requires knowledge of potential interactions.

### Opioids

The combination of cannabis with opioids is interesting for several reasons. Preclinical data show synergistic analgesic effects that could enable opioid dose reduction. Several observational studies report 40–60 percent reductions in opioid consumption with cannabis co-medication. However, additive sedation requires caution, especially during the adjustment phase. There are no clinically relevant pharmacokinetic interactions at the CYP450 level between THC and most opioids.

### NSAIDs (Non-Steroidal Anti-Inflammatory Drugs)

The combination with NSAIDs such as ibuprofen or diclofenac is generally unproblematic. Theoretically, additive gastrointestinal effects could occur, but this is rarely clinically relevant. Cannabis may in some cases reduce NSAID requirements.

### Anticonvulsants and Antidepressants

Gabapentin and pregabalin (commonly used for neuropathic pain) can cause additive sedation and dizziness. Amitriptyline (also used in pain therapy) shows additive anticholinergic and sedative effects with cannabis. SNRIs such as duloxetine have no known relevant interactions.

## Patient Experiences and Therapy Adherence

The patient perspective is particularly relevant for cannabis pain therapy, as subjective pain relief and quality of life are the primary therapeutic goals.

### Typical Experiences

Patient reports consistently show that pain reduction is often incomplete but sufficient to improve daily functioning. Many patients describe that cannabis does not primarily reduce pain intensity but rather diminishes the emotional burden of pain – the pain is "still there but bothers less." Improvement in sleep quality is cited by many patients as one of the most important additional effects. Initial titration can be challenging, and some patients discontinue therapy prematurely due to side effects.

### Adherence and Long-Term Course

Therapy adherence with medical cannabis at 60–80 percent after one year is relatively high – comparable to or better than many other chronic pain therapies. Reasons for discontinuation include side effects (primarily dizziness and cognitive impairment), insufficient efficacy, stigmatization, cost (when insurance coverage is denied), and logistical difficulties (prescription availability, pharmacy supply). Long-term data over two to five years show that the majority of patients achieve a stable dose without requiring continuous dose escalation. This distinguishes cannabis from opioids, where tolerance development frequently leads to dose increases.

## Legal and Practical Aspects

### Prescription and Insurance Coverage

Since the 2017 legislative change, any physician in Germany can prescribe cannabis on a controlled substance prescription. For insurance coverage by statutory health insurance, an application to the health insurance fund is required. The approval rate is approximately 60–65 percent for initial applications. If denied, an appeal is worthwhile, as the success rate in appeal proceedings is approximately 40 percent.

### Driving Fitness

Patients treated with medical cannabis are generally permitted to participate in road traffic, provided they are able to operate a vehicle safely. Medical assessment and stable dosing are prerequisites. During the adjustment phase and dose changes, driving should be avoided.

## Summary and Outlook

Cannabis has established itself as a valuable addition to the pain therapy repertoire. The best evidence exists for neuropathic pain, followed by spasticity-associated pain and cancer-related pain. For fibromyalgia and migraine, observational data are promising, but randomized trials remain limited. The future of cannabinoid-based pain therapy lies in personalization: genetic testing could predict individual response rates, standardized cannabinoid-terpene profiles could improve reproducibility, and targeted combinations of cannabinoids and conventional analgesics could exploit synergistic effects.