The Scientist - USA (2020-04)

04.2020 | THE SCIENTIST 11

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Cannabis May Not Be

a Cancer Pain Panacea

Studies are lacking, and in the high-quality research that scientists have

published, the results are not promising.

BY JASON BOLAND AND ELAINE BOLAND

C

annabis products, in the form of

the plant’s flowers, isolated canna-

binoids, or synthetic cannabinoid

preparations, are increasingly used as medi-

cine, especially with the intention of treat-

ing cancer-related ills. But there is a serious

dearth of rigorous data to support many of

these indications.

There is no randomized controlled

evidence for the effect of any cannabinoid

(the active chemicals in medicinal canna-

bis) on cancer-related pain. Indeed, there

is evidence that a product containing an

equal ratio of cannabidiol (CBD) to tet-

rahydrocannabinol (THC), the psycho-

active ingredient of marijuana, does not

reduce cancer-related pain compared with

placebo, and that the CBD:THC combo

treatment could lead to more side effects.

To take the next step in strengthening

the evidence clinicians use to support their

practice, we and our collaborators recently

published a systematic literature review

in BMJ Supportive & Palliative Care that

analyzed data from five recently published

high-quality studies that assessed the

effect of cannabinoids for cancer-related

pain. Uncontrolled studies with no pla-

cebo group or other comparator tend

to overestimate effects of interventions,

so we rigorously searched the literature

specifically for randomized trials assess-

ing the effects of cannabinoids versus a

placebo on pain in patients with cancer.

All published studies that we found used

Sativex, a spray consisting of CBD:THC

at a 1:1 ratio, compared with placebo in

patients on prescription opioids for can-

cer pain. We could detect no difference

between cannabinoids and placebo in

reducing pain scores across the five stud-

ies. Moreover, cannabinoids carried a

higher risk of adverse events, especially

somnolence and dizziness, when com-

pared with placebo.

No other cannabinoid or combina-

tion of cannabinoids has been studied in

a randomized trial for cancer pain, so no

data are available on these agents; as such,

they could not be included in our system-

atic review. Therefore, the effect (and side

effects) of other cannabinoids or combina-

tions compared with placebo or other treat-

ments is unknown. In addition, our sys-

tematic literature review was only looking

for studies of cancer pain. This review did

not assess the use of cannabinoids for non-

pain indications, such as poor appetite, in

patients with cancer.

That’s not to say that cannabinoids

don’t serve some medicinal purposes. The

UK’s National Institute for Health and

Care Excellence (NICE) guideline provides

a list of cannabis-based products backed

with evidence of their effectiveness; treat-

ments include the orally active synthetic

cannabinoid nabilone for intractable

chemotherapy-induced nausea and vom-

iting in adults (which tends to persist with

optimized conventional antiemetic treat-

ment); CBD:THC spray for moderate or

severe spasticity in adults with multiple

sclerosis; and cannabidiol with a drug

called clobazam for seizures associated

with Lennox-Gastaut syndrome and Dra-

vet syndrome. There have also been a few

very small preliminary studies showing

benefits of smoked or vaporized marijuana

for easing noncancer (especially neuro-

pathic) pain. But these findings need con-

firming in larger follow-up trials.

If cancer patients are considering tak-

ing medical cannabis, they should first con-

sult their healthcare provider. However,

there are many approved, conventional

analgesics and other interventions that

are commonly used for controlling cancer

pain that have undergone clinical trials and

have been shown to be beneficial.

Based on existing evidence, there is

no role for cannabinoids in alleviating

cancer-related pain, and NICE does not

recommend cannabinoids for chronic

pain relief. Further research to under-

stand the effects/side-effects of different

cannabinoids or combinations of canna-

binoids is needed. g

Jason Boland is senior clinical lecturer

and honorary consultant in palliative

medicine at Hull York Medical School in

the UK. Follow him on Twitter @Jason-

WBoland. Elaine Boland is a consultant

in palliative medicine and honorary se-

nior lecturer at Hull University Teaching

Hospitals NHS Trust in the UK. Follow

her on Twitter @elaineboland17.

We could detect no difference between cannabinoids and

placebo in reducing pain scores across five high-quality studies.

CRITIC AT LARGE