Cannabis-based medicinal products, often shortened to CBMPs, have become increasingly visible in the treatment of persistent pain.

For some people they are presented as an exciting new option when conventional pain medicines have failed.

For others, the word “cannabis” immediately raises concerns about recreational drug use, dependence or safety.

As is often the case in pain medicine, the reality is more complicated than either position suggests.

CBMPs are legitimate prescription medicines that may be considered for selected patients. But they are not a cure for persistent pain, they are not suitable for everyone, and the scientific evidence supporting their use for chronic pain is still developing.

So where might they fit?

A relatively recent change in UK medicine

Although cannabis has been used medicinally in different cultures for centuries, cannabis-based medicinal products only became legally available for specialist prescription in the UK in November 2018.

The change followed a government review of the available evidence and recognition that some patients had significant unmet clinical need despite existing licensed treatments. Cannabis-based products for medicinal use were moved into Schedule 2 of the Misuse of Drugs Regulations, creating a legal route for specialist doctors to prescribe them when clinically appropriate.

This was an important change, but it did not mean that cannabis-based medicines suddenly became routine treatments.

NICE subsequently published specific guidance on cannabis-based medicinal products in 2019. The guidance considers their use in several areas of medicine, including chronic pain, spasticity in multiple sclerosis, severe treatment-resistant epilepsy and intractable nausea and vomiting associated with chemotherapy.

For chronic pain specifically, NICE does not currently recommend routine treatment with THC, THC/CBD combinations or related cannabis-based medicines, and recommends CBD only within a clinical trial. This reflects limitations in the quality of the available evidence and uncertainty about the balance of benefit, harm and cost at a population level.

However, UK legislation does allow specialist doctors to consider cannabis-based medicinal products for individual patients where clinically appropriate. In practice, this means they may be considered where there is a significant unmet clinical need — for example, when persistent symptoms remain troublesome despite appropriate conventional treatments, or when those treatments have caused unacceptable adverse effects.

This distinction is important.

Being legally prescribable does not mean a treatment is routinely recommended — but neither does the absence of a routine NICE recommendation mean that an individual patient can never benefit.

That is why careful patient selection, realistic treatment goals and ongoing review are particularly important when considering cannabis-based medicinal products.

What are cannabis-based medicinal products?

The cannabis plant contains many different chemical compounds, known as cannabinoids.

The two most familiar are tetrahydrocannabinol (THC) and cannabidiol (CBD).

THC has psychoactive effects and is responsible for many of the effects traditionally associated with recreational cannabis.

CBD does not produce the same intoxicating effect.

Prescription CBMPs can contain different proportions of THC and CBD and are available in different formulations.

Importantly, prescribed cannabis-based medicinal products are not the same thing as buying cannabis recreationally or purchasing CBD products from a health-food shop or online.

A prescribed CBMP is selected, prescribed and monitored as a medicine.

Why might cannabinoids affect pain?

Our bodies have an endocannabinoid system.

This is a naturally occurring signalling system involving cannabinoid receptors and internally produced cannabinoid molecules. It has roles in a number of physiological processes, including pain processing, sleep, appetite, memory and mood.

Cannabinoids from the cannabis plant can interact with this system.

This provides a plausible biological mechanism through which cannabis-based medicines might influence pain and some of the symptoms that accompany it.

But a plausible mechanism doesn't automatically mean that a treatment works well in clinical practice.

That requires good-quality evidence.

What does the evidence tell us?

This is where some caution is needed.

There have been clinical trials examining cannabinoids in different persistent pain conditions, including neuropathic pain.

Some people report meaningful improvements in pain, sleep or quality of life.

However, when results are examined across larger groups of patients, the overall benefits demonstrated in clinical trials have generally been modest, and the quality and consistency of the evidence varies.

We also have less information about the long-term benefits and harms of many CBMPs than we have for more established medicines.

For this reason, cannabis-based medicinal products are not currently recommended as routine treatment for chronic pain within NICE guidance.

That doesn't mean nobody can benefit from them.

It means the evidence isn't strong enough to say that they should routinely be offered to everyone with persistent pain.

Those are very different statements.

Evidence describes populations, not individuals

This is one of the recurring challenges in pain medicine.

Clinical trials tell us what happened on average to groups of people.

They cannot tell us with certainty what will happen to the individual sitting in front of us.

A treatment with a relatively modest average effect may still provide substantial benefit to a particular person.

Equally, a treatment that has helped somebody else enormously may do very little for you.

That is true of many treatments used in persistent pain, not only CBMPs.

The important question is therefore not simply:

“Does medical cannabis work for pain?”

A better question might be:

“For this particular person, with this particular pain problem, after considering what has already been tried, is a carefully monitored trial reasonable?”

They are not usually a first treatment

Persistent pain has many potential treatments.

Depending on the underlying problem, these might include physiotherapy and rehabilitation, conventional medication, targeted injections, psychological approaches, treatment of sleep problems, lifestyle changes or occasionally surgery.

Before considering a cannabis-based medicinal product, it is important to understand the pain as well as possible and review what has already been tried.

Sometimes that review reveals a more appropriate treatment that hasn't yet been explored.

CBMPs therefore generally sit later in the treatment pathway, rather than being the first thing we reach for.

What might improvement look like?

As with other pain medicines, I don't think the only useful outcome is a change in a numerical pain score.

If a CBMP is being used, we should be clear about what we are hoping it will achieve.

Perhaps pain becomes more manageable.

Perhaps sleep improves.

Someone may be able to walk further, exercise more comfortably or participate more effectively in rehabilitation.

Perhaps another medication that is causing troublesome side effects can eventually be reduced.

Or perhaps there is no meaningful improvement at all.

That last possibility matters.

A trial of treatment should be exactly that — a trial.

If a medicine isn't providing worthwhile benefit, continuing it indefinitely simply because it is called medicinal cannabis doesn't make sense.

What about replacing opioids?

CBMPs are sometimes promoted as an alternative to opioid medication.

It is an attractive idea, particularly given the difficulties associated with long-term opioid treatment.

But we need to be careful about making promises that the evidence doesn't yet support.

Some individual patients may find that successful treatment allows other medication to be reduced.

That can be a worthwhile outcome.

But cannabis-based medicines should not be presented as a guaranteed way of stopping opioids, and prescribed opioid medication should not simply be stopped when a CBMP is introduced.

Any reduction in long-term medication needs to be planned carefully and individually.

What are the side effects?

Cannabis-based medicines can cause side effects.

Depending on the product, dose and individual, these may include:

• dizziness

• drowsiness or fatigue

• changes in concentration and memory

• nausea or changes in appetite

• mood changes

• feelings of intoxication or being “high”

• anxiety or other psychological effects.

Cannabinoids can also interact with other medicines.

THC-containing products require particular consideration because of their psychoactive effects and potential effects on cognition, mental health and the ability to perform safety-critical activities.

As with any medicine, potential benefit needs to be balanced against potential harm.

Driving and everyday safety matter

This is particularly important with THC-containing medicines.

A medicine that affects alertness, coordination, reaction time or judgement can have implications for driving and other activities where impairment could be dangerous.

Patients prescribed CBMPs need clear advice about their particular medication, possible impairment and their responsibilities around driving.

The fact that something has been legally prescribed does not mean that it is safe to drive while impaired by it.

Cannabis-based medicine isn't right for everyone

There are circumstances in which CBMPs may be unsuitable or require particular caution.

A person's physical and mental health, other medication, previous experiences with cannabis or other substances, occupation, driving requirements and individual risk factors all need consideration.

This is one reason why prescribing should follow a proper medical assessment rather than simply matching a diagnosis to a product.

What about CBD you can buy yourself?

This is another area where terminology becomes confusing.

CBD oils and supplements available online or from shops are not the same as prescription cannabis-based medicinal products.

The dose, composition, quality control and evidence behind consumer CBD products can vary considerably.

“Natural” also doesn't automatically mean harmless.

CBD can interact with medicines and can have biological effects of its own.

If you are already taking CBD products, it is worth mentioning this when discussing your medication with your doctor.

Why is access through the NHS limited?

Cannabis-based medicinal products can legally be prescribed in the UK in appropriate circumstances, but access through the NHS for persistent pain remains very limited.

This is largely because the evidence for chronic pain has not yet demonstrated sufficient and consistent benefit to support routine NHS prescribing.

Private prescribing exists within a different funding context, but the scientific uncertainty doesn't disappear simply because treatment is being provided privately.

The same principles should apply:

Is there a reasonable clinical rationale?

Have appropriate alternatives been considered?

Is the treatment helping?

Are there significant adverse effects?

Does continuing it still make sense?

Neither miracle nor menace

Cannabis-based medicinal products are sometimes discussed at two unhelpful extremes.

At one extreme, they are presented as natural medicines that conventional healthcare has somehow failed to recognise.

At the other, they are dismissed simply because they originate from cannabis.

Neither position is particularly useful.

CBMPs are pharmacologically active medicines.

Like other medicines, they have potential benefits, limitations, interactions and adverse effects.

And like many treatments in persistent pain, the evidence is imperfect.

Where do CBMPs fit in good pain medicine?

For me, the important starting point is not the medicine.

It is the person.

What kind of pain are they experiencing?

What is contributing to it?

What treatments have already been tried?

What has helped?

What has caused problems?

What are they hoping to achieve?

And what are the reasonable options from here?

For some people, a cannabis-based medicinal product may eventually form part of that conversation.

For many others, another approach will make more sense.

The important thing is that CBMPs are considered with the same thoughtful clinical scrutiny we should apply to any other treatment for persistent pain.

Not because cannabis-based medicines are miraculous.

Not because they should be feared.

But because they are medicines — and medicines should be used when the likely benefits justify the risks.

Declaration of interests

Dr Charlotte Small is Chief Medical Officer of Leva Heal UK, a specialist medical cannabis clinic. This article is intended to provide balanced educational information about cannabis-based medicinal products and persistent pain. It is not intended to promote CBMP treatment or Leva Heal UK, and no commercial relationship exists between Leva Heal UK and Wye Sanctuary.