Pain is something everyone experiences at some point, from the sharp pain of a kicked toe to the dull ache of a sore muscle.  But did you know that there are four discrete causes of pain? 

Clinical Academic Pharmacist and HMRI Heart and Stroke researcher, Professor Beata Bajorek, says, “The type of pain being experienced depends on which body system – nervous system, immune system – (not necessarily body part) has been ‘harmed’.

“When it comes to types of pain, we broadly refer to nociceptive pain which may include inflammatory and non-inflammatory pain, neuropathic pain, and nociplastic pain,” she says.

Nociceptive pain 

Nociceptive pain usually involves direct injury or illness to a part of the body.

“The ‘noci’ is a latin term for ‘to do harm’, which recognises that pain is often a symptom of some harm having been caused to the body or body processes, for example, through injury or illness,” says Professor Bajorek.

“When our tissues detect any injury, various physiological processes are activated to alert us to the injury so that we do something about it and protect ourselves. This is the purpose of pain. These processes then kick into gear to try and naturally fix the problem.

“This involves our tissue fibres and nerve endings (nociceptors) sending signals throughout our body and to the brain, and the body producing molecules that trigger inflammation such as cytokines, chemokines and nerve growth factors. Inflammation is what our immune system does to further protect the body and prevent complications such as infection from bacteria and viruses at the site of injury,” she says.

Neuroceptive pain 

‘Neuro’ refers to ‘neurological’. This is pain that originates from our nervous system, where some type of injury or illness has affected the nerves throughout our body.

Professor Bajorek explains that a person may experience a physical injury where the nerves are damaged or they may experience an internal illness that damages the nerves or changes how the nerves send signals through the body.

“In older people, the shingles virus (varicella zoster virus or Herpes Zoster) can be reactivated in the nerves, interfering with nerve signals and sometimes damaging the nerves, leading to a painful condition called post-herpetic neuralgia. In neuropathic pain, the damaged nerves keep sending pain signals to different parts of the body, sometimes even after the injury itself has been repaired,” she says.

Nociplastic pain 

Nociplastic pain is a bit different in that it may occur even without a specific injury.

“It’s a dysfunctional but real pain that appears to serve no purpose or protection. It’s thought that there are faults in the body’s messaging systems, leading to pain signals being sent when there is no specific pain trigger. Fibromyalgia is a common example of nociplastic pain,” says Professor Bajorek.

Psychogenic pain 

A fourth category of pain is psychogenic pain which is usually caused by an underlying mental health condition (emotional stress, anxiety, depression). Common examples include simple headaches due to stress or anxiety, non-injurious muscle or stomach pain.

What pain reliever should you use for different kinds of pain?

Painkillers don’t treat the cause of the pain – they treat the symptoms – and not all painkillers will work for all kinds of pain.  

Clinical Academic Pharmacist and Heart and Stroke researcher, Professor Beata Bajorek, explains, “Analgesic medications (painkillers) reduce the sensation of pain by turning off the body’s systems that produce the molecules that cause pain or they change how the tissue fibres and nerves send out pain signals.”

There are three factors that determine which painkiller to use. They are:

1. The type of pain 

Professor Bajorek says, “For nociceptive pain (pain caused by direct injury or illness), ‘simple’ general-purpose analgesics such as paracetamol or aspirin are a good starting point.

If the treatment doesn’t work, then the ‘analgesic ladder’ comes into play.

“In this ‘ladder’ approach, we work our way from lower dose simple pain relievers up to more specific or more potent analgesic combinations to ensure we get the right medicine in the right dose for each person.

“If a simple analgesic isn’t enough, we might swap to a more specific anti-inflammatory agent if inflammation is present, for example, non-steroidal anti-inflammatory drugs (NSAIDs). Or we may add a small dose of an NSAID (e.g. ibuprofen) to paracetamol.

“If it’s not inflammatory pain, then a mild opioid analgesic at a low dose (e.g. codeine) might be added to paracetamol.

“If the pain is neuropathic, we might add an agent that specifically works on the nervous system – this includes agents that are also used in conditions such as in epilepsy (e.g. gapapentin, pregabalin, carbamazepine, valproate) or anxiety and depression (e.g. amitriptyline , imipramine, nortriptyline). For muscular pain or cramps, a muscle relaxant might be added instead.

“If more pain relief is needed, we might step up the ladder and consider using some of the moderate potency opioid or opioid-like pain relievers (e.g. tramadol) at lower doses before increasing doses.

“For more severe pain, we might consider using the more potent opioid analgesics (e.g. morphine).

“There are a number of very different agents that we can use in treating different types of pain. The key is to assess the pain well from the start,” says Professor Bajorek.

2. The severity and duration of the pain 

Professor Bajorek says, “For mild pain, we would use simple pain relievers like paracetamol. For mild to moderate pain, we might consider using specific anti-inflammatory agents like aspirin or non-steroidal anti-inflammatory drugs.

“For moderate to severe pain, we might use more potent pain relievers, choosing different medications depending on the type of pain, such as stronger anti-inflammatory agents, selected opioid or opioid-like medications, or neurological agents.

“For really severe pain, we would look at more potent alternatives within these medication classes, as well as look at what we call adjuvant analgesics – other types of agents that may help block pain like anesthetics,” she says,

3. The location and size of the pain  

Not all pain requires oral pain relievers. If the pain is limited to a small area or specific part of the body, topical pain relievers may be considered.

Professor Bajorek says, “Where the pain is in a larger area or more widespread throughout the body, then we need to give pain relievers in a way that reaches multiple areas via the bloodstream. This is usually done with orally administered medicines, but sometimes we use injections, patches and suppositories.

“For a person who has arthritis pain, a topical anti-inflammatory ointment might be enough for pain that is limited to just the fingers of one hand but if the person was experiencing arthritis pain in multiple joints it would be appropriate to use an oral anti-inflammatory medicine. However, if the person was experiencing nausea after taking medicine orally, we could consider using a patch or a suppository.

“Many medicines come in multiple formulations so that we can tailor the treatment to the needs and preferences of the patient,” she says.