"Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in such terms." - International Association for the Study of Pain
Pain is often considered man's worst enemy, even more so than death itself. The science behind pain should be known so that we can treat it.

Simply put, when a painful stimulus is given, nociceptors or the pain receptors in the skin or tissues are stimulated. They then send impulses along the axons of the sensory neurons into the spinal cord. From there, another neuron relays this signal to the brain. Before it reaches the brain, this pain sensation is sent to the thalamus for processing. Then the processed information goes to the sensory cortex of the brain and you feel pain. This is a very concise version of how you will feel pain. This pathway is called the ascending pain pathway. There are also descending pathways that change how you feel pain. The actual process is much more complex and involves many theories and is important in modulating pain and relieving it.

There are many types of pain. Acute pain is what is felt suddenly. For example, it is felt when you prick your thumb with a needle.

Chronic pain is felt over a longer period of time. This is important because chronic pain causes the pain process to take on a life of its own. Analgesic abuse is common in this population. These patients are often given a lot of prescription drugs, including opioid drugs. Over time, they become addicted to these medications and it becomes difficult to get off of them.

Prescription opioid abuse

In recent years, opioid abuse has become a major problem in the United States and around the world. According to a 2003 epidemiological study, opioid painkillers were among the most commonly abused drugs among secondary school students. Alarmingly, the use of opioid medications has increased more than ever before. This has paved the way for addiction and major social problems.

Long-term use of prescription opioid medications has been linked to addiction or abuse in 2.8-18.9% of patients, according to research. This is why we need effective alternative methods of pain relief.

How does hydrogen relieve pain?

Molecular hydrogen has many amazing properties that make it a useful medical therapy for many diseases. Scientists are currently researching its use in these diseases. One of the most well-known effects of hydrogen, even before it was officially recognised, was its ability to relieve pain. This is a very useful property and may be used in the future, especially by chronic pain patients, to alleviate their suffering.

There are many studies on this pain-relieving property of hydrogen. Let's take a look at some of them to better understand the mechanisms behind it. Molecular hydrogen has anti-inflammatory, anti-apoptotic and antioxidant effects, among others. Therefore, scientists thought that hydrogen could relieve pain involving many cytokines and other inflammatory mediators. It is known that reactive oxygen and nitrogen species are key molecules that mediate pain.

In a study by Chen et al. in 2015, neuropathic pain was induced in a group of rats. Neuropathic pain is caused by injury to nerves and is an excruciating and persistent pain that is difficult to treat. When the rats were injected with molecular hydrogen into the peritoneum twice a day, the pain was tested by the release of inflammatory cytokines. They found that hydrogen could inhibit neuropathic pain by reducing hyperalgesia, or hypersensitivity to pain. Hydrogen increased the so-called HO-1 mRNA and specific protein expression. It improved the activities in the process of pain. The scientists suggested that in addition to the anti-inflammatory effect, there is also an anti-nociceptive effect for hydrogen.

In another study, hydrogen-rich saline was administered intracutaneously to neuropathic pain induced by L5 spinal nerve ligation in a rat model. The results were promising. The researchers found that hydrogen reversed the overexpression of MnSOD (a type of dismutase enzyme) by tyrosine nitration. They also found that the analgesic effect of hydrogen-rich normal saline was associated with decreased activation of astrocytes and microglia (special nerve cells) triggered by overproduction of hydroxyl and peroxynitrite. There was also decreased expression of interleukin-1β (IL-1β) and tumour necrosis factor-α (TNF-α) in the spinal cord. Ge, Y., et al. hypothesised that the antioxidant property of hydrogen can be used as an analgesic.

Conclusion
Since the therapeutic effect of hydrogen has only recently been discovered, its efficacy is still being researched. Although it has only been tested on rat models so far, many people have already ingested molecular hydrogen. There are many testimonials about how hydrogen has relieved various chronic pains. Hydrogen is very important as it could be the next best painkiller as it has no known side effects at recommended doses. Hydrogen has a promising future in defeating the culture of opioid abuse and leading to effective, simple methods of pain relief without addictions.

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