Chinese Medicine Demystified (Part V): How Acupuncture Relieves Pain
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Chinese Medicine Demystified (Part V): A Closer Look at How Acupuncture Relieves Pain


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Note: This is the fifth article in an ongoing series. If you haven’t read the first four, I recommend doing that before continuing:

In this article we’re going to take a closer look at one of the latest theories on how acupuncture relieves pain. I’m going to break it down in plain language for my readers who don’t have a scientific background, but I’ll also provide references at the end of the article for those of you that want the nitty-gritty detail.

Keep in mind that pain research is a constantly evolving topic, and more is being learned each year about the mechanisms of pain relief via acupuncture. (Although as an interesting side note, according to Professor Bruce Pomeranz of the University of Toronto, we know more about acupuncture analgesia than many chemical drugs in routine use. For example, we know little about the mechanisms of most anesthetic gases but still use them regularly. 1)

What I’m going to share with you here represents the latest information from the American Academy of Pain Management and papers published in major peer-reviewed journals.

The physiology of pain

Before I explain the mechanism, I have to give you a little background on the physiology and neurology involved.

There are two types of nerves involved in our perception of pain: sensory (nocioceptive) and position (proprioceptive) nerves. Both of these nerve types are firing at the same time in an area where we’re experiencing pain.

These nerves travel to the spine and pass their information on to neurons in the spinothalamic tract. This tract travels up the lateral dorsal horn of the spinal cord to the mid-brain.

The sensory nerves register pain. The position nerves tell the brain where that pain is coming from. So the sensory nerves say “ouch!” and the position nerves say “my knee!”.

There are two different types of sensory nerves involved in the acupuncture response. There are A-Delta fibers, which transmit sharp, burning pain messages. And there are C-fibers, which transmit dull, throbbing pain messages. A-Delta fibers are responsible for acute pain, and the signals they send are short-lived. They fire for a while and then the signals die off. C-fibers are responsible for chronic pain, and fire over an extended period of time.

A-Delta fibers are surrounded by a fatty, myelin sheath and the signals they send travel at 60 ft/second (that’s fast!). C-fibers are unmyelinated and their signals travel at 20 ft/second.

The A-Delta fibers mediate what is known as the “gamma loop”. The gamma loop is what gets activated when you stick your hand in a fire and your hand jumps back. These nerve fibers respond so quickly that your hand is immediately pulled back out of the fire. Chronic pain is a C-fiber problem, so C-fiber signals don’t travel quite this quickly.

Now, if the signal strength of the position nerves (the ones that register the location of pain) is what it’s supposed to be, the brain will release powerful natural pain relieving substances called enkephalins when it starts to receive those C-fiber messages. The enkephalins then plug up pain receptor sites in the brain, spine and capillary beds where the pain is located. This stops the pain in its tracks.

When things go wrong

Unfortunately, this is not what happens in people with chronic pain. Why? The current explanation is that the position nerve signal going up to the brain is too weak. The mid-brain can’t figure out where the pain is coming from, so the enkephalins don’t get released. This is why people in chronic pain often have trouble identifying exactly were the pain is. The neural threshold of the position nerve pathway is too low, so these people aren’t getting a clear signal where the pain is emanating from.

Because the brain isn’t getting the message, the nerves keep firing. And keep firing. After a while the nerves become inflamed, which in turn further weakens the signal’s ability to jump the threshold and get the message to the brain.

So that’s the first problem. The nerve signals are too weak and aren’t stimulating the brain to release the natural painkillers.

The second problem involves a survival mechanism that the brain evolved a very long time ago. Let’s take a knee injury as an example. When we bang our knee into something, the brain immediately takes measures to protect it. The brain doesn’t know what happened to the knee, but it assumes a worst-case scenario. Maybe you were bitten by a poisonous snake, or perhaps you seriously cut your knee and are losing a lot of blood.

What the brain does in this situation is restrict the blood supply going into the knee and the blood return coming out of the knee. This is actually a very intelligent choice. If you were bitten by a venomous snake, reducing blood flow around the knee will lessen the chance that the poison will spread. And if you were cut badly, reducing the blood flow will lessen your chances of bleeding to death.

This phenomenon is known as “guarding”. One of the results of reducing blood flow to the knee is that it becomes stiff and weak (sound familiar?). The brain wants it to feel weak because it is attempting to protect the knee. The brain doesn’t want whatever happened to the knee to threaten your chances for survival. So the brain sacrifices the health of the knee in order to keep you alive.

This was a great strategy before the advent of western emergency medicine. Almost everyone would prefer to lose function in their knee to death. But this isn’t a choice most of us have to make anymore, because when we cut our knee or get bitten by a snake we can go to the hospital and they can save our lives. And the problem is that cutting off blood flow to the knee – while it may have saved our lives in times past – dramatically limits the knee’s ability to heal.

Why? Because everything we need to heal is in the blood.

The blood contains analgesics (painkillers), anti-inflammatories, nutrients absorbed from food, oxygen, hormones and immune substances to fight infection. If the blood flow is restricted to a particular area, healing won’t occur. No blood flow, no healing.

Stop and think about this for a minute. It’s such an obvious fact that it’s often overlooked in medicine. It’s not taught in such a direct way in medical school, but when I’ve explained it to a couple of doctors they both said something to the effect of, “Huh. I never thought of it that way, but it makes perfect sense.”

How acupuncture helps

Okay, now we’re finally coming to the part where I explain how acupuncture fits into this picture. Inserting needles into the skin at peripheral sites “jumps” the neural threshold on the position nerve pathway, so that the signal can reach the brain. Once the signal reaches the brain, the whole series of events I described in the paragraphs above kicks in. The brain recognizes there is pain and where it’s coming from and releases enkephalins (painkillers).

This initial response is very fast. It should be perceived as almost instantaneous by the patient. But after the needling therapy the patient goes home and the pain comes back. The old bad habit of the nerve chronically firing below the threshold re-establishes itself. The body, just like the mind, has a hard time breaking bad habits.

But if the patient returns in a couple of days to get another treatment, the neural threshold will be jumped again. And if you keep jumping the neural threshold, eventually the central and peripheral nervous system figure out that it’s better to operate in the non-pain state than in the pain state. The technical term for this is re-establishment of neurological homeostasis.

Once this happens, the brain is no longer receiving pain signals from the knee. It no longer thinks the knee is injured or threatening the survival of the body. Now, instead of restricting blood flow to the knee, the brain does the opposite. It immediately vasodilates the capillaries and venules around the knee, which increases blood flow and begins the healing process.

What I’ve described above is how acupuncture relieves pain via the peripheral and central nervous system. There’s another pain relief mechanism that involves activating the immune system. Acupuncture needles are seen as foreign invaders to our body. Inserting a needle into the skin creates a micro-trauma that in turn stimulates the activity of immune cells that control inflammation.

There are millions of immune cells called mast cells in the dermis of the skin. These cells are like water balloons full of fatty molecules called leukotrienes and prostaglandins A & B. When a needle is inserted into the skin, it pops the mast cells and releases the leukotrienes and prostaglandins. Prostaglandins cause the cutaneous nerve in the area to fire (which activates the process described in the previous paragraphs). Leukotrienes are the strongest anti-inflammatory substance the body can produce.

Leukotrienes cause local capillaries to vasodilate and become permeable. White blood cells called macrophages leak out through the capillaries and immediately begin to heal the damage caused by the needle stick.

However, the healing caused by the needle insertion isn’t limited to the damage caused by the needle. If there is other damage in the area from previous traumas or injuries, that will also be addressed by the immune chemicals released by the needle insertion.

What’s more, the micro-trauma caused by the needle starts a systemic immune response. This promotes healing of the soft tissue throughout the body – not just at the needling site. After the needles are removed, the needle-induced lesions continue to stimulate the body until the lesions heal.

This means that the anti-inflammatory effect of acupuncture persists for 2-3 days (and sometimes as long as a week) after the needle is withdrawn.


Genetically the body is not designed to be in chronic pain. It will do everything it can to get us out of pain. Acupuncture “reminds” the body how it should be functioning, and helps its powerful inbuilt pain relieving mechanisms kick into gear. It’s a bit like jump starting a car. You’re not changing how the car works, or even adding anything to the engine. You’re just giving the battery a little jolt so the car can run how it’s supposed to.

It’s important to understand that this neurochemical mechanism not only provides pain relief, but also promotes homeostasis and tissue healing and regulates the immune, endocrine, cardiovascular and digestive systems. This explains why getting acupuncture treatment for your knee pain also addresses other problems you might have, such as asthma, irritable bowel, high blood pressure, anxiety and insomnia.

In the next and final article of this series, I’ll explain the advantages of Chinese medicine over western medicine for the prevention and treatment of most common health conditions.

Recommended resources for more information

  1. Pomeranz B. Acupuncture analgesia – basic research. In Stux G, Hammerschlag R, editors: Clinical acupuncture scientific basis. Berlin 2001. Springer.
  1. Jesse, one of my teachers have said, ‘When we examine any system of human medicine, we must first ask the question: “According to this medicine, what is a human being?” and, therefore, “What is a healthy human being?”‘ (Liu Ming)
    As Chris said very well in the Part VI article, western medicine mainly geared towards suppressing symptoms. This is the basis of how most researches are designed. For example, there are many clinical trials that follow the same logic: i.e. In a clinical trial, ___% of patients with (_____symptom) who undergo (______treatment, can be a drug, or surgery etc.) show improvement of symptom  compare to ___% who took placebo, compare to the control group…. The basic premise of most clinical trials of this kind is to see statistically how certain symptom is managed with a drug. However, are we just a statistical number? These research methodologies also play down the human factor to try to be “objective” about the results. However, we have to ask, between the drug and the symptom, where is the human being in it? 
    What does that say about the philosophy of western medicine? 
    Chris, I agree with you that chinese medicine has to be subject to scrutiny. But, as you know, Chinese medicine address the whole person, it considers the full range of human experiences (e.g. emotions, lifestyle, diet, climate and other environment factors) that leads to a systemic malfunction/imbalance to that leads to the symptoms. This paradigm is different from western medicine and so chinese medicine should be scrutinized under a different set of research methodology. 
    well said. as they say, “The difference between a medicinal and a poison is dosing.”

  2. Philip,

    I’m going to leave those posts to you!  It’s time for me to move on to other topics. Thanks again for your participation in this series!  I’ve enjoyed our dialogue a lot.

  3. Donna,

    I couldn’t agree more with your point, and that’s why I have a blog that challenges mainstream myths on nutrition and health.  But as Philip pointed out, it’s important to subject Chinese medicine to the same scrutiny.  Otherwise we’re just as guilty of what Ratcliffe is referring to.

  4. Jesse: Thank you for your open-mindedness.  I agree with almost everything you said.  Here are the exceptions:
    Yes, western medicine in theory (thank you for pointing that out) is based on science.  However, I would like to point out that so is Chinese medicine.  It is based on evidence – collective experience by practitioners accumulated over millenia – which I’m sure was subjected to the basic rigors of the so-called “scientific method”.  Namely – identify the problem, search for past attempts to solve the problem in the literature, formulate a hypothesis, experiment to prove or disprove the hypothesis, and draw conclusions.  Time has proven that some formulas or point combinations have faded away to obscurity because they don’t work as well as others.
    Secondly, science is only now validating what was known before.  I could fill this comment box with citation after citation concerning the effects of individual chinese herbs – both beneficial and otherwise.  It is difficult to analyze individual components of formulas, but formulas have been studied.  I just gave a lecture last week on scientific studies involving Liu Wei DiHuang Wan (Six Flavor Rehmannia Decoction) where it’s anti diabetic and immune modulating activity is proven through published studies.
    Thank you also for acknowledging that ALL science and ALL medicine have problems.  True, even chinese medicine is the victim of commercialization and money-making chicanery.  I’ve seen patients get kidney failure from overdosing on korean red ginseng, for example.  This was promoted by unscrupulous traders as a panacea… and being “natural” it supposedly had no side effects – forgetting the fact that a very “hot” herb like red ginseng should be used sparingly in a hot humid climate like in my Philippines.
    Donna is correct in that many people trust “scientists” implicitly because we are taught that science is an objective search for truth.  The truth is that modern science is an objective search for funding.
    Chris – I think one of the main problems with reconciling TCM and mainstream western medicine is the seeming inability to reconcile terminology.  It is my adamant belief that TCM will be easier to understand if the TCM philosophy and terminology is explained using the western paradigms – you got the ball rolling with your posts on the meridians.  Are you planning any more?  For example, we know fire = inflammation, what about damp?  or cold? =)

  5. Most of us have been taught that western medicine is based on science, and science represents the unbiased, objective way to search for truth. However, subjective judgments lie behind all the facets of “scientific” research. (Not to mention that nowadays, most clinical research are funded by pharmaceutical companies) 
    All data are theory-, method-, and measurement-dependent. That is, “facts” are determined by the theories and methods that generate their collection; indeed, theories and methods create the facts. 
    This means that how the problem will be defined, which model(s) of inquiry will be considered to be relevant to the problem as defined, which model(s) of inquiry will be considered to be relevant to the problem as defined, where one shall look (and, by implication where on shall not look) for evidence–and even what one shall consider to be constitutive of evidence–are all determined by the paradigmatic “map” or world view to which the scientist is committed. 
    –John Ratcliffe, Notions of validity in qualitative research methodology

  6. On one level I agree, Philip. Doctors can be wrong: their information can be outdated, and their understanding can be a misinterpretation. It is often good to get more than one opinion on an issue of diagnosis/treatment and try to find a consensus.
    On another level, I think “western” medicine is based on science, at least in theory (perhaps not in practice, with every doctor), and I believe the scientific method is a great way to avoid human error. It is not without problems of its own, of course, so here too there is value in seeking a consensus of people who have made a career of looking at the evidence. A few may be fooled by false conclusions, but it seems like the truth should be found by the majority. So it doesn’t surprise me much that people who cannot investigate matters well on their own should put their trust in the mainstream. Does that make sense?

  7. In life there are several ways to enter into belief.  One is through personal experience.  One is through gathering evidence and trying to fit the pieces together, like what we’re trying to do now.  Another is faith.  It’s too bad that there’s no level playing field when it comes to faith in medicine.  Because “western” medicine apparently predominates, “they” say something and people are more than likely to readily believe.  With Chinese medicine, from the point of view of an outsider, we usually demand a bit more, like what we’re doing now.  There’s a double standard though – people are more likely to accept western medicine “pronouncements” on faith alone (faith in medical authority).

  8. Oh, ok. I’ve learned some about the immune system, but it has mostly been in relation to its interaction with pathogens. It seems like my limited knowledge is getting in the way of my understanding more than ignorance would 🙂

  9. Yes, Philip.  The literature suggests that response to needling-induced tissue damage involves Th1 (cell-mediated) immunity, whereas the response to a vaccination involves Th2 (humoral) immunity.

  10. Acupuncture creates an inflammatory response – so the immune cells at work would be macrophages.  Vaccines work by forcing T-cells to go to work.  (If I recall my second year pathology right)

  11. Oh, it would be silly to use vaccines to stimulate the nervous system. I was just wondering whether vaccines might incidentally have the same effect as the acupuncture needles, if they both stimulate the immune system.

    • The mechanisms of acupuncture are similar in some regards to vaccination, but very different in other regards. I don’t think they can be considered in the same category.

  12. Hypodermic needles are not retained for any significant length of time.  Getting vaccine injections just to stimulate a peripheral nervous system response is certainly overkill. Not to mention the side effects and risks of injecting a modified live virus into the body, which are well documented.

  13. Okay. So, if stimulating the immune system with a needle leads to healing throughout the body, something like vaccines should be even better for that, right? Or any kind of injection, to some extent.

  14. It’s not exactly damage… it’s more of a controlled stimulation.  Pomeranz’s studies show that it is the A-delta fibers which are stimulated and give off the “qi” sensation.  Naloxone blocks this effect and blocks the pain control.

  15. Ok, so it’s the type of damage which elicits a certain pain response that induces painkiller release, rather than the amount of the certain type of pain or something? I get it.

  16. Question for you: why do you suspect that longer-term pain relief is due to placebo?  What leads you to that conclusion?
    My answers to your questions:
    1) Unfortunately the reference I have for that is Donald Kendall’s book, and a 8-hour seminar I did with him last weekend.  The information about involvement of proprioceptive fibers in the needling response came from a lecture by Robert Doane, who is an acupuncturist and also a member of the American Academy of Pain Management.  Some of this work hasn’t been published yet, as far as I know, but let me try to explain further.
    My understanding is that propagated sensations induced by afferent nocioceptive fibers triggered by needling are mediated by afferent proprioceptive fibers and propriospinal neural reflexes.  Nocioceptive fibers activate propriospinal fibers to produce muscle flexion responses.  Proprioceptive group II afferents send terminal branches to all laminae except II, and ultimately synapse on motor fibers.  Propriospinal short and long fibers traverse the length of the DLF.
    Somatic and visceral nocioceptive fibers and proprioceptive fibers trigger dorsal root potentials and reflexes (DRR).  These reflect up and down the DLF, firing nerves above and below entry level signal.  These nerves may have a role mediating afferent inputs and supraspinal descending control (which I discussed in the article).
    2) Mast cells do release histamines, and leukotrienes can have inflammatory and anti-inflammatory effects.  What I didn’t make clear in this article due to length considerations is that tissue reactions to needling-induced micro-trauma follow a set order.  The initial response is to mount a strong defensive (inflammatory) reaction.  This is important to keep blood clots from forming so immune cells can flow in.  But all needling induced inflammatory reactants are neutralized in the final phase.
    Vasodilatory, nocioceptive nerve excitation and chemotactic, solubility activities predominate during the initial phases of needling response.  Tissue repair and inactivation of reactants predominate during intermediate and latter phases of reaction.
    3) I am not sure of the exact mechanism, but many studies show that muscular ischemia is a defining characteristic of chronic pain.  Maintenance of sympathetic vasoconstriction of peripheral tissues over time results in ischemia, inflammation and pain.  See this paper for more info.
    I’ve often heard the claim that “little is known about the analgesic effects of acupuncture.” On the contrary, according to Professor Bruce Pomeranz of the University of Toronoto, “We know more about acupuncture analgesia than about many chemical drugs in routine use. For example, we know very little about the mechanisms of most anesthetic gases, but still use them regularly.” (There are of course countless drugs and entire classes of drugs we don’t understand the mechanisms of action for, including aspirin.)
    Moffet’s recent review in the Journal of Clinical Epidemiology demonstrates that acupuncture is distinguishable from placebo and affects outcomes. What is less clear in the literature is whether point selection and technique make a difference in outcomes.

  17. Hello, I am skeptical of acupuncture (and homeopathy, and chiropractic, and most other alternative medicine), but would like to ask a few questions so I can at least understand it better – even if I still may not accept its validity! I do recognize its benefit in short-term pain relief through gate control, but suspect longer-term pain relief is due to placebo instead of physiological changes.
    First, do you have a reference for the role of proprioceptors in pain perception? My understanding is that proprioceptors act to inform us of our body position, not pain perception. Pain position is reported by the same nerves as report the pain itself.
    Don’t mast cells also release histamines, which trigger an inflammatory response? According to your description of action (and according to Wikipedia leukotrienes are also an inflammatory agent, not an anti-inflammatory.
    You say that the body has a long-term response to injury of reducing blood flow to the area. It was my understanding that the vasoconstriction in response to injury was very short-term, around ten minutes, followed by vasodilation.Is there another mechanism for longer-term vasoconstriction to a wound? The texts I have available don’t mention one, but they are rather introductory.
    I apologize if your references address any of these – I’m a broke college student, so don’t want to spend money on more books!

  18. Hi Jesse,

    The mechanism is as I described it in the article.  Any penetration of the skin, whether it is perceived as painful for not, will trigger the body’s defense mechanism and stimulate the PNS.  This leads to the cascade of analgesic and anti-inflammatory responses I described.