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. Oh no! It was going so well! I was going to forward this to my colleagues, but then you made some errors, and as we know, small errors make people suspicious and likely to ignore big truths. Leukotreines are PRO-inflammatory. The process you described of white cell recruitment and margination is one of the steps of inflammation. In fact, everything you described, is actually inflammation. The increased vasodilation and permeability of the capillaries is what gives us the heat and swelling of inflammation. The swelling and release of white cell inflammatory markers stimulate merkel cells to release pain signals via their synaptic connection to dermal afferent nerves. The increased metabolic activity of immune cells and their released chemicals of recruitment also contribute to the heat associated with inflammation. That’s ok though, because what you have said is true, the process of inflammation is actually the body’s repair system, the recruitment of macrophages and neutrophils to phagocytose invading organisms and damaged cells, the increased blood flow to provide metabolic components to fuel rapid tissue repair. When it’s working well, it’s a good thing. My undergraduate degree was in Acupuncture, and I’m currently doing graduate-entry Medicine/Surgery. What you have said makes a lot of sense and I have really enjoyed the series.

  2. Well, ok, but why can needling LI 11 take away knee pain (especially at Liv 8, St 35 and K 10)? Why can needling K3 on one side and Bl 65 on the other effectively relieve back pain along the whole Bl channel (if I’m allowed that terminology). Can you really explain that without using the concept of the channels?

  3. “Leukotrienes are the strongest ANTI-inflammatory substance the body can produce.”

    Leukotrienes are NOT ANTI-inflammatory molecules, they are PRO-inflammatory molecules and a necessary part of the immune response.

  4. (slight fix in the quoted HTML)
    I’m using Firefox 3.6.3 in WinXP + SP3.
    BTW, your comment, sent to me in gmail, had all the HTML code exposed, not rendered. Like so (I’ve changed the angles to square brackets):
    Author: Chris Kresser
    [p]The list works fine for me:[/p]
    [li]a [/li]
    [div]As does the [span style=”text-decoration: underline;”]underline[/span] and [span style=”text-decoration: line-through;”]strikeout[/span].[/div]
    [div]What platform are you using?[/div]
    Oh, I hate this sort of thing, and it happens all the time. Not just to me, I mean.

  5. I’m using Firefox 3.6.3 in WinXP + SP3.
    BTW, your comment, sent to me in gmail, had all the HTML code exposed, not rendered. Like so (I’ve changed the angles to square brackets):
    Author: Chris Kresser
    [p]The list works fine for me:[/p]
    [li]a [/li]
    [div]As does the [span style=”text-decoration: underline;”]underline[/spanand [span style=”text-decoration: line-through;”]strikeout[/span].[/div]
    [div]What platform are you using?[/div]
    Oh, I hate this sort of thing, and it happens all the time. Not just to me, I mean.

  6. The list works fine for me:

    1. This
    2. is
    3. a
    4. test.
    As does the underline and strikeout.
    What platform are you using?

  7. BTW,

    why does this comment form have icons for lists if they don’t make lists?
    And let’s test the

    underline, and
    strikeout icons as well.

  8. Slow down a bit there,  Skeptic, your typing fingers are running on ahead of your brain, or else you edited too fast. I’d bet dollars to donuts that you’re confusing nerves with nerve signals, in your text if not in your mind. Quoting you:

    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 are short-lived. They fire for a while and then die off. C-fibers are responsible for chronic pain, and fire over an extended period of time.

    Do you really mean that an A-Delta fiber is short-lived and dies soon after it transmits a pain signal? It seems much more likely that the signal carried by an A-Delta fiber is short-lived and dies off quickly.
    Similarly, immediately after that:

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

    Damn, how do either of them stay in our bodies? Again, it’s the signals that travel at these rates, not the nerves that carry them. The nerves are the tracks, the signal is the train.
    I’ve been reading this article with interest, but now your carelessness is making me cautious.

    • Mark,

      I meant to describe the signals sent by those fibers, not the fibers themselves. Thanks for catching the mistake.

  9. “RCTs have no way of controlling for these variables and they don’t even try to.”

    What is the randomization for, then? If the sample size is large enough, it should work out that there are about the same number of people who eat well, exercise, and get sleep, so if the acupuncture works, those people should be affected by it enough to distinguish it from the controls. Right?

  10. I disagree, Matto: placebo acupuncture is not easy to do, at least not in a blinded manner. The person giving the treatment can easily tell whether the needles they are using are puncturing the skin or not, assuming they’re using the fake needles. Still, it seems like that should increase the apparent efficacy of the real acupuncture, if anything, so studies that show that it is no better than placebo might still be worth something… of course, it is claimed that even poking people with toothpicks is still real acupuncture.

  11. If Acupuncture can treat or cure any given illness, then this is easily prove-able. At some point along the timeline, a given practitioner or group of practitioners will be able to isolate who has said condition and design a placebo controlled study. This has already been done. As placebo acupuncture is easy to do. There has never been a successful study like this that can be replicated. There have been many attempts, including the famous post partem depression studies and many many others. It has proven so completely impossible to demonstrate acupuncture’s effectiveness , that it is quite hard to get acupuncturists to participate these days. You can find many studies that seem to show the effectiveness of Acupuncture vs placebo Acupuncture, but if you look deeper, you will find many cases where the study was repeated by others and failed repeatedly. I did extensive research on the topic, originally hoping to find the opposite result. Don’t kill the messenger, I am truly just stating the facts of the matter, you can see for yourself.

    • Matto,

      Thanks for your comment.

      Acupuncture has the potential to treat or cure any illness. But this is only true insofar as the human body has that potential, since acupuncture works by stimulating innate healing mechanisms. This means that acupuncture’s ability to treat or cure illness is dependent upon the status of the person being treated. If their self-repair mechanisms are significantly damaged in some way, acupuncture will not be able to address their condition.

      For this same reason (and several others), acupuncture research is difficult. Healing never takes place in a vacuum. If two study subjects receive the same acupuncture treatment, but one is eating well, exercising, and getting plenty of sleep, while the other is eating junk, not exercising at all, and sleeping 4-5 hours a night, who do you think will improve? RCTs have no way of controlling for these variables and they don’t even try to. This highlights the fundamental difference, once again, between holistic and allopathic medicine. In holistic medicine we consider not only the physiological functioning of the entire body, but also the effects environmental factors, nutrition, exercise, stress, emotional and psychological state, etc. In allopathy, the focus is usually on chemically altering the function of one part of the body without regard to the influence of the rest of the body or the other factors I just mentioned.

      What I’m suggesting is that together with an appropriate diet, stress management, exercise, and other aspects of a healthy lifestyle, acupuncture makes far more sense as a preventative care modality and a means to address mild to moderate imbalances than surgery and drugs.

    • Matto,

      I forgot to mention, a new study was just published that addresses your question directly and reaches a different conclusion. From the abstract:

      We reviewed the available literature for different placebos (sham procedures) used to control the acupuncture effects, for moderators and potential biases in respective clinical trials, and for central and peripheral mechanisms involved that would allow differentiation of placebo effects from acupuncture and sham acupuncture effects. While the evidence is still limited, it seems that biological differences exist between a placebo response, e.g. in placebo analgesia, and analgesic response during acupunture that does not occur with sham acupuncture. It seems advisable that clinical trials should include potential biomarkers of acupuncture, e.g. measures of the autonomic nervous system function to verify that acupuncture and sham acupuncture are different despite similar clinical effects.

      After reviewing the available literature, these authors did find a biological difference between acupuncture and sham acupuncture. I think the jury is still out on this question.

  12. Again, Chris and I would differ in opinion on this one.  I’d have to get my copy of Huangdi Neijing and Zhenjiu Jiayijing to be sure though..
    What I’d like to say though, is that there should be many ways of looking at the same thing, in order to achieve a better understanding.  (just not the “energy meridian”… )

    • Who knows? There may be a correlation. But as I explained in the second article of the series, I think the ancient Chinese were referring to blood vessels. Keep in mind that the word “meridian” and their particular arrangement on the body was an invention of Soulie de Morant in the early 1900s. The meridians as we know them today aren’t found in classic Chinese texts.

  13. Okay, that’s what I thought you were saying. Thanks for answering my questions. At this point it sounds like I would prefer toothpick treatment if I were ever to get acupuncture, as it sounds more pleasant, though I’m sure your experience suggests that it wouldn’t work as well, hehe.

  14. Jesse, you’re combining two mechanisms into one.  The first involves stimulating the peripheral nervous system to “jump” the neural threshold so the brain will begin releasing painkillers.  The second involves the local inflammatory response that occurs when a needle punctures the skin.  We might expect actual needling to provoke a stronger response in the second case, but in the first it’s possible that a toothpick pressed against the skin may have a similar effect.

  15. Jesse, actually just touching your skin against something causes capillaries to burst.  It’s just that our bodies are quite efficient in immediately repairing the damage.  If not, we’d have bruises all over.

  16. So toothpicks induce A-Delta fiber firing without penetrating the skin? If I read the original post correctly, that was one of the two mechanisms you proposed for how acupuncture works: Needling causes micro-traumas that induce the brain to release painkillers and allow the old injury to heal. Do toothpicks cause micro-traumas?