Pain is a sensation that is transmitted from an area of tissue damage or stress along the sensory nerves to the brain. The brain interprets the information as the sensation of pain.
Substances that decrease pain either interfere with the ability of nerves to conduct messages, or alter the brain’s capacity to receive sensations.
Pain may be a symptom of an underlying pathological condition, such as inflammation. It may also be due to other causes, such as bruising, infection, burns, headaches, and sprains and strains. Use caution when treating pain without understanding its cause—this may delay diagnosis of conditions that could continue to worsen without medical attention.
What are the symptoms of pain?
Symptoms of pain include discomfort that is often worsened by movement or pressure and may be associated with irritability, problems sleeping, and fatigue. People with pain may have uncomfortable sensations described as burning, sharp, stabbing, aching, throbbing, tingling, shooting, dull, heavy, and tight.
Lifestyle changes that may be helpful for pain
Body weight may be related to pain tolerance. One study indicated women who are more than 30% above the ideal weight for their age experience pain more quickly and more intensely than do women of ideal weight.1 No research has investigated the effect of weight loss on pain tolerance.
Exercise increases pain tolerance in some situations,2 3 in part because exercise may raise levels of naturally occurring painkillers (endorphins and enkephalins).4 Many types of chronic pain are helped by exercise,5 6 7 though some types of physical activity may aggravate certain painful conditions.8 People who want to initiate an exercise program for increasing pain tolerance should first consult a qualified health professional.
Nutritional supplements that may be helpful for pain
Certain amino acids have been found to raise pain thresholds and increase tolerance to pain. One of these, a synthetic amino acid called D-phenylalanine (DPA), decreases pain by blocking the enzymes that break down endorphins and enkephalins, the body’s natural pain-killing chemicals.9 10 DPA may also produce pain relief by other mechanisms, which are not well understood.11
In animal studies, DPA decreased chronic pain within 15 minutes of administration and the effects lasted up to six days.12 It also decreased responses to acute pain. These findings have been independently verified in at least five other studies.13 14 Clinical studies on humans suggest DPA may inhibit some types of chronic pain, but it has little effect on most types of acute pain.15 16
Most human research has tested the pain-relieving effects of 750 to 1,000 mg per day of DPA taken for several weeks of continuous or intermittent use. The results of this research have been mixed, with some trials reporting efficacy,17 18 19 others reporting no difference from placebo,20 and some reporting equivocal results.21 It appears that DPA may only work for some people, but a trial period of supplementation seems worthwhile for many types of chronic pain until more is known. If DPA is not available, a related product, D,L-phenylalanine (DLPA), may be substituted at amounts of 1,500 to 2,000 mg per day.
As early as 1981, preliminary human research showed that DPA made the pain-inhibiting effects of acupuncture stronger.22 One controlled animal study23 and two controlled trials in humans24 25 showed that DPA taken the day before acupuncture increased the effectiveness of acupuncture in reducing both acute dental and chronic low back pain.
Other amino acids may be beneficial in reducing pain. In the central nervous system, L-tryptophan serves as a precursor to serotonin. Serotonin participates in the regulation of mood and may alter responses to pain. In a preliminary trial, 2,750 mg per day of L-tryptophan decreased pain sensitivity.26 Another preliminary trial found that L-tryptophan (500 mg every four hours) taken the day before a dental procedure significantly decreased the postoperative pain experienced by patients.27 In another preliminary trial, 3 grams of L-tryptophan taken daily for four weeks significantly decreased pain in a group of people with chronic jaw pain.28 No research has been published investigating the pain control potential of 5-hydroxytryptophan (5-HTP), another serotonin precursor that, unlike L-tryptophan, is currently available without a prescription.
Vitamin B12 has exhibited pain-killing properties in animal studies.29 In humans with vertebral pain syndromes, injections of massive amounts of vitamin B12 (5,000 to 10,000 mcg per day) have reportedly provided pain relief.30 Further studies are needed to confirm the efficacy of this treatment.
Are there any side effects or interactions with pain?
Refer to the individual supplement for information about any side effects or interactions.
Herbs that may be helpful for pain
Capsaicin is an extract of cayenne pepper that may ease many types of chronic pain when applied regularly to the skin. In animal studies, capsaicin was consistently effective at reducing pain when given by mouth, by injection, or when applied topically.31 32 A controlled trial in humans found that application of a solution of capsaicin (0.075%) decreased sensitivity of skin to all noxious stimuli.33 One review article deemed the research on capsaicin’s pain-relieving properties “inconclusive.”34 However, in several uncontrolled and at least five controlled clinical trials, capsaicin has been consistently shown to decrease the pain of many disorders, including trigeminal neuralgia, shingles, diabetic neuropathy, osteoarthritis, and cluster headaches.35 36 37 38 39 For treatment of chronic pain, capsaicin ointment or cream (standardized to 0.025 to 0.075% capsaicin) is typically applied to the painful area four times per day.40 It is common to experience stinging and burning at the site of application, especially for the first week of treatment; avoid getting it in the eyes, mouth, or open sores.
Preliminary reports from Chinese researchers also note that 75 mg per day of THP (an alkaloid from the plant corydalis) was effective in reducing nerve pain in 78% of of those tested.41
As early as 1763, use of willow bark to decrease pain and inflammation was reported.42 Its constituents are chemically related to aspirin. These constituents may decrease pain by two methods: by interfering with the process of inflammation, and by interfering with pain-producing nerves in the spinal cord.43 No human studies have investigated the pain-relieving potential of willow bark, and questions have been raised as to the actual absorption of willow bark’s pain-relieving constituents.44 The potential pain-reducing action of willow is typically slower than that of aspirin.
In animal research, alcohol/water extracts of plants from the genus phyllanthus (25 to 200 mg per 2.2 pounds body weight) have shown a marked ability to decrease pain.45 This family includes the plants Phyllanthus urinaria, P. caroliniensis, P. amarus, and P. niruri. Like aspirin, phyllanthus extracts appear to reduce pain by decreasing inflammation.46 Although they are six to seven times more potent than aspirin or acetaminophen47 in test tube studies, extracts of these plants also demonstrate liver-protective properties,48 suggesting they may be safer than drugs such as acetaminophen, which has well-documented toxicity to the liver. The usefulness of phyllanthus extracts for treating pain in humans is unknown.
Other herbs that have been historically used to relieve pain (although there are no modern scientific studies yet available) include valerian, passion flower, American scullcap, Piscidia erythrina, and crampbark (Viburnum opulus).
Are there any side effects or interactions with pain?
Refer to the individual herb for information about any side effects or interactions.
Holistic approaches that may be helpful for pain
Transcutaneous electrical nerve stimulation (TENS) is a form of electrical physical therapy that has been used in the treatment of pain since the early 1970s. Pads are placed on the skin and a mild electrical current is sent through to block pain sensations. Many TENS units are small, portable, and may be hidden under clothing. A review of the first ten years of research on TENS described success rates in treating chronic pain varying from 12.5% to 92% after one year of treatment.49 Variations in success rates were attributed to differences in the type of pain the TENS was treating. More current research identifies specific conditions that consistently respond well to TENS therapy:50 51 rheumatoid arthritis, osteoarthritis, low back pain, phantom limb pain, and post-herpetic nerve pain (shingles). Pain caused by pinched nerves in the spine responds poorly to TENS therapy. While a small number of controlled trials have reported no benefit,52 53 most evidence suggests TENS is an effective form of therapy for many types of pain.54 55 56
Relaxation exercises may decrease the perception of pain. Pain increases as anxiety increases; using methods to decrease anxiety may help reduce pain.57 In one controlled hospital study, people who were taught mind-body relaxation techniques reported less pain, less difficulty sleeping, and fewer symptoms of depression or anxiety than did people who were not taught the techniques.58
Acupuncture has been shown to decrease pain by acting on the enkephalin-based, pain-killing pathways.59 In 1997, the National Institutes of Health (NIH) stated that acupuncture is useful for muscular, skeletal, and generalized pain, as well as for anesthesia and post-operative pain. The NIH statement was based on a critical review of over 67 controlled trials of acupuncture for pain control.
Practitioners of manipulation report that it often produces immediate pain relief either in the area manipulated or elsewhere.60 Controlled trials have found that people given spinal manipulation may experience reduction in pain sensitivity of the skin in related areas,61 62 a reduction in joint and muscle tenderness in the area manipulated,63 and a decrease in elbow tenderness when the neck was manipulated.64 One study showed no effect of lower spine manipulation on sensitivity to deep pressure over low back muscles and ligaments.65 Some researchers have speculated that joint manipulation affects pain by enhancing the effects of endorphins. However, only one66 of three67 68 controlled studies has shown an effect of manipulation on endorphin levels.
Hypnosis has been shown to significantly reduce pain associated with office surgical procedures that are performed while the patient is conscious (i.e., without general anesthesia).69 People undergoing office surgical procedures received standard care, structured attention or self-hypnotic relaxation in one study. Those using self-hypnosis had no increases in pain during the procedures, compared to those in the other groups. Hypnosis also appeared to stabilize bleeding, decrease the requirement for narcotic pain drugs during the procedure, and shorten procedure time.