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.^1,2 A controlled trial in humans found that application of a solution of capsaicin (0.075%) decreased sensitivity of skin to all noxious stimuli.³ One review article deemed the research on capsaicin’s pain-relieving properties “inconclusive.”⁴ 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.^5,6,7,8,9 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.¹⁰ 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 those tested.²¹

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.^22,23 DPA may also produce pain relief by other mechanisms, which are not well understood.²⁴

In animal studies, DPA decreased chronic pain within 15 minutes of administration and the effects lasted up to six days.²⁵ It also decreased responses to acute pain. These findings have been independently verified in at least five other studies.^26,27 Clinical studies on humans suggest DPA may inhibit some types of chronic pain, but it has little effect on most types of acute pain.^28,29

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,^30,31,27 others reporting no difference from placebo,³³ and some reporting equivocal results.³⁴ 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.³⁵ One controlled animal study³⁶ and two controlled trials in humans^37,38 showed that DPA taken the day before acupuncture increased the effectiveness of acupuncture in reducing both acute dental and chronic low back pain.

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).

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).³⁸

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).

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).

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.³⁹ 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.⁴⁰ Although they are six to seven times more potent than aspirin or acetaminophen⁴¹ in test tube studies, extracts of these plants also demonstrate liver-protective properties,⁴² 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).⁴³

Vitamin B12 has exhibited pain-killing properties in animal studies.⁴⁴ 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.⁴⁵ Further studies are needed to confirm the efficacy of this treatment.

As early as 1763, use of willow bark to decrease pain and inflammation was reported.⁴⁶ 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.⁴⁷ 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.⁴⁸ The potential pain-reducing action of willow is typically slower than that of aspirin.