Diet & Fitness

Several animal studies and some research involving humans suggest that a synthetic version of the natural amino acid phenylalanine called D-phenylalaline (DPA), reduces pain by decreasing the enzyme that breaks down endorphins.¹ It is less clear whether DPA may help people with LBP, though there are a small number of reports to that effect,² including one uncontrolled report of 27 of 37 people with LBP experiencing “good to excellent relief.”³ In a double-blind trial, University of Texas researchers found that 250 mg of DPA four times per day for four weeks was no more effective than placebo for 30 people with various types of chronic pain; 13 of these people had low back pain.⁴ In a Japanese clinical trial, 4 grams of DPA per day was given to people with chronic low back pain half an hour before they received acupuncture.⁵ Although not statistically significant, the results were good or excellent for 18 of the 30. The most common supplemental form of phenylalanine is D,L-phenylalanine (DLPA). Doctors typically recommend 1,500–2,500 mg per day of DLPA.

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.^6,7 DPA may also produce pain relief by other mechanisms, which are not well understood.⁸

In animal studies, DPA decreased chronic pain within 15 minutes of administration and the effects lasted up to six days.⁹ It also decreased responses to acute pain. These findings have been independently verified in at least five other studies.^10,11 Clinical studies on humans suggest DPA may inhibit some types of chronic pain, but it has little effect on most types of acute pain.^12,13

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,^14,15,11 others reporting no difference from placebo,¹⁷ and some reporting equivocal results.¹⁸ 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.¹⁹ One controlled animal study²⁰ and two controlled trials in humans^21,22 showed that DPA taken the day before acupuncture increased the effectiveness of acupuncture in reducing both acute dental and chronic low back pain.

Several animal studies and some research involving humans suggest that a synthetic version of the natural amino acid phenylalanine called D-phenylalaline (DPA), reduces pain by decreasing the enzyme that breaks down endorphins.²² It is less clear whether DPA may help people with LBP, though there are a small number of reports to that effect,²³ including one uncontrolled report of 27 of 37 people with LBP experiencing “good to excellent relief.”²⁴ In a double-blind trial, University of Texas researchers found that 250 mg of DPA four times per day for four weeks was no more effective than placebo for 30 people with various types of chronic pain; 13 of these people had low back pain.²⁵ In a Japanese clinical trial, 4 grams of DPA per day was given to people with chronic low back pain half an hour before they received acupuncture.²⁶ Although not statistically significant, the results were good or excellent for 18 of the 30. The most common supplemental form of phenylalanine is D,L-phenylalanine (DLPA). Doctors typically recommend 1,500–2,500 mg per day of DLPA.

Supplementation with D-phenylalanine (DPA), a synthetic variation of the amino acid, L-phenylalanine (LPA), has reduced chronic pain due to osteoarthritis in a preliminary trial.²⁷ In that study, participants took 250 mg three to four times per day, with pain relief beginning in four to five weeks. Other preliminary trials have confirmed the effect of DPA in chronic pain control,²⁸ but a double-blind trial found no benefit.²⁹ DPA inhibits the enzyme that breaks down some of the body’s natural painkillers, substances called enkephalins, which are similar to endorphins. An increase in the amount of enkephalins may explain the reported pain-relieving effect of DPA. If DPA is not available, a related product, D,L-phenylalanine (DLPA), may be substituted (1,500 to 2,000 mg per day). Phenylalanine should be taken between meals, because protein found in food may compete for uptake of phenylalanine into the brain, potentially reducing its effect.³⁰

D-phenylalanine has been used with mixed results to treat chronic pain, including pain caused by RA.³¹ No research has evaluated the effectiveness of DL-phenylalanine, a related supplement, in treating people with RA. The effect of either form of phenylalanine in the treatment of people with RA remains unproven.

L-phenylalanine is another amino acid that converts to mood-affecting substances (including phenylethylamine and norepinephrine). Preliminary research reported that L-phenylalanine improved mood in most of the depressed people studied.³²DLPA is a mixture of the essential amino acid L-phenylalanine and its synthetic mirror image, D-phenylalanine. DLPA (or the D- or L- form alone) reduced depression in 31 of 40 people in a preliminary trial.³² Some doctors suggest a one-month trial with 3–4 grams per day of phenylalanine for people with depression, although some researchers have found that even very low amounts—75–200 mg per day—were helpful in preliminary trials.³⁴ In one double-blind trial, depressed people given 150–200 mg of DLPA per day experienced results comparable to that produced by an antidepressant drug.³⁵

Supplementation with the amino acid L-phenylalanine (LPA) may have value when combined with ultraviolet (UVA) light therapy. Several clinical trials, including one double-blind trial, indicated that LPA (50 mg per 2.2 pounds of body weight per day—3,500 mg per day for a 154-pound person—or less) increased the extent of repigmentation induced by UVA therapy. LPA alone also produced a more modest repigmentation in some people.³⁵ A study of vitiligo in children reported that LPA plus UVA was an effective treatment in a majority of the children.³⁶

A group of Spanish doctors reported on their experience using LPA over a six-year period. Some of the 171 people with vitiligo received LPA (50 or 100 mg per 2.2 pounds body weight per day) for up to three years. Between April and October of each year, participants also applied a 10% LPA gel, prior to exposing their skin to the sun for 30 minutes. Some improvement was seen in 83% of participants, and the results were rated as good in 57% (75% improvement or better).³⁷