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Ingredients

DL-Phenylalanine

Phenylalanine · DLPA · L-Phenylalanine

Snapshot

IndicationsContraindications
  • Reward processing1, 2
  • Postprandial glucose response3
  • Phenylketonuria4
  • Monoamine oxidase inhibitor use4
  • Pregnancy or lactation4

DL-Phenylalanine is a racemic mix of the essential amino acid L-phenylalanine and its mirror-image D-form, with the L-form converted to tyrosine and supporting dopamine synthesis. People take it for mood and motivation, a rationale drawn largely from depletion studies in which lowering phenylalanine and tyrosine availability reduced reward-driven behavior1, 2.

Human data on supplemental phenylalanine for mood remain indirect, resting on those depletion paradigms. In a 2021 cross-sectional urinary metabolomic study of elderly stroke survivors, lower urinary phenylalanine tracked with more depressive symptoms; no trial has tested supplementation there. Products listing DL-phenylalanine come mostly as capsules and powders; see Form comparison.

Phenylketonuria is the most consequential exclusion: impaired conversion to tyrosine lets phenylalanine accumulate, and temporary elevation produced reversible white matter changes in adults with the disorder5. Per product labels, monoamine oxidase inhibitor antidepressants, levodopa, and antipsychotics are listed among medicines that bar use4, and some labels also bar use in pregnancy or nursing4.

Last updated October 16, 2026. Read how we make monographs.

In the full monograph

60 sources, 42 studies

  • When to useThe situations practitioners use it for, each with the reason and the study behind it.
  • SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
  • InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
  • Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
  • How it worksWhat it is and how it works in the body, in plain terms.
  • Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
  • Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
  • Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.
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Sources

  1. 1The subjective and cognitive effects of acute phenylalanine and tyrosine depletion in patients recovered from depression.pubmed.ncbi.nlm.nih.govRoiser, McLean, Ogilvie et al. · Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology · 2005 · Pubmed
  2. 2Acute phenylalanine/tyrosine depletion reduces motivation to smoke cigarettes across stages of addiction.pubmed.ncbi.nlm.nih.govVenugopalan, Casey, O'Hara et al. · Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology · 2011 · Pubmed
  3. 3Effects of L-Phenylalanine on Energy Intake and Glycaemia-Impacts on Appetite Perceptions, Gastrointestinal Hormones and Gastric Emptying in Healthy Males.pubmed.ncbi.nlm.nih.govFitzgerald, Manoliu, Herbillon et al. · Nutrients · 2020 · Pubmed
  4. 4US product labelsdsld.od.nih.govWarnings printed on US dietary supplement labels with this ingredient, from the NIH Office of Dietary Supplements' Dietary Supplement Label Database (DSLD). Manufacturers' precautions, not evidence of harm
  5. 5Reversible white matter changes following a 4-week high phenylalanine exposure in adults with phenylketonuria.pubmed.ncbi.nlm.nih.govMuri, Reed, Maissen-Abgottspon et al. · Journal of inherited metabolic disease · 2025 · Pubmed