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Amino Acid

L-Phenylalanine

Also known as: Phenylalanine, Phe, DL-Phenylalanine, DLPA

B
Evidence

Essential amino acid and precursor to tyrosine, dopamine, and other catecholamines. Important for mood, cognitive function, and pain modulation.

Last reviewed June 2026 · Evidence graded from peer-reviewed research, not editorial opinion. Educational only — not medical advice.

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Primary uses

  • Mood support
  • Cognitive function
  • Pain management (DLPA)
  • Dopamine precursor

How it works

  • Converted to L-tyrosine by PAH enzyme
  • Precursor to dopamine, norepinephrine, epinephrine
  • D-form inhibits enkephalin degradation
  • Supports melanin synthesis

Dosage

Typical range
500-2000 mg daily
Timing
On empty stomach for mood effects
With food
Without for absorption
Duration
Cycle for mood use
Special populations
Not for PKU patients

Forms

  • Capsule
  • Powder

Safety

Common side effects

  • Headache
  • Anxiety at high doses

Contraindications

  • Phenylketonuria (PKU)
  • MAOIs

Products containing L-Phenylalanine

Top-scoring supplements in our catalog that list L-Phenylalanine on the label. Each product is graded on Formulate's ingredient-level rubric — dose accuracy, form, transparency, and third-party testing.

Thorne
Amino Complex - Berry
84
Thorne
Amino Complex - Lemon
84
Thorne
Amino Complex
80
See all products →

Evidence notes

Established precursor role in neurotransmitter synthesis

Grade B: Some human trials support key claims; further confirmation needed.

L-Phenylalanine compared head-to-head

Related in Amino Acid

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Medical disclaimer. This page is educational and does not replace advice from a qualified healthcare provider. Individual needs and risks vary — consult a professional before starting, stopping, or combining supplements, especially if you are pregnant or nursing, taking medication, or managing a health condition.