tuneTypical Dose
Not established for performance outcomes
Amino Acid
L-Phenylalanine
L-Phenylalanine (2-amino-3-phenylpropanoic acid)
Evidence TierDWADA NOT PROHIBITED
watchEffect Window
Acute physiologic effects. Long-term outcomes not established
check_circleCompliance
WADA NOT PROHIBITED
Overview
Clinical Summary
L-phenylalanine is an essential amino acid precursor to tyrosine with limited acute metabolic data and no reliable standalone mood or nootropic evidence.
Evidence for mood benefits is mixed, with small studies suggesting possible antidepressant effects in some individuals. Early research explored analgesic effects via endorphin-related pathways, but findings are inconsistent. Minority protocols combine phenylalanine with UV therapy for vitiligo, with variable outcomes. Benefits are uncertain and phenylketonuria is a strict contraindication.
L-Phenylalanine is an essential amino acid precursor to tyrosine with limited controlled human evidence for acute endocrine and glycemic changes.
Outcomes
What This Is Expected To Influence
Primary Outcomes
- Acute hormone and glucose handling shifts in a controlled crossover context.
Secondary Outcomes
- No consistent appetite suppression in the same controlled trial. Historical mood findings from uncontrolled studies are weak.
Safety
Contraindications and Interactions
Contraindications
- PKU
- PAH deficiency
- Uncontrolled blood pressure
- Active unstable psychiatric disease
- Pregnancy without specialist
Side effects
- Headache
- Nausea
- Heartburn
- Contraindicated in PKU
Interactions
- MAOI
- Sympathomimetics
- Thyroid-active agents
Avoid if
- Active malignancy
- Unstable cardiovascular disease
Evidence
Study-level References
l-phenylalanine-SRC-PHEO-001Randomized, double-blind, placebo-controlled crossover.
Sourceopen_in_newAmin AJ et al. Diabetes Obes Metab. 2021;23(1):147-157. PubMed PMID 32991046; DOI 10.1111/dom.14204.
Population: Healthy adults, acute dosing context.
Dose protocol: 10 g L-Phenylalanine compared with D-Phenylalanine and placebo.
Key findings: Increases insulin, glucagon, GIP and reduces glucose AUC\(_{70-150}\). No significant appetite or intake change.
Notes: Small cohort and short duration. Physiologic endpoints only.
Paper content
Increases insulin, glucagon, GIP and reduces glucose AUC\(_{70-150}\); no significant appetite or intake change.
l-phenylalanine-SRC-PHEO-002Open clinical study (no randomized control).
Sourceopen_in_newBeckmann H et al. J Neural Transm. 1977;41(2-3):123-134. PubMed PMID 335027; DOI 10.1007/BF01670277.
Population: 20 depressed patients with mixed diagnoses.
Dose protocol: DL-Phenylalanine 75-200 mg/day for 20 days.
Key findings: Clinical-impression and scale improvement in a majority subgroup. 4/20 non-responders, no controlled comparator.
Notes: High risk of selection bias, non-randomized design, no pure L-form, no placebo control.
Paper content
Clinical-impression and scale improvement in a majority subgroup; 4/20 non-responders, no controlled comparator.
l-phenylalanine-SRC-PHEO-003Practice guideline (evidence review + consensus).
Sourceopen_in_newVockley J et al. Genet Med. 2014;16(2):188-200. PubMed PMID 24385074; DOI 10.1038/gim.2013.157.
Population: Phenylalanine hydroxylase deficiency/PKU diagnosis and management.
Dose protocol: Life-long disease-management context, not supplement dosing endpoint.
Key findings: Strong evidence for monitoring and control targets, and against unsafe phenylalanine exposure in affected patients.
Notes: High quality for diagnosis and safety, not directly about nootropic benefits in healthy adults.
Paper content
Strong evidence for monitoring and control targets, and against unsafe phenylalanine exposure in affected patients.