People mainly take L-Phenylalanine for mood, energy. Based on 12 first-hand reports and 9 meta-analyses & systematic reviews in the medical literature. Ranked #884 of 1,974 overall.
Of reports that state an outcome, 100% are positive.
Of the people who reported each effect, the share who said it got better.
Systematic reviews and meta-analyses from PubMed, with their published conclusions.
3+ meta-analyses or systematic reviews and 10+ randomized controlled trials in humans. The grade measures how much human research exists — read the conclusions below for what it found.
Conclusion: Further studies over the long term, assessing a range of appetite-regulating hormones and comparing aspartame with other LCS, would be of value. This study was registered in PROSPERO as CRD42024540781 on April 29, 2024.
PubMed 40381807 ↗Conclusion: The greater satiating efficacy of LEU versus PHE was significantly dissociated from the effects of these AAs on PYY, while the greater satiating potency of TRP versus PHE was significantly dissociated from the effects of these AAs on insulin and glucagon. In contrast, ghrelin and CCK, and potentially other mechanisms, including central sensing of individual AAs, appear to be stronger candidate mechanisms for the relative satiating effects obtained.
PubMed 29138359 ↗Conclusion: Reports investigating the efficacy of NHPs for vitiligo exist, but are of poor methodological quality and contain significant reporting flaws. L-phenylalanine used with phototherapy, and oral Ginkgo biloba as monotherapy show promise and warrant further investigation.
PubMed 18498646 ↗Conclusion: A restricted set of five single biomarkers (interleukin-8, choline, pipecolinic acid, l-phenylalanine, and S-carboxymethyl-l-cysteine) as well as combined biomarkers demonstrated excellent diagnostic test accuracy. The present systematic review confirms the potential value of a selected set of salivary biomarkers as diagnostic tools for head and neck carcinoma.
PubMed 26170140 ↗As stated by users — not a recommendation. Follow the label or your doctor.
How often each side effect came up across all reports.
Verbatim quotes, shortened only — each links to the original discussion.
“Dopamine precursor - l-phenylalanine or l-tyrosine. I usually skip this.”
“L-Phenlalanine is great for long term use.”
“L-Phenylalanine 500 mg”
“I find L-Tyrosine and L-Phenylalinine give me a daily boost of energy if I take them in the morning”
“In particular L-phenylalanine, I believe. [ADHD symptoms can be exacerbated by nutritional deficiencies]”
User data from public discussions; research from PubMed. Information only, not medical advice — talk to a doctor before starting, stopping or combining anything. Data updated October 2, 2026. How we rate