L1-79 and Autism: What Families Should Know About the Research

Published September 13, 2026

A plain-language review of what L1-79 is, what early Phase 2 findings do and do not show, and why this experimental drug is not yet an established autism treatment.

L1-79 and Autism: What Families Should Know About the Research

Bottom line: L1-79 is an experimental drug being studied for socialization and related outcomes in individuals on the autism spectrum. Early results are interesting, but they do not yet prove that the drug is effective or safe for routine use. L1-79 is not approved for any indication, and FDA Fast Track status is not approval.

What is L1-79?

L1-79 is an oral investigational drug developed by Yamo Pharmaceuticals. Trial records describe it as D,L-alpha-methyltyrosine, a mixture of two molecular forms. It inhibits tyrosine hydroxylase, an enzyme involved in making the catecholamines dopamine, norepinephrine and epinephrine.

Catecholamines help regulate attention, arousal, mood, movement and reward. Researchers are studying whether changing this signalling could affect social functioning for some individuals on the autism spectrum. That is a scientific hypothesis, not an established explanation of autism.

L1-79 is related to metyrosine, a medicine approved in the United States for a rare adrenal tumour called pheochromocytoma. Metyrosine is not approved as an autism treatment and should not be treated as a substitute for L1-79.

What human research is available?

An eight-person case series

A 2019 paper described eight participants, ages 2.75 to 24 years, who received L1-79 for eight weeks. Seven had improvement on some rating scales, and three mild adverse events were reported. However, everyone received the drug, there was no placebo group, and the lead author was affiliated with the manufacturer. The authors said controlled studies were needed.

A short Phase 2 safety study

A registered study called NCT02947048 enrolled 42 males ages 12 to 21. It included open-label and randomized, placebo-controlled portions lasting four weeks. The primary outcome was safety. ClinicalTrials.gov says the study was too small to reliably detect efficacy changes and had missing or incomplete caregiver questionnaire data.

No deaths or serious adverse events were reported in that study. Events recorded during treatment included diarrhea, urine crystals, one seizure and one fainting episode, among other isolated events. A small trial cannot determine whether the drug caused every event or identify rare and long-term risks.

A later 58-person Phase 2 study

NCT05067582 enrolled 58 participants ages 12 to 21 in a randomized, double-blind, placebo-controlled crossover trial. It was completed in June 2024.

In May 2025, Yamo reported that L1-79 had a 7.94-point advantage over placebo on the Vineland-3 Socialization Standard Score during the first study period, with a reported p-value of 0.01. The company also reported no serious adverse events and no withdrawals due to side effects while participants were receiving L1-79.

Those findings are encouraging but incomplete. They came from a company press release and conference presentation, not a peer-reviewed full paper. The company-hosted poster says carryover and sequence effects made the planned crossover analysis unusable, so efficacy analysis was limited to the first period. The highlighted Vineland standard score is listed as a secondary outcome in the trial registry, while the registered primary outcome is a responder analysis. ClinicalTrials.gov does not yet contain summary results for this study, so families and independent researchers cannot review the full analysis and safety tables.

How strong are the biological claims?

Who was represented in the trials?

Most controlled evidence comes from adolescents and young adults ages 12 to 21. The first controlled trial enrolled males only. The later study allowed all sexes but required participants to meet language and testing criteria, have an IQ estimate around 70 or higher, have regular caregiver involvement and be able to swallow capsules.

The findings therefore should not be generalized to young children, older adults, people who communicate without speech, people with higher support needs or people with many co-occurring medical conditions.

What does FDA Fast Track mean?

Yamo reported that the FDA granted L1-79 Fast Track designation in 2018. Fast Track can give a company more frequent communication with the FDA and may speed parts of development or review. It does not mean the drug has been approved, proven effective or fully assessed for safety.

As of September 2026, ClinicalTrials.gov lists two completed L1-79 studies and no recruiting Phase 3 trial. Yamo says it plans to begin Phase 3 in early 2027 but still needs funding, sites and participants. Families should rely on an official trial registry before assuming that recruitment is open.

No public Canadian product authorization or L1-79 trial was found in Health Canada's Drug Product Database and clinical-trial portal. That does not rule out every form of regulator-authorized special access, but families should not treat a company announcement as Canadian approval or trial authorization.

What should families do now?

L1-79 may prove useful, or larger studies may show that the early signal does not hold up. For now, the most accurate description is promising but unproven.

Sources

Evidence checked 8 September 2026. This article is educational and does not provide medical advice or recommend a drug. Discuss individual health and research-participation decisions with a qualified healthcare professional.

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