Yamo Pharmaceuticals, a clinical-stage biopharmaceutical company dedicated to treating the core symptoms of autism spectrum disorder (ASD), announced positive Phase 2 results for L1-79, presented at the International Society for Autism Research (INSAR) 2025 Annual Meeting.
The 12-week randomized, double-blind, placebo-controlled crossover study (n = 58, ages 12-21) showed statistically significant and clinically meaningful improvements in the Vineland-3 Socialization Standard Score (VSSS) and several secondary outcome measures during the first period, while maintaining a favorable safety profile. The VSSS is widely recognized as the gold-standard instrument for objectively measuring real-world social skills, directly addressing a core symptom of ASD.
Key Phase 2 Highlights
- Robust social improvement: L1-79 produced a 7.94-point advantage over placebo on the VSSS (p =0.01), nearly double the 4-point minimal clinically important difference (MCID) recognized by experts.1
- Clinical global impression: Investigator-rated severity (CGI-S) improved by ~0.6 points versus placebo (p < 0.02), indicating a meaningful reduction in overall socialization symptom burden.
- Caregiver-reported change: On the Caregiver Global Impression of Change in the three most bothersome symptoms of ASD (CaGI-3P), families reported mean improvements of 0.48–0.61 points (p < 0.05).
- Favorable safety and tolerability: L1-79 was generally safe and well tolerated, with no serious adverse events and no trial dropouts with L1-79 due to side effects.
“These results are extremely encouraging for the autism community,” said J. Thomas Megerian, MD, PhD, Chief Medical Officer at Yamo Pharmaceuticals. “Seeing nearly an 8-point jump in Vineland Socialization scores is remarkable. To our knowledge, this is one of the largest positive effects observed to date on an adaptive-behavior measure in ASD for any medication. More importantly, it represents a clinically meaningful change—essentially moving patients to a higher level of social functioning. For families and clinicians, that could translate to noticeable gains in real-life social engagement and independence.”
Dr. Megerian added that both clinician- and caregiver-reported global assessments corroborated the Vineland findings. Trial investigators rated participants on L1-79 as having lower overall symptom severity (CGI-S), and caregivers reported clear improvements in their loved ones’ most bothersome symptoms (CaGI-3P). “These global impression scales matter because they capture day-to-day life,” he explained. “For example, a parent might cite difficulty engaging in back and forth conversation, seeking friendship, showing flexibility, or engaging in repetitive behaviors or speech as top concerns—and on L1-79 we saw improvement across all of them. That kind of broad positive shift defines meaningful benefit in autism treatment.”
L1-79’s compelling efficacy may stem from its unique mechanism. The drug inhibits tyrosine hydroxylase, the rate-limiting enzyme for dopamine and norepinephrine production. Overactive catecholamine signaling has been tied to ASD-related social and sensory difficulties; by tempering this activity, L1-79 aims to rebalance circuits governing social interaction and communication. “Rather than chasing downstream symptoms, we’re modulating a core neural pathway,” noted Dr. Megerian. L1-79 is the first autism therapy to directly target catecholamine synthesis—an approach now backed by emerging research.
“With these compelling Phase 2 data, we are moving full speed into Phase 3 planning and FDA discussions,” said Chuck Bramlage, Chief Executive Officer of Yamo Pharmaceuticals. “Our mission is clear: bring the first medicine that meaningfully improves social functioning in autism to patients as quickly and responsibly
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