(Adds share movement, conference call comment)
By Manojna Maddipatla
Dec 6 (Reuters) - Supernus Pharmaceuticals Inc's treatment for attention deficit hyperactivity disorder met the main goal of two trials, but shares fell about 16 percent on Thursday as the data failed to convince some investors that the drug was better than rivals.
Shares of the drugmaker fell as much as 15.8 pct to $38.75.
The drug, SPN-812, is a non-stimulant and belongs to the same class of medicine as Eli Lilly and Co's Strattera and Shire Plc's Intuniv.
Analysts on average said that SPN-812 has failed to stand out from existing treatment options for ADHD. But if Supernus is able to show that its drug takes effect quicker and causes fewer side effects than rival drugs, the company could benefit.
The two placebo-controlled studies tested three doses of SPN-812 and the company said it proved effective in reducing symptoms such as hyperactivity and lack of attention in affected children aged six to 11 in both the studies.
In one trial, patients showed statistically significant results as early as a week into treatment on two doses, Supernus said.
The drug was shown to be safe across all doses, with a few adverse reactions such as headache, decreased appetite and fatigue.
"The studies reached statistical significance on their primary endpoints...but not at a level that represents a clear standout from Strattera," Stifel analyst Annabel Samimy said.
The analyst also added that the drug's early onset of action was important as slow onset has been a primary complaint among other non-stimulants.
The company said on a conference call that SPN-812 would be able to capture 3-5 percent of the ADHD market.
Brokerage Mizuho Securities sees promising yields if the treatment gets U.S. approval. The drug could be commercially compelling despite a weaker-than-expected data, Mizuho said, estimating sales of about $600 million in 2025.
"Supernus has a good drug, with a good profile, in a huge market," Cowen analyst Ken Cacciatore said.
Children with ADHD, a common developmental disorder, often have trouble paying attention and controlling compulsive behavior.
Preliminary data from two other late-stage studies evaluating SPN-812 in adolescents are expected by end of the first quarter of 2019, the company said. (Reporting by Manogna Maddipatla in Bengaluru; Editing by Bernard Orr and Shinjini Ganguli)