** Shares of Vallon Pharmaceuticals Inc VLON.O more than
doubles to 53 cents, set for their best day, if gains hold
** Stock among top three heaviest vols across U.S. exchanges
** Co to combine with privately held biotech GRI Bio through
an all-stock reverse merger; GRI will join a unit of VLON
** Deal expected to close in Q1 2023, after which combined
co will trade on Nasdaq as GRI Bio Inc with ticker "GRI"
** Nearly 77 mln shares traded hands, about 106x of stock's
25-DMA
** VLON stock down nearly 96% YTD through last close;
majority of those losses happened in March after its ADHD
experimental treatment failed to meet late-stage trial goals
(Reporting by Ruhi Soni in Bengaluru)
((Ruhi.Soni@thomsonreuters.com
Twitter: https://twitter.com/ruhithere))