Viking stock has slipped more than 20% from its peak.Viking Therapeutics (VKTX -0.54%) soared to center stage earlier this year as a potentially promising player in one of today's highest-growth healthcare markets: weight loss drugs. The biotech company presented solid data for a candidate that could eventually rival blockbuster weight loss drugs from big pharma companies Eli Lilly and Novo Nordisk. And in just one trading session, the shares skyrocketed, rising more than 100%.Since then, Viking has reitera ...