On September 17, Arrowhead Pharmaceuticals fell 5.41% in regular trading, trading at $66.79/share with turnover of $190 million, extending a multi-day selloff that began on September 15.

The decline follows the company's release on September 15 of interim topline clinical data for its first dual-function RNAi therapy targeting mixed hyperlipidemia. The announcement disclosed that the single ascending dose study had advanced to the 400-milligram dose level with no drug-related serious adverse events reported. While the safety profile was positive, the disclosure referenced only \"preliminary efficacy signals,\" with notably conservative language that raised investor concerns over the strength of efficacy data.

The cautious tone contrasted with prior catalysts that had supported the stock, including Redemplo's Phase 3 data showing an 80% median reduction in triglycerides from baseline, a positive CHMP opinion in Europe for Plozasiran, and a licensing deal with Madrigal Pharmaceuticals featuring up to $975 million in milestone payments. Profit-taking pressure has persisted since the initial 8.95% drop on September 15, as the market continues to reassess the dual-function program's near-term prospects.

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