Cidara Therapeutics Stock Rockets Over 700% This Year — Then Wall Street Turns Neutral On Merck Takeover

• Merck’s all-cash agreement grants it access to Cidara’s lead flu-prevention antibody, CD388, which has received FDA Breakthrough Therapy designation and is currently in late-stage studies enrolling more than 6,000 participants.
• Major brokerages moved to neutral stances following the announcement.
• Retail traders reacted on Stocktwits, with many celebrating long-held gains.

Cidara Therapeutics, up more than 700% this year, more than doubled on Friday after Merck unveiled a $9.2 billion all-cash takeover, only for major Wall Street firms to turn neutral on the biotech following the deal’s announcement.

The deal values Cidara at $221.50 per share, representing a roughly 109% premium to Thursday’s close, and is expected to close in the first quarter of 2026, subject to customary conditions.

Analysts Cut Ratings After Deal Announcement

Despite the stock surge, major brokerages shifted to neutral stances across the board. Morgan Stanley downgraded Cidara to ‘Equal Weight’, JPMorgan moved to ‘Neutral’, RBC Capital to ‘Sector Perform’, and Needham shifted to ‘Hold’. H.C. Wainwright also stepped back to ‘Neutral’. 

Merck’s Strategic Push Ahead Of Keytruda Patent Expiry

Merck said the takeover strengthens its respiratory pipeline ahead of the anticipated 2028 patent loss for Keytruda, its top-selling cancer therapy that generated more than $25 billion last year. The move follows Merck’s $10 billion acquisition of Verona Pharma in July, part of a series of large deals aimed at building future revenue streams.

Cidara brings Merck its lead candidate, CD388, a long-acting antibody designed to prevent influenza infection in high-risk individuals. The U.S. Food and Drug Administration has granted CD388 Breakthrough Therapy designation, potentially speeding its review. The program is currently in late-stage studies across high-risk populations, including immunosuppressed patients who cannot receive seasonal flu vaccines and adults aged 65 and older. More than 6,000 participants are expected to be enrolled globally by the end of the month.

Competitive Bidding And Rising Value

Discussions reportedly extended late into Thursday as Merck faced competition from another pharmaceutical group before its winning bid was selected. The high demand reflects growing interest in long-acting influenza prevention technologies, particularly for vulnerable populations.

Cidara has been among the sector’s strongest performers in recent months. Its shares have been fueled by robust clinical data, speculation about a potential auction, and rising interest in CD388’s commercial prospects. The frenzy comes amid a broader wave of pharmaceutical dealmaking, including Pfizer’s recent win over Novo Nordisk in the race for obesity-drug developer Metsera in a deal worth up to $10 billion.

Stocktwits Users Celebrate Big Payday

On Stocktwits, retail sentiment was ‘extremely bullish’ for Cidara and ‘bullish’ for Merck, with both seeing elevated message activity ranging from ‘extremely high’ to ‘high’.

Some users said they had waited a long time for this outcome and thanked the Cidara team as they exited their positions, while others congratulated holders, noting that the deal delivered major gains for many investors.

Merck’s stock has declined 4% so far in 2025.

For updates and corrections, email newsroom[at]stocktwits[dot]com.

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