What each catalyst does to the price

How far a catalyst moves a stock depends less on the event itself than on four things: how surprising the result is versus expectations, how dependent the company is on that one asset, how the stock is positioned going in (run-up, short interest, float), and its cash position. The ranges below are rough tendencies for small/mid-cap biotech — large caps move far less.

Clinical readouts

• Phase 3 success (primary endpoint met): often +30% to +100%+ for a single-asset small cap — but muted or even negative if heavily run-up (sell the news).
• Phase 3 failure (endpoint missed): brutal, frequently -50% to -80%, sometimes more for one-drug companies.
• Phase 2 positive: a meaningful re-rate (+20% to +60%) as the program de-risks; a miss can halve the stock.
• Phase 1: usually smaller (safety/PK only) unless early efficacy surprises.
• Interim / DSMB stop for efficacy: big positive; stop for futility or safety: big negative.

FDA decisions

• Approval: a pop if unexpected, but commonly a 'sell the news' fade when the date and outcome were anticipated; larger for first-in-class or contested approvals.
• Complete Response Letter (CRL / rejection): sharp drop, often -20% to -50%, worse if the fix needs new trials.
• Advisory Committee (AdComm) vote: highly volatile — a favorable vote pops the stock, an unfavorable one sinks it, frequently 20%+ either way.
• Clinical hold: sharp negative.

Designations & filings

• Breakthrough / Fast Track / Orphan / Priority Review: modest positive (+5% to +20%) — validation and faster timelines, not approval.
• NDA/BLA acceptance: mild positive (it starts the PDUFA clock).

Corporate events

• Partnership / licensing deal: positive and often sustained — non-dilutive cash plus a credibility stamp; scales with the upfront and the partner.
• M&A (as target): jumps toward the offer price, typically a sizable premium.
• Offering / PIPE: negative — new shares at a discount, usually -5% to -20% on the print, worse for low-runway names.

What amplifies the move

• Surprise vs. expectations — a 'good' result that was priced in can still fall.
• Pipeline concentration — single-asset companies gap hardest in both directions.
• Positioning — a big run-up invites a fade; a crowded short adds squeeze fuel.
• Float & liquidity — thin floats exaggerate moves.
• Cash / runway — a weak balance sheet turns any spike into a dilution opportunity.

These are tendencies, not rules — and not financial advice. The same event can produce opposite moves depending on what was already priced in.