Why is a drug with 25 generic manufacturers in shortage?

Manufacturer count is a necessary but not sufficient condition for stable supply. A drug can have many registered manufacturers but still go on shortage when upstream supply chain or regulatory factors constrain the actual product flow.

Common mechanisms:

1. API (active pharmaceutical ingredient) sourcing is concentrated. Many generic manufacturers may source their API from the same 2-3 chemical plants, often in India or China. If those upstream suppliers have a quality issue or shutdown, all downstream manufacturers are affected simultaneously even though they appear to be independent.

2. Excipient or packaging constraints. Specific inert ingredients, propellants (HFA for albuterol inhalers), or container types may have limited suppliers. The albuterol shortage of 2023-2024 is a canonical example: 25+ manufacturers but constrained HFA propellant supply.

3. FDA enforcement action against one major manufacturer. When the FDA suspends or restricts production at a large facility, even if other manufacturers exist, market share concentration means a major share of supply disappears overnight.

4. Sudden demand spikes (Ozempic, Wegovy) outstripping even competitive supply.

For plan sponsors, manufacturer count is a green flag for PRICING resilience (more competition = lower NADAC) but not for SUPPLY resilience. Live shortage status from FDA is the relevant signal for member-disruption risk.