There are two ways a product can be defective. It can be defectively designed, and it can be defectively manufactured.
If an engineer designs a car without a brake system, it’s defectively designed. If the engineer designed a car with a brake system, but the factory worker forgot to put the brakes on the car, it’s defectively manufactured.
For the most part, lawsuits against pharmaceutical companies don’t allege that a drug is defectively designed because the FDA approved the design of the drug. But sometimes, a lawsuit will allege that a drug is manufactured defectively. A recent example of this is the lawsuits filed against the makers of Digitek. Those lawsuits alleged that the Digitek tablets were defectively manufactured because they contained twice as much of the active ingredient than they were supposed to.
Basically, if a product is made to the exact specifications, but the specifications are dangerous, then the product is defectively designed. If the product doesn’t conform to the manufacturing specifications, then it’s defectively manufactured.