In 1982, seven people in the Chicago area took Extra-Strength Tylenol capsules and died within hours. The cause was cyanide poisoning. Investigators found that someone had removed bottles from store shelves, opened the capsules, replaced the acetaminophen powder with potassium cyanide, and put the tampered bottles back on the shelves. Johnson & Johnson, the manufacturer, faced an immediate crisis. They recalled millions of bottles, pulled the product from all stores, and spent millions on public warnings. But the legal question that followed was not about catching the criminal. It was about whether the company was financially responsible for the deaths even though a stranger had deliberately poisoned the product after it left the factory. This case changed product liability law for contaminated medicine forever.

Under standard product liability rules, a manufacturer is strictly liable when a product leaves the factory in a defective condition and that defect causes injury. Strict liability means you do not have to prove the company was careless or negligent. You only have to prove the product was defective and the defect caused the harm. For medicine or food, a product is defective if it contains a foreign substance that makes it dangerous. A consumer who finds a shard of glass in a baby food jar does not need to prove the company failed to inspect the jar. The glass itself is proof of a defect. The same rule applies to medicine that contains a toxic chemical instead of the intended drug. The poison is the defect.

But the Tylenol case presented a twist. The cyanide was not in the capsules when they left the factory. Johnson & Johnson had quality control procedures in place. Their testing showed the bottles were safe when shipped. The tampering happened after the product was in stores, and it was the deliberate act of a stranger. The legal term for this situation is a superseding cause. A superseding cause is an event that happens after the manufacturer has done its job, that breaks the chain of responsibility, and that the manufacturer could not reasonably have predicted or prevented. At first glance, a random criminal poisoning product on a store shelf looks like the perfect example of a superseding cause. If that argument had held, Johnson & Johnson would have owed nothing to the victims’ families.

The courts did not buy that argument completely. The lawsuits that followed the Tylenol deaths forced judges to examine what a manufacturer should foresee and what duty it has once its product is in the hands of consumers. The key issue was not whether the company could stop a determined criminal. The issue was whether the product’s design was unreasonably dangerous because it allowed tampering to go undetected. The Tylenol capsules were easy to open and reseal without leaving any visible sign. The poison could be inserted, the capsule put back together, and the bottle returned to the shelf. A consumer could not tell anything was wrong just by looking. The plaintiffs argued that Johnson & Johnson should have known that a capsule design with no tamper-resistant features was dangerous. They argued that the company had a duty to warn consumers about the risk and a duty to make the product harder to tamper with.

This line of thinking brought the case under the legal theory of failure to warn. A manufacturer has a duty to warn about dangers that are not obvious to the ordinary user. For medicine, that duty includes telling consumers about risks they cannot see or detect by smell or taste. The tampering risk was not obvious in 1982. People did not routinely inspect over-the-counter capsules for holes or check bottle seals. Johnson & Johnson settled with the victims’ families out of court, but the legal impact went far beyond that settlement. The case effectively killed the market for non-tamper-resistant capsules. Within months, the Food and Drug Administration issued new regulations requiring tamper-evident packaging for all over-the-counter drugs. Johnson & Johnson itself led the industry in developing the triple-sealed packaging that became the standard.

The lasting legal lesson of the Tylenol case is that a manufacturer cannot always hide behind a criminal act. If the product’s design makes a foreseeable type of tampering easy and invisible, the company may be liable even though a stranger committed the crime. The duty runs from manufacturing through distribution and into the hands of the consumer. That duty includes anticipating how a product might be misused or attacked. For any company making food or medicine, the standard is clear. You must design your packaging with security in mind. You must inspect your supply chain. You must warn about dangers you know or should know exist. If a toxin ends up inside your product and someone dies, you cannot simply point at the poisoner and walk away.