[bodiekane]

What law would it be breaking?

There are tons of common foods and food additives that are known to interact with medications. Grapefruit juice for instance has a large and diverse set of drug interactions, some potentially very dangerous: https://www.drugs.com/article/grapefruit-drug-interactions.h... but that doesn't mean it's illegal to sell or consume.

[Teever]

The key word is intentional.

If you're intentionally researching and developing an additive that weakens the effect of a prescription medication and you're not telling people the. You're effectively poisoning them.

That's super illegal.