Not for long, given who will be running the next administrations FDA, and the general cult of "de-regulation" taking hold.

someone that voted for them would argue that those regulations are what brought us to the current predicament. It’s currently very legal to make addictive unhealthy food

If they do find something that fits the bill, it will be referred to and marketed as “appealing to the cravings of folks on these drugs, and they personally need to be responsible about their choices”.

It’s helpful to remember that this is the same corporate landscape where (in the US) insurance companies can decline prescriptions in order to reduce their own costs.

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.

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.