The basic idea that tiny amounts of substances that harm you in various ways might benefit you in a related way is magical thinking. But when you can't rely on the 'tiny amounts' part, you're in pretty nasty territory.
Come to think of it, the company I work at does process engineering and plant design/construction mainly for companies in the food industry, but we have a a couple of customers from the pharmaceutical industry as well.
And the impression I got so far (being the in-house IT admin, I can only watch it from a distance), is that the pharmaceutical customers are extremely meticulous. And with good reason, of course. Imagine if a batch of paracetamol/acetaminophen tablets contained 5g instead of 0.5g.
But if the engineering and QA at homeopathic companies is as scientific as homeopathy itself, that is not surprising. :(
Vaccines and the entire concept of hormesis is something you should research when you get the chance.