This is the piece the rest of the section exists for. Most people who substitute a supplement for a prescription are not making a philosophical choice about medicine. They are making a financial one.
People really do skip prescriptions over price
The CDC's National Center for Health Statistics has measured the strategies American adults use to reduce what they spend on prescriptions: skipping doses, taking less than prescribed, delaying a fill, and asking a doctor for a cheaper alternative. Millions of adults report doing at least one of them. It is not a fringe behaviour and it is not irrational — it is what happens when a price is genuinely out of reach.
The supplement aisle is where a good number of those people go next, because it is the nearest thing that looks like a substitute and does not require a prescription.
The arithmetic usually goes the other way
Supplements are priced as consumer products. They carry branding, packaging and marketing, and none of the competitive pressure that pushes a generic down once several manufacturers make it. A month of a branded herbal preparation frequently costs more than a month of the generic drug it is standing in for.
Many of the most widely prescribed generics — metformin, lisinopril, atorvastatin, levothyroxine — cost a few dollars a month at the right pharmacy. People routinely do not know this, because the number they were quoted at one counter was much higher, and one quote is what most people have.
What to do instead, if price is the barrier
Price the drug first, at the quantity you actually fill. If the number is small, the decision makes itself. If it is not, there are three routes that all beat a supplement on both cost and evidence: a different pharmacy, mail order, and manufacturer assistance programmes, which cover many uninsured people at no cost and are checked from the price page.
And if you are going to take a supplement anyway — which is a legitimate choice to make with your own money — read what is actually in the bottle first, and tell a pharmacist you are taking it.