D.B.
Does it work for what? Do you have a specific issue or goal? Usually single-ingredient treatments aren't that beneficial long term, and they can throw off a lot of systems. I agree with Mel R. about quality supplements - you really have to know where they are made. Fully 1/3 of "all natural" products found in high end stores, where you'd think the quality might be better, were found not to contain what the label said they did. If something has a patent (on the whole product, not just one ingredient), then the label is accurate, but patents are hard to find especially in over-the-counter products. Some supplements carry warning labels (same with most vitamins) as required by the FDA, but others are metabolized as food and don't require warnings - but that doesn't always mean quality.
So if it has a warning, consult your physician. If it doesn't, and it's a food product, your physician may not be particularly schooled in nutrition (most aren't).
But most food scientists (who deal in nutrition far more) don't see much value in individual nutrients - that's not how the body utilizes vitamins & minerals and so on.
Essential oils are a big fad right now but a lot of the companies have been sanctioned by the FDA for making health claims for cures and treatments, which is false.