I think you're right on.
Most drugs are chemical compounds mixed up with some inactive elements that are delivered in a state of high chemical purity and with a standardized dose. There are many forms for delivering drugs -- topical creams and ointments, oral suspensions and tablets and elixirs and capsules, intravenous solutions, intradermal, suppository, inhaled, etc, etc. We have reasonably good pharmacokinetic
data for drugs that have undergone review and approval by the FDA. Pharmacokinetics is the study of what the body does to the drug, how the drug chemically changes, where it distributes in the body, how the drug levels change over time, etc. For example, I know not to use certain antibiotics for meningitis because they don't distribute into the central nervous system. We also have good pharmacodynamic
data for approved drugs -- we know what effect they achieve, and in many cases their molecular site of activity and how the drug compound chemically interacts with its target. We also have data about adverse events.
When we look at herbal supplements, which have claims
of health benefit, we don't have very much (if any) of the above information. Do we know what a safe dose of onion extract is? Does onion extract interact with other drugs? Does it actually
have a health benefit? Are there side effects?
herbal supplements and dietary components are beneficial. I think eating omega-3 fatty acids certainly has some benefit, at least for cognitive development in newborns. Having high fruit/veggie diets are associated with lower risk of cardiovascular diseases. But without rigorous studies we also have a lot of speculation and even some quackery out there. People STILL take megadoses of vitamin C because Linus Pauling was promoting it 50+ years ago, despite no evidence that it helps with colds. People STILL rave about antioxidants even though there is no evidence that they are beneficial (and vitamin E has been completely debunked as helpful for heart disease). So even if there is no harm, should people be wasting their money and energy on something that isn't helpful? Should people be taking something harmless in lieu of something that actually works?