Foxglove is entirely natural, and it's also the source of a compound powerful enough to stop a heart at the wrong dose. This guide answers the most common questions about documented supplement risk, synthesized from the reporting in The Hollow Aisle.
No — and the regulatory record makes the point concretely. Ephedra, an entirely natural botanical stimulant, was linked to a documented pattern of cardiovascular events serious enough that the FDA banned it from supplements in 2004, the only time the agency has removed an entire ingredient category this way. Comfrey, with centuries of traditional use, can cause serious liver injury. Aristolochic acid, found in some traditional botanical preparations, has been linked to kidney failure and certain cancers.
"Nature produces both medicines and poisons. 'Natural' is not a safety test."The Hollow Aisle
More than the visible record suggests, and researchers describe the visible record itself as an undercount. Between 2004 and 2021, the FDA's adverse event system received more than 79,000 reports tied to dietary supplements. A widely cited analysis of the 2004–2013 window alone found more than 15,000 reports that included 339 deaths and nearly 4,000 hospitalizations.
The Drug-Induced Liver Injury Network (DILIN), an NIH-funded research consortium, found the share of documented liver injury cases attributed to herbal and dietary supplements rose from 7 percent to 20 percent between 2004 and 2013 — a statistically significant increase. Liver injury linked to bodybuilding supplements produced no deaths or transplants in the study population; liver injury linked to non-bodybuilding supplements, taken predominantly by middle-aged women, was significantly more severe.
Yes. The same DILIN research found that of 73 products implicated in green tea extract-linked liver injury, 29 — 40 percent — didn't list green tea extract or its active compounds on the label at all, despite laboratory testing confirming its presence.
In 2000, physicians reported in The Lancet that heart transplant patients taking St. John's Wort for mood support experienced dangerously low levels of cyclosporine — the drug preventing their organ rejection — because the herb induces a liver enzyme system cyclosporine depends on. Several patients experienced acute transplant rejection. St. John's Wort is separately documented to reduce the effectiveness of oral contraceptives and several chemotherapy agents through the same mechanism.
| Supplement | Documented interaction risk |
|---|---|
| Fish oil, high-dose vitamin E, ginkgo | Compound anticoagulant/antiplatelet bleeding risk |
| Chromium, bitter melon, cinnamon | Can compound diabetes medication effects into hypoglycemia |
| St. John's Wort | Reduces immunosuppressant, contraceptive, and chemotherapy effectiveness |
| Melatonin, valerian, kava | Can compound prescribed sedative effects |
Yes. Fat-soluble vitamins (A, D, E, K) accumulate in fatty tissue and the liver, unlike water-soluble vitamins, which are mostly excreted. Iron is essential for preventing anemia and is also one of the leading causes of fatal accidental poisoning in young children. Selenium and zinc correct real deficiencies and cause real toxicity syndromes at chronic excess. The dose makes the poison — for a vitamin exactly as much as for a prescription drug.
Every figure on this page is drawn from the sourced reporting in The Hollow Aisle. See the book for full citations.