A pharmacist checks this free.

Because a clean result would be the dangerous outcome — it reads as clearance when it's only silence. There are concrete reasons too: nothing here can see your actual products, and supplement labelling isn't reliable in the way medicine labelling is, with products found to contain different amounts than stated, undeclared ingredients and sometimes pharmaceutical adulterants. Interaction databases are also maintained continuously by professionals, while anything generated from training data is a snapshot.

A pharmacist, and this is the most useful fact in the whole guide. In most countries they can be spoken to without an appointment and at no cost, they hold the maintained databases, and they do this daily — yet almost nobody thinks to ask them about supplements. The check takes a couple of minutes once they have a complete list, which is the part that usually goes wrong.

Consistently the same five things: medicines taken so long they stop feeling like medicines, occasional painkillers, hormonal contraception, anything applied rather than swallowed, and supplements not thought of as drugs. Teas, tonics, protein powders and fortified foods count too. A check against an incomplete list is worse than no check, because it produces confidence rather than information.

A multivitamin, a single-nutrient supplement and a fortified cereal can each contain the same thing, so totals climb without anyone deciding to. It matters most for fat-soluble vitamins, which accumulate rather than being excreted readily, and for minerals with narrow margins between useful and too much. It's also the one interaction problem you can find yourself, just by reading labels and adding up.

Don't stop a prescribed medicine on your own — stopping abruptly can cause problems of its own, and that decision belongs with a professional. If you've had new symptoms since starting or changing something, raise it promptly rather than researching it, and treat unusual bleeding or bruising, chest pain, severe headache, confusion, yellowing of the skin or eyes, or a rash with swelling as reasons to seek help now.