Doctors weigh in on vitamins and supplements, and the message is mixed news depending on how you shop and what else you're taking.

• Most supplements aren't regulated like medications, so labels can be inaccurate or contain impurities — look for third-party seals like USP or NSF for trustworthy products.
• A basic multivitamin is a reasonable choice for most people to fill gaps in an imperfect diet, and cheaper store-brand versions work fine as long as they cover close to 100% of daily recommended amounts.
• Supplements can clash with medications: calcium blocks absorption of thyroid medicine if taken too close together, and multivitamins containing vitamin K can cancel out blood thinners like warfarin.
• Doubling up on vitamins (from a multivitamin plus separate pills) can lead to overdoing it, and too much vitamin B6 in particular can cause nerve damage.
• Doctors want patients to disclose every supplement they take, since it affects both drug interactions and unnecessary spending.

Outlook: Expect doctors to keep pushing patients to disclose supplement use and check for interactions rather than avoid supplements altogether.