Which supplements or medications are best not combined with NAD+?

The most direct warning applies to cancer patients receiving platinum-based chemotherapy (cisplatin): nicotinamide, a widely used NAD+ building block, can form a chemical compound with cisplatin. This reduces the amount of active platinum available to kill cancer cells. This has been observed in cell studies, not in humans, but the mechanism is specific enough to take seriously. Always discuss the use of NAD+ supplements with your oncologist if you are undergoing platinum-based chemotherapy.

A second, more subtle tension lies in nicotinamide itself. As an NAD+ building block, it supplies NAD+. But at high doses, nicotinamide simultaneously inhibits the enzyme SIRT1, which in turn needs NAD+ to function properly. That enzyme helps regulate oxidative stress. At excessively high doses of nicotinamide, that protective effect can therefore be lost, increasing free radical activity and inflammation. This has been demonstrated in cell studies, not in clinical research in humans.

Experimental cancer drugs that block NAD+ production (NAMPT inhibitors) cause dangerous platelet shortages. Nicotinic acid (niacin, another form of vitamin B3) can partially offset that damage via an alternative pathway. This shows that the NAD+ pathway is sensitive to disruption by medications and that B3 variants can interfere with one another.

Popular supplements such as quercetin, genistein, Ginkgo Biloba, soy isoflavones and milk thistle contain plant compounds that inhibit or activate liver enzymes. Those enzymes also break down many medications. Anyone combining NAD+ supplements with other substances that run through the same liver pathways risks having the effect of those medications strengthened or weakened. This is a broad interaction risk, not specific to NAD+, but relevant if you are taking multiple supplements or medications at the same time.

Sulforaphane (broccoli sprout extract) and fucoidan (a seaweed supplement) disrupt similar liver pathways. Sulforaphane clashed in cell studies with common medications such as the diuretic furosemide, the heart medication verapamil and the painkiller ketoprofen. Fucoidan inhibited liver enzymes in laboratory research. The evidence for this is limited and does not come from studies in humans, but the message is clear: even 'natural' supplements can unexpectedly interfere with medications.