Is it a good source of NIACIN?
That depends on how you brew it. This episode has the details on the effect of roasting, coffee strength, and decaffeination.
Here’s a massive 2-part podcast series I did on niacin with Alex Leaf, which has 52 scientific references:
Here are other recent episodes on niacin:
Should You Inject Yourself With NAD+?
The Best Form of Niacin for Anti-Aging