Multivitamins going bad

During Black Friday, my local reptile store was having a sale on all supplies. I picked up some multivitamins and I have a strong suspicion that they've "expired". I don't think they can expire, I think they just break down and lose nutritional value but the one I got has a strong odor. The best way I can describe it is if rancid wasn't pungent and more bold. Most multivitamins I've seen also are a white powder, this one has an off yellow color to it. It's RepPro Vitamax. The bottle is obviously old since when I opened the packaging the label's glue was completely dried up and lost all stickiness. I was curious if anyone has used RepPro Vitamax and knew if it was simply just a strong odored, yellowed powder and all my senses to tell if a food has gone bad are just wrong in this situation. I would take a picture but my phone camera doesn't pick up the yellow color.

I think they definitely have a best by date , especially once opened and the contents has contact with oxygen in the air.

If in doubt …. best place for the stuff is in the bin , I guess you can't return it for a refund since you've opened the bottle …. (can here (in Australia) but you don't have the same consumer protections in the USA so I guess it's buyer beware and tough luck if you've been diddled).

I am only reading this now, but the multivitamin powder I use (Repcal) also has a yellowish color. Smells terrible too, and it's a bit 'clumpier' than the smoother (and odorless) calcium powder. It almost has a flour-like texture to it.

I would just check the expiration date on the bottle.