NASCAR Racing: Sponsor, and drivers obligation, program cars, personal vehicles

Question
Hi, I have a couple of related questions.

First, are drivers obligated to use their sponsors products? (Does Mark Martin have to use Viagra?)

And second, do drivers' personal vehicles have to be the same make as their race cars?

Answer
I don't know what's written into every driver's contract but I doubt they go so far as to demand that the product is used or make of car driven.
BUT, the manufacturers are very free with samples and having their spokesperson seen with their product in hand (or nearby). I'd be willing to bet that many driver's are given program cars or trucks of their make to drive. At the race track the local dealer of the driver's make usually supplies cars for the drivers to drive locally.

So, if it's given to them free for their use, yes, they use the product. But do they have to? No. Will the sponsor find someone else if the driver uses a competitors product? Probably.