Pfizer (PFE 6.69%) stock was trading 3.6% higher as of 12:01 p.m. Pfizer apparently didn't like the sound of that, so it decided to go the voluntary route. So there's upside for Pfizer in Tuesday's news, alongside the obvious downside that charging less for those medications will result in slimmer profit margins. Is Pfizer stock a buy? Priced at just 12.6 times trailing earnings and an even cheaper-sounding 10.9 times free cash flow, Pfizer stock looks very cheap if the company can achieve any profit growth at all.