Creating a Facebook page for your business is easy and more importantly, free. So why would you want to pay money to Facebook to promote it?
The short answer is, users don't see everything that could be in their news feed. According to Social Media Examiner, about 10-16% of a page's fans see any given post. Each person's feed is created based on things they like and click, who they're connected with, how they interact with posts in their feed, and the "weight" Facebook gives certain posts. By using Facebook Ads, you're able to push your page and posts into more news feeds, giving you more exposure and more possibilities for likes and fans, in other words, giving your posts or your page a greater "weight."
Facebook also allows you to target specific audiences for your ads. This means you can advertise specifically to those who will be most likely to like your page and visit your pharmacy.