"Not only has Amazon finally made a solid move into pharmacy, it has done so via an innovative supplier which helps patients manage and organize their prescription drugs", Saunders said in a research note.
Walgreens' chief executive, Stefano Pessina, said he was "not particularly worried" about the PillPack deal in an earnings conference call with analysts on Thursday, describing it only as a "declaration of intent" by Amazon.
PillPack, which delivers medications in pre-sorted dose packages and employs more than 700, also has offices in Manchester, N.H. The company had previously been rumored to have been in talks with Walmart.
It also coordinates refills and renewals, and makes sure shipments are sent on time.
PillPack was founded in 2013 and had a reported valuation of about $330 million as of two years ago, according to Fortune.
"Together with Amazon, we are eager to continue working with partners across the health care industry to help people throughout the USA who can benefit from a better pharmacy experience", PillPack chief executive TJ Parker said in a statement.
"PillPack's visionary team has a combination of deep pharmacy experience and a focus on technology", Jeff Wilke, Amazon CEO for Worldwide Consumer, said in a statement.
But the prospect of major retailers like Amazon getting into the business has roiled the traditional pharmacy world even further. "We're excited to see what we can do together on behalf of customers over time".
PillPack, which launched in 2014, is available in every USA state except Hawaii.
The deal comes as the health care industry is undergoing a series of convulsions in response to rising costs and pressure on drug makers, pharmacy benefit managers, and insurers.
The deal is expected to close during the second half of 2018.
Of course, Amazon is in the midst of developing a joint healthcare venture in partnership with the CEOs of Berkshire Hathaway and JP Morgan Chase. Startups like San Francisco-based Nimble Pharmacy, which recently expanded to Seattle, are also taking a swing at the space.