BIIB), Intuitive Surgical ( ISRG) and Humana ( HUM). Thursday's deal may make Express Scripts the largest pharmacy benefits manager in the U.S., controlling 30% of the market. CVS Caremark ( CVS) would be the odd man out, in second place for market share. The $71.36 per-share offer, denominated in both cash and stock, represents a 28% premium to Medco's closing share price, as of yesterday. The premium is warranted, given that the new company would have tremendous synergies, from a cost and growth perspective. Therefore, it is likely to be scrutinized by regulators. The acquisition will help Express Scripts compete in the low-margin business of distributing drugs for insurance companies and employers. Express Scripts posted a first-quarter net margin of 2.9% and Medco achieved a spread of around 2%. The catalyst for the deal: Medco has suffered major contract losses as of late, including a partnership with UnitedHealth ( UNH), accounting for as much as $11 billion of sales. The company also lost contracts in March, pressuring the management team to explore strategic options to unlock value for shareholders. The deal announcement marks the second largest of the year, after AT&T ( T) declared its intention to buy T-Mobile USA for $39 billion. Analysts are offering positive reviews, so far, while stressing that anti-trust regulators will thoroughly weight the benefits and costs of the deal for consumers, the industry and shareholders. Health care has been hot in 2011. Express Scripts shares have rallied 24% in the past 12 months and Medco's have appreciated 21%. Equity researcher Leerink Swann expects the deal to increase Express Scripts' earnings, citing $1 billion of synergies. Leerink Swann views the deal as "a significant positive for both companies." Bank of America went further than Leerink Swann by saying that "estimated synergies of $1 billion seem conservative." The pharmacy benefits business depends on scale and bargaining power, which will be vastly amplified by the deal.