U.S. pharmaceutical giant Pfizer announced Monday it would be combining with its Irish rival Allergan, forming the largest health care merger in the history of the industry.

CNN Money reports Pfizer and Allergan's $160 billion agreement will create the largest drug company in the world. The massive merger is the second largest of all time, behind a 1999 merger of two telecommunications firms.

The deal is expected to close by 2016 and predicted to have a $25 billion cash flow by the start of 2018.

According to USA Today, the companies will form under Allergan plc, granting Pfizer freedom from U.S. Treasury rules. Though Dublin-based Allergan is technically the buyer in the merger, Pfizer will lead the combined company.

Pfizer CEO and Chairman Ian Read will retain his titles, while the new company's board will hold all eleven of Pfizer's current directors, in addition to four directors from Allergan. The Allergan plc will also be renamed to Pfizer.

"The proposed combination of Pfizer and Allergan will create a leading global pharmaceutical company with the strength to research, discover and deliver more medicines and therapies to more people around the world," Read said in a news release Monday.

The merger is likely to come under political scrutiny, viewed as a strategic attempt by Pfizer to avoid federal corporate taxes. The Obama administration has criticized these technically legal tax inversions and has sought to implement new rules to restrict the practice.

Despite the controversy, the deal will likely not result in price hikes on drugs. CNN notes that past pharmaceutical mergers have not resulted in significant changes in drug costs. This is great news for the many U.S. citizens who have benefited from Pfizer's assistance programs in the past.

Pfizer Rx Pathways, previously known as Pfizer Helpful Answers, provides uninsured and under-insured Americans with access to free or affordable Pfizer medicines. The service particularly helps to support Latino Americans, who remain the group most likely to be uninsured, with more than 40 percent of Latinos going without health insurance in 2011.

In 2011, 99 percent of medicines provided by Pfizer Helpful Answers were free. It's unknown how this merger will affect the program going forward.

Pfizer is known for providing drugs such as Lyrica, Enbrel and Viagra. Allergan is best known as the maker of Botox.