United states securities and exchange commission

Table of Contents
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The illegal distribution and sale by third parties of counterfeit versions of our products or stolen products could have 
a negative impact on our reputation and business.
Third parties might illegally distribute and sell counterfeit or unfit versions of our products, which do not meet 
our rigorous manufacturing, distribution and testing standards. A patient who receives a counterfeit or unfit drug may 
be at risk for a number of dangerous health consequences. Our reputation and business could suffer harm as a 
result of counterfeit or unfit drugs sold under our brand name. Stolen inventory that is not properly stored or sold 
through unauthorized channels could adversely impact patient safety, our reputation and our business. In addition, 
inventory that is stolen from warehouses, plants or while in-transit, and that is subsequently improperly stored and 
sold through unauthorized channels, could adversely impact patient safety, our reputation and our business.
The increasing use of social media platforms presents new risks and challenges.
Social media is increasingly being used to communicate about our products and the diseases our therapies are 
designed to treat. Social media practices in the biopharmaceutical industry continue to evolve and regulations 
relating to such use are not always clear. This evolution creates uncertainty and risk of noncompliance with 
regulations applicable to our business. For example, patients may use social media channels to comment on the 
effectiveness of a product or to report an alleged adverse event. When such disclosures occur, there is a risk that 
we fail to monitor and comply with applicable adverse event reporting obligations or we may not be able to defend 
the company or the public's legitimate interests in the face of the political and market pressures generated by social 
media due to restrictions on what we may say about our products. There is also a risk of inappropriate disclosure of 
sensitive information or negative or inaccurate posts or comments about us on any social networking website. If any 
of these events were to occur or we otherwise fail to comply with applicable regulations, we could incur liability, face 
overly restrictive regulatory actions or incur other harm to our business.
Some of our collaboration agreements contain change in control provisions that may discourage a third party from 
attempting to acquire us.
Some of our collaboration agreements include change in control provisions that could reduce the potential 
acquisition price an acquirer is willing to pay or discourage a takeover attempt that could be viewed as beneficial to 
shareholders. Upon a change in control, some of these provisions could trigger reduced milestone, profit or royalty 
payments to us or give our collaboration partner rights to terminate our collaboration agreement, acquire operational 
control or force the purchase or sale of the programs that are the subject of the collaboration.  
We may incur operational difficulties or be exposed to claims and liabilities as a result of the spin-off of our 
hemophilia business.
On February 1, 2017, we distributed all of the then outstanding shares of Bioverativ common stock to Biogen 
shareholders in connection with the spin-off of our hemophilia business.  In connection with the distribution, we 
entered into a separation and distribution agreement and various other agreements (including a transition services 
agreement, a tax matters agreement, a manufacturing and supply agreement, an employee matters agreement, an 
intellectual property matters agreement and certain other commercial agreements). These agreements govern the 
separation and distribution and the relationship between us and Bioverativ going forward, including with respect to 
potential tax-related losses associated with the separation and distribution. They also provide for the performance of 
services by each company for the benefit of the other for a period of time (including under the manufacturing and 
supply agreement pursuant to which we will manufacture and supply certain products and materials to Bioverativ).
The spin-off of our hemophilia business as an independent public company is intended to qualify for tax-free 
treatment to Biogen and its shareholders under the Internal Revenue Code. Completion of the spin-off was 
conditioned upon, among other things, our receipt of a favorable opinion from our tax advisors with respect to the 
tax-free nature of the transaction. The opinion is not binding on the U.S. Internal Revenue Service (IRS) or the 
courts, and there can be no assurance that the IRS or the courts will not challenge the qualification of the spin-off 
as a tax-free transaction or that any such challenge would not prevail. If the spin-off is determined to be taxable, the 
full financial benefits expected to result from the separation may not be achieved and/or Biogen and its 
shareholders could incur significant tax liabilities, which could adversely affect our business, financial condition or 
results of operations and the value of our stock could be adversely impacted.
Bioverativ has agreed to indemnify us for certain potential liabilities that may arise, but we cannot guarantee 
that Bioverativ will be able to satisfy its indemnification obligations. The separation and distribution agreement 
provides for indemnification obligations designed to make Bioverativ financially responsible for many liabilities that 
may exist relating to its business activities, whether incurred prior to or after the distribution, including any pending 
or future litigation. It is possible that a court would disregard the allocation agreed to between us and Bioverativ and 

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