POWER OF ATTORNEY


I, the undersigned, a director and/or an
executive officer of Biogen Idec Inc., hereby authorize and designate
Thomas J. Bucknum, Anne Marie Cook, Jo Ann Taormina, and Benjamin S.
Harshbarger and each of them acting alone, as my attorney-in-fact to
execute and file on my behalf any and all Forms 3, 4 and 5 (including any
amendments thereto) that I may be required to file with the United States
Securities and Exchange Commission as a result of my ownership of or
transactions in securities of Biogen Idec Inc.  The authority granted under
this power of attorney shall continue for so long as I am required to file
Forms 3, 4 and 5 with regard to my ownership of or transactions in
securities of Biogen Idec Inc., unless earlier revoked in writing, but
shall terminate automatically as to each individual attorney-in-fact when
such person is no longer an employee of Biogen Idec Inc.  I acknowledge
that the attorneys-in-fact appointed hereunder are not assuming, nor is
Biogen Idec Inc. assuming, any of my responsibility to comply with Section
16 of the Securities Exchange Act of 1934.

	IN WITNESS WHEREOF, the
undersigned has caused this instrument to be duly executed this 25th day of
January, 2004.


						/s/ Burt A. Adelman

						Burt A.
Adelaman