See below, in one reported extreme case, the reduced blood flow from a DOB overdose (~75 mg or so) forced someone to amputate a leg... I wouldn't want to wake up in a hospital after 75 mg DOB (you are probably high for at least two days) and finding out that I've been amputated...
Vascular Spasms (http://www.vet.purdue.edu/vtdl/tmp/course_work/blood/nutshell/list_items/hemostasis_2.htm)
(http://www.vet.purdue.edu/vtdl/tmp/course_work/blood/nutshell/list_items/hemostasis_2.htm)
Vascular spasms narrow blood vessels (cause vasoconstriction) and reduce blood flow. Spasms are due to the contraction of the smooth muscle of the blood vessels. These contractions result from sympathetic nervous system stimulation and the action of serotinin. Serotinin is a powerful local vasoconstrictor substance released by blood platelets.
Both DOB and DOM has always been phenethylamines (alpha-methyl-phenethylamines to be exact), and the Shulgin quote in Barium's post above comes from Pihkal #62 (DOB) (http://www.erowid.org/library/books_online/pihkal/pihkal062.shtml)
(http://www.erowid.org/library/books_online/pihkal/pihkal062.shtml).