Coffee and tea contain methylxanthines, which cause temporary increases in the natural production of vasopressin, a hormone produced by the pituitary gland  Vasopressin causes clumping of blood cells, and the clumping is more pronounced in women than in men
This is probably the explanation of the fact that women face as much as a tenfold higher risk than men do of complications following angioplasty, a technique used to clear clogged arteries
Men, but not women, should be given methylxanthines prior to undergoing angioplasty.