For the same reason, it is typically recommended that nursing mothers not use medication containing bismuth subsalicylate because small amounts of the medication are excreted in human breast milk, and these pose a theoretical risk of Reyes syndrome to nursing children.Salicylates are very toxic to cats, and thus bismuth subsalicylate should not be administered to cats.The British National Formulary does not recommend bismuth-containing antacids (unless chelated), cautioning that absorbed bismuth can be neurotoxic, causing encephalopathy, and that such antacids tend to be constipating. Drug interactions
There is an increased risk of bleeding when using bismuth subsalicylate and anticoagulation therapy, like Coumadin (Warfarin)

Mechanism of action
Bismuth subsalicylate is used as an antacid and antidiarrheal, and to treat some other gastrointestinal symptoms, such as nausea. The means by which this occurs is still not well documented. It is thought to be some combination of the following:
Stimulation of absorption of fluids and electrolytes by the intestinal wall (antisecretory action)
As a salicylate, reducing inflammation/irritation of stomach and intestinal lining through inhibition of prostaglandin G/H synthase 1/2
Reduction in hypermotility of the stomach
Inhibits adhesion and filmogenesis by Escherichia coli
Bactericidal action of a number of its subcomponents, including salicylic acid
Bactericidal action via a so-called oligodynamic effect in which small amounts of heavy metals such as bismuth damage many different bacteria species. Weak antacid propertiesIn vitro and in vivo data have shown that bismuth subsalicylate hydrolyzes in the gut to bismuth oxychloride and salicylic acid and less commonly bismuth hydroxide. In the stomach, this is likely an acid-catalyzed hydrolysis.
Bismuth subsalicylate, sold generically as pink bismuth and under the brand names Pepto-Bismol and BisBacter, is an antacid elixir medication used to treat temporary discomforts of the stomach and gastrointestinal tract, such as nausea, heartburn, indigestion, upset stomach, and diarrhea. Bismuth subsalicylate has the empirical chemical formula of C7H5BiO4, and it is a colloidal substance obtained by hydrolysis of bismuth salicylate (Bi(C6H4(OH)CO2)3). Medical uses
As a derivative of salicylic acid, bismuth subsalicylate displays anti-inflammatory and bactericidal action. It also acts as an antacid. Adverse effects
There are some adverse effects. It can cause a black tongue and black stools in some users of the drug when it combines with trace amounts of sulfur in saliva and the colon to form bismuth sulfide. Bismuth sulfide is a highly insoluble black salt, and the discoloration seen is temporary and harmless. Long-term use (greater than six weeks) may lead to accumulation and toxicity. Some of the risks of salicylism can apply to the use of bismuth subsalicylate.Children should not take medication with bismuth subsalicylate while recovering from influenza or chicken pox, as epidemiologic evidence points to an association between the use of salicylate-containing medications during certain viral infections and the onset of Reye syndrome.