Positives

• A long-hauler managing mast cell activation syndrome reported that completing their H1/H2 antihistamine protocol by adding cimetidine as the H2 component “helped stop the mast cell attacks,” noting the dual-blocker approach was more effective than their H1 antihistamine had been alone Reddit.
  
  

Negatives

• One patient who had been prescribed multiple H2 blockers including cimetidine noted that the medication alone was not sufficient to control their symptoms without also following a strict low-histamine diet Reddit.
  
  

Hurdles & Side Effects

• One patient managing MCAS found that cimetidine’s effects on liver enzyme pathways meant their doctor had to review their full medication list before they could start it, adding a coordination step that delayed access to the treatment Reddit.