Positives

• A patient with Long COVID following a 9-medication protocol from a clinic in Birmingham, Alabama, found that antihistamines resolved their headache and dizziness, with slight improvement in brain fog and better sinus health Mayo Clinic Connect.
  
  
• One individual with a chronic condition and suspected MCAS reported “sleeping longer and better” after starting antihistamines, attributing overall symptom improvement to enhanced sleep and relaxation Mayo Clinic Connect.
  
  
• A patient with MCAS experienced a significant reduction in fatigue and joint pain, along with neurological improvements and increased energy, after taking antihistamines Mayo Clinic Connect.
  
  
• A long-term user of antihistamines for cutaneous mastocytosis reported that H1 and H2 blockers controlled their symptoms for decades on a stable daily combination Mayo Clinic Connect.
• A Long COVID patient reported significant improvement in their day-to-day symptoms after starting an H1+H2 antihistamine combination, calling it one of the more impactful pieces of their recovery so far Mayo Clinic Connect.

Negatives

• A patient taking ketotifen, an antihistamine, found it did not reduce their day-to-day symptoms of fatigue and headaches, although it did lessen the frequency of post-exertional relapses Mayo Clinic Connect.
  
  
• Another person experienced worsened dizziness from antihistamines, a side effect that did not improve over time, despite benefits for MCAS and sleep Mayo Clinic Connect.
  
  
• A patient with urticaria reported that their symptoms were unresponsive to various antihistamines, including Benadryl and Zyrtec, indicating limited effectiveness for their condition Mayo Clinic Connect.
  
  

Hurdles & Side Effects

• Several patients reported drowsiness and extreme sleepiness as common antihistamine side effects, with some saying they could no longer drive or work after their morning dose Mayo Clinic Connect.
• Concerns about long-term antihistamine use include potential risks such as choline deficiency, which has been linked to future dementia risk Mayo Clinic Connect.