Positives

• An MCAS patient rotating H1/H2 blockers including Tavist reported reduced dizziness, itchiness, and nausea on the regimen Inspire.
  
  
• A long-term user reported using clemastine for years for allergies and hay fever with effective relief and no noticeable side effects Drugs.com.
  
  

Negatives

• Many patients reported transient drowsiness as the most common reaction, with some experiencing dizziness and disturbed coordination Drugs.com.
  
  
• One MCAS forum participant felt Tavist was not as popular or as effective as other first-generation antihistamines Inspire.
  
  

Hurdles & Side Effects

• Patients found clemastine impaired thinking and reactions enough that driving and tasks requiring alertness had to be avoided after dosing Drugs.com.
  
  
• Some patients had to push through an initial week of sleepiness before tolerance built and the daytime sedation became manageable Drugs.com.