Fatty Acids

• Omega-3 fatty acids, found in fish oil, can reduce the effects of histamine on your cat, according to PetEducation.com. Fish oil capsules may ease your cat's allergies when administered over a few weeks.
  
  

Biotin

• Biotin may ease your cat's dry skin and itchiness. PetEducation.com notes this B vitamin can be found in capsules or as part of a brewer's yeast supplement.
  
  

Antihistamines

• Antihistamines such as Benadryl and Chlor-Trimeton have a 70 percent effectiveness rate in easing a cat's allergy symptoms, according to PetEducation.com. These capsules should be administered with a veterinarian's guidance, as each comes with a risk of side effects.
  
  

Costicosteroids

• Costicosteroids are sometimes used as a last line of defense in the battle against a cat's allergies. These powerful drugs are highly effective, but come with a high risk of side effects, such as diarrhea and hyperactivity.
  
  

Alternatives

• If your cat resists taking capsules, topical allergy treatments are also available.