I have known for many years that I had an allergic reaction to 20mg Benadryl, whenever I took it to counteract my other allergies. The reaction was the sensation that my veins in my left leg were being squeezed and this would go on for 30-45mins and when it stopped my entire foot would ache and though it didn t, I would have expected my foot to look black from lack of blood. This happened every time I took Benadryl. So, my allergist told me to use 10mg Loratadine. I did this for several years with no problem. Then, one night, I was having an allergic reaction and I thought 24hrs had passed so I took another one and I had the same reaction that I`d had with Benadryl-exactly the same! In other words, I get this allergic reaction from 20mgs of an antihistamine, which, by the way is the only dosage amount that is effective for me-10mgs does nothing. I told my allergist, he said I m between a rock and a hard place. I hope you can please give me a better answer. Thank you.