Complex sentence: This non-sedating antihistamine is sold under the brand name Benadryl Allergy Relief in the United Kingdom by McNeil Laboratories, not to be confused with Benadryl Once a Day, which is cetirizine and is also sold by McNeil in the UK.
Split into simpler sentences: This non-sedating antihistamine is sold under the brand name Benadryl Allergy Relief in the United Kingdom by McNeil Laboratories. It should not be confused with Benadryl Once a Day which has cetirizine as the active ingredient and is also sold by McNeil in the UK.