<p>Some prescribing information records the protein binding of diphenhydramine as approximately 78% <sup class="text-reference-group"><a class="reference-popover-link" data-content="Benylin Chesty Coughs UK MHRA Product Information" href="#reference-F3394">18</a></sup> while others have suggested the medication is about 80 to 85% <sup class="text-reference-group"><a class="reference-popover-link" data-content="Electronic Medicines Compendium: Nytol One-A-Night (diphenhydramine hydrochloride) Monograph" href="#reference-L5287">13</a></sup> bound to plasma proteins.</p>