Kirkland Signature Sleep Aid Tablets active ingredient is Doxylamine Succinate 25mg, an antihistamine, that maybe used as a sleep aid by adults and children 12 years and older. Kirkland Signature Sleep Aid Tablets are an easy to swallow medication that helps to reduce difficulty in falling asleep. Sleeplessness can be a result of many things. Stress, being "plugged in" to technology, and even being too active can leave you staring at the ceiling at night.