My 3 month old daughter is currently teething. Nightly before bed, she gets some tylenol to ease some of her discomfort. She gets the minimum dose (1ml). Since we started giving her the tylenol nightly, Ive noticed a slight decrease in the effectiveness of her Zantac. Is this a coincidence?

Hi , this is most likely a coincidence. It shouldn't prove to show any repeating pattern.
Thanks, Graham Ph.C.