The Leap Years supplement lists no known interactions with other medications or supplements, and they report no adverse effects in dogs receiving 10 times the daily dosage. Adverse effects were seen in dogs during their clinical study, but many of these were also seen in the placebo group. More testing is needed.The Leap Years supplement lists no known interactions with other medications or supplements, and they report no adverse effects in dogs receiving 10 times the daily dosage. Adverse effects were seen in dogs during their clinical study, but many of these were also seen in the placebo group. More testing is needed.