I don't think it's proven that the tick need to be on you all that long, it seems to be a theory that they have to be on you for 12 hours to get lime but that doesnt make any sence to me. Iv'e had it twice and I'm pretty sure I got the ticks off immediatly. That being said I take plenty of other medicin, It's gotta be safer than some of the stuff ticks will give ya.