how long nyquil kicks in
How Long Does It take For Nyquil To Kick In ? How Long Does Nyquil Last? As per the guidelines provided by its manufacturer Vicks, the effect of Nyquil last up to 8 hours. But beware, depending on how much you are sensitive to the sedating properties, this duration may get extended little longer. 6 hours, 8 hours, 10 hours, no matter how many hours you sleep, you would still feel heavy and drowsy for the next few hours.