Originally Posted by
planemechanic
Acetaminophen max dosage per day is 4,000mg. Each NyQuil capsule has 325mg, so four capsules would give you 1,300mg at one time. Liver damage is generally considered a concern at dosages above 7,000mg, so I think taking a double dose of NyQuil is pretty safe and within the realm of reason.
Some OTC cough medicines (Ny/Dayquil included) also contain DXM, which can be used recreationally for its dissociative and hallucinogenic properties. Medium doses usually require about 400mg or 2.5-7.5mg/kg to achieve this, but some highs can be achieved with as little as 100mg.
Considering that each dose of Nyquil only contains about 30mg of DXM, you'd probably be doing more damage to your liver than getting high off of it, but it's still something to consider.