A sedative or hypnotic that is the active ingredient in NyQuil, as well as a number of other sleep aids. It is the second most popular over-the-counter sleep aid, after dipenhydramine (Benadryl.) A normal dose is 25mg, with larger doses ranging up to 50mg. Larger doses than that are not recommended. It is also an antihistamine, the most effective sold over-the counter (It shares its antihistamine properties with dipenhydramine.)
Hypnotic effects are felt within fifteen to thirty minutes, though they can be countered by strenuous exercise if only the anti-allergy properties are desired. Allergy relief is felt after the effects of the allergies wear off, taking anything from fifteen minutes to one hour.
It can be habit-forming, so do not use for more than a few days at a time. If you have constant insomnia, this may be indicative of further problems. If you experience serious side effects, stop taking it and ask your doctor.
Personal notes:
Ugh. Do not take unless you really, really need it. It works extremely well as a hypnotic, though I've never used it for allergy relief. The problem, however, is that you wake up and feel worse than you would have if you had simply missed sleep entirely. It also tastes worse than you could imagine - something like essence of lemon mixed with pure caffeine; this makes it difficult to swallow.
It was, for me, much more effective than dipenhydramine for relieving insomnia. If you absolutely must get sleep, I'd recommend it. It runs about $9 for a 32-caplet pack, which should last at least a few months (I've been using it about once every week and a half, so it should last me a year)
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