Not everyone can conquer sleeplessness by staying awake, counting sheep, or trying to slip into a daydream. Some people (like me) have chronic insomnia, which makes it easy to chuckle at conventional methods of getting to sleep, especially after months or years of trying. Thus, there is only a single avenue to dreamland worth mentioning: drugs.
A slight caveat to this writeup is that it is mostly aimed at insomniacs in the USA, as I have no experience with the drugs available in other countries.
However, before you go skipping off to the pharmacy, there is a process of elimination that you should go through to make sure some other factor isn't causing your insomnia. You should see a general practitioner, psychiatrist, or sleep specialist to make sure none of the following are the root of the problem:
There are a host of other possibilities, but these seem to be the most common. They can all be treated with non-sedative drugs, hypnosis, or whatever other method of healing you think works for you.
If none of the above are the cause of your insomnia, then there is a middling range of effective sedative drugs available, some over-the-counter, some prescription.
Over-the-counter sedatives:
Dextromethorphan (DXM) — the primary ingredient in NyQuil and a lot of other cold/flu medicines. It is a disassociative (and a decongestant), so caution should be exercised when taking large doses. Sedative doses start at 15mg. In low doses, I find that it doesn't have much in the way of sedative effects at all. However, if I take double or triple the normal sedative dose (which works out to 60-75mg), it works as advertised, though I have to take it straight — no other drugs included, so NyQuil is out of the question due to the acetominaphen it contains and the risk of acetominaphen-borne liver failure; I take two or three 30mg tablets of DexAlone¹, which is pure DXM, and in tablet form it is much easier to consume than Vicks Formula 44 or other DXM-only liquid suspensions (though they are the same drug, just in different forms). This might just be a factor of my metabolism, though, so try lower doses first. Too many brand names to list. (This stuff is not OTC in a number of countries, although it can prescribed by doctors in such places.)
Diphenhydramine hydrochloride or citrate — both have about the same effect. Some people are more receptive to this than others. A common sedative dose is 50mg. Be careful at doses higher than 50mg, however, as they can cause some pretty unpleasant hallucinations, among other nasty effects, as diphenhydramine is a disassociative. Brand names: Benadryl, Tylenol PM, and others.
Doxylamine succinate — an antihistamine, which, by definition, attempts to gradually shut the body's more acute senses down to a level where sleep can be achieved. This stuff, however, doesn't make me sleepy, as such; but if I take some before bed, I'll feel its sedative effects after waking up (which defeats the purpose of a sedative). Sedative doses range from 5mg to 40mg. Brand names: Unisom, Sominex, and others. It is also included in NyQuil and DayQuil in small doses.
Melatonin — the human brain produces melatonin when it gets dark outside, to help regulate your circadian rhythm. Synthesized melatonin is what you'll find in stores, and it is best when used by people who work at night and sleep when the sun is up. Not really a sedative, but it helps some people get to sleep. Common doses are 1mg to 20mg. Most chain pharmacies carry their own branded melatonin, and most herbal supplement manufacturers produce it as well. So far, I've found California Health's "extended release" 10mg formula to be most effective.
Valerian root — a herb which makes restfulness easier to achieve for some people. It smells extremely pungent (and the smell stench will make cats go completely out of their gourds, moreso than catnip, so beware of using this stuff in a cat's presence), so much so that some people are unable to take it because it tastes like it smells — awful. I've found that this stuff works pretty well when combined with melatonin or any of the other drugs listed above (as long as I don't inhale when the pills are in my mouth, that is). It's sold mostly in doses of 450mg per capsul or tablet.
Prescription sedatives:
Barbiturates — the market for these has sunk like a stone since more effective and less dangerous drugs have been developed, as these are easy to overdose on. The only one I've ever been prescribed is Fioricet (butalbital), which is used for treating tension headaches. Doses are typically 40mg per pill, taken as necessary. The effect Fioricet had on me was a gradual slowing-down of the body until sleep seemed irresistable, despite the presence of caffeine in the pill. Fioricet is sometimes combined with codeine. Another barbiturate, Seconal (secobarbital), was the most-prescribed sedative in the USA until the introduction of Valium (diazepam) in the 1970s. Officially, the primary use of these drugs is to prevent seizures. It should also be noted that barbiturates are commonly sold on the street as "reds."
Benzodiazepines — this includes Ativan (lorazepam), Klonopin (clonazepam), Valium (diazepam), and Xanax (alprazolam), among many others. Doses vary according to which drug in particular is being taken, though Valium and Xanax are (in my experience) the strongest. 2mg of Xanax is enough to knock most people out for about 12 hours. Any of these drugs, when combined with alcohol, produce muscle weariness, general disorientation, severely reduced coordination, euphoria and eventually, deep sleep. Generally these are prescribed as anti-convulsant drugs, and are meant to prevent panic attacks, nervous tics, and various other mentally-triggered physical disorders.
Muscle relaxants — including Flexeril (cyclobenzaprine hydrochloride), Robaxin (methocarbamol), Skelaxin (metaxalone) and Soma (carisoprodol), among others. These are the most effective for bodies that have a really hard time becoming tired. Flexeril doses generally start at 5mg, Robaxin at 500mg, Skelaxin at 400mg, and Soma at 1mg. When combined with other drugs, such as benzodiazepines, they tend to numb the mind as well as the body, making it easy to get to sleep. Often they're combined with narcotic painkillers such as Vicodin (hydrocodone and APAP), as well, which provides more of a body-high than sleepiness.
Non-benzodiazepine hypnotics (imidazopyridines and cyclopryrrolones) — this class of drugs includes Ambien (zolpidem tartrate; aka Stilnox), which is probably the most effective sedative you can get outside of a hospital; Sonata (zaleplon), a reduced-strength version of Ambien; and Halcion (triazolam, officially a benzodiazepine, but it's not used as one), which is often used in dental surgery to make a patient "forget" about the pain. Doses for Ambien start at 10mg, Sonata at 5mg, Halcion at 0.5mg. It is necessary to take these drugs immediately before going to bed (or into surgery), especially with Ambien, else you'll most likely wind up in an Ambien stupor, which is like being drunk only with infinitely worse judgement capabilities. There are about a dozen of these drugs, though these three are by far the most common, and the others are mostly used in hospitals (with the exception of trazedone, which is infrequently prescribed). Two new drugs in this class, Sanofi-Aventis' Ambien CR (zolpidem extended release) was released in 2006, and Sepracor's new anti-insomnia drug Lunesta (eszopiclone; known as Imovane in every country where chemicals are branded and sold as medication, but not in the USA—in countries that don't brand their medicines, it's known as zopiclone) was approved by the FDA in 2004, after sixteen years of development and refinement, and became available to the public in May 2005. Pfizer's new sedative, Indiplon, may make its debut around that time, too, although problems with the US FDA have postponed its release many times over the past five years. In 2007, the drug Rozerem (ramelteon) was introduced. According to its commercials, website, etc., it binds to melatonin receptors in the brain rather than the standard GABA receptors that almost all other sedatives bind to. I haven't tried it yet, so I can't recommend it one way or the other. One could also include promethazine in this group, though it's actually an antihistamine. It's a strong anti-nauseant frequently prescribed to sufferers of migraine headaches. It has strong sedative properties, but it's rarely prescribed as a sedative. In most of the English-speaking world, it's available over the counter, but in the USA, it's prescription-only.
Antipsychotics — Many antipsychotic drugs contain sedative elements; everyone's heard of the thorazine shuffle, but that's going a bit off the deep end, so to speak. For less troubled insomniacs, there's Seroquel (quetiapine). Although its main purpose is to keep its users from shooting up the local post office, it has, in recent years, seen increasing use by insomniacs, at low doses, typically 50-200mg (in comparison, a schizophreniac will take 400-800mg per day). A number of psychiatrists and psychologists have been prescribing it to the sane, for help getting to sleep. (This is known as "off-label" use.) By itself or when combined with Ambien, Lunesta or Sonata, works like a charm for quite a few people. The crutch here is that you have to be seeing a shrink to get a prescription for it, although, apparently, you needn't be tripped out of your gourd.
I've found that taking a non-sedative antihistamine, such as loratadine (generic Claritin, which is one of the "new" non-drowsy antihistamines), along with any of the narcotic or controlled drugs listed above can lend a slight increase in the effectiveness of the sedative effects of your chosen drug(s). YMMV, of course. (A similar effect is produced when you combine 25-50mg of diphenhydramine, which is an "old guard" antihistamine, and an opiate painkiller; the diphenhydramine, if consumed about half an hour before the painkiller, makes the body's natural opiate receptors more receptive to opiates.)
Granted, any of these drugs could have virtually any effect on anyone (though the risk of allergies to most of these—other than valerian root—is virtually nil, the risk of addiction is high), so be sure to talk to your doctor about them before accepting a prescription. If you've exhausted all the other options for trying to get to sleep, you might want to give them a try. Some people, after taking sedatives for however long a time, have no further problems sleeping after coming off the drug(s). Others feel the need to take them for years or even a lifetime. Whatever the case, drugs are a much-maligned way around insomnia. Despite their bad reputation, they do a lot of people a lot of good, as many are simply unable to get to sleep, even after staying awake for days on end. The regulation of sleep by insomniacs is frequently misunderstood by those who aren't insomniacs, hence their bad reputation. Using them isn't a guaranteed cure, but they're certainly better than nothing, or worse, no sleep at all.
I am not a doctor, so please consult with one if you feel the time is right for drug-regulated sleep.
Update: I discovered the use of medical cannabis for treatment of insomnia in 2014 and I haven't bothered with much of the above drugs since.
Footnotes:
1. Thus far I have been able to find DexAlone for sale only at drugstore.com and various other online retailers of OTC drugs, but I cannot for the life of me find an actual, physical store that sells it. Most places online that sell it do so in packages of 10-count 30mg tablets ($8.99 USD) and 30-count 30mg tablets ($14.99 USD). (Prices vary slightly by seller.) The price and the wait for delivery are worth it if you simply can't abide cough syrup.
Sources: (Incomplete list; I listed as many as I could find at least a little info about.)
Ambien (Sanofi-Aventis Pharmacuticals, Inc.):
http://www.ambien.com/
Ativan, Klonopin, Valium, and Xanax (generic versions by Purepac Pharmacuticals; I'm uncertain as to who holds/held the patents on the brand name drugs):
http://www.purepac.com/
Dextromethorphan (numerous manufacturers):
http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a682492.html
Diphenhydramine (numerous manufacturers):
http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a682539.html
Doxylamine (numerous manufacturers):
http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a682537.html
Halcion (Geneva Pharmacuticals, Inc.):
http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a684004.html
Lunesta (Sepracor Pharmacuticals, Inc.):
http://www.lunesta.com/
Rozerem (Takeda Pharmaceuticals North America, Inc.):
http://www.rozerem.com/
Melatonin (numerous manufacturers):
http://www.melatonin.com/
Sonata (Jones Pharma, Inc.):
http://www.sonata.com/
Valerian (numerous manufacturers):
http://www.erowid.org/herbs/valerian/