Modern sleeping pills of the benzodiazepine type are to some extent better than the older barbiturates, in that suicidal and accidental overdose are uncommon. Increasingly, however, people are becoming aware that all the benzodiazepines are not alike. Some persist in the tissues much longer than others, and some involve larger doses than others before they produce the effect that is desired. Yet another complication is that many of the drugs form breakdown products within the body that are very slowly eliminated. The drug flurazepam is characterized by its persistence in the system, to the extent that it accumulates in the tissues until it reaches a plateau in seven to 14 days. No wonder its takers so often feel strange in the daytime when on this sleeping pill.
Some of the benzodiazepines, especially flurazepam, diazepam and nitrazepam, have long ‘half-lives’ (the time between taking the drug and half of it being eliminated from the body). When this happens large amounts persist in the tissues next day and uncharacteristic behaviour on the part of the taker – for instance shoplifting or aggression – may occur, and minor crime may be committed.
There are of course extremely short-acting benzodiazepines, for example triazolam with its half-life of only three hours. When this was introduced doctors felt that here at last was the ideal sleeping pill. Alas, due to the rebound phenomenon (see page 235) such a quickly-eliminated drug is ineffective in sustaining sleep and the taker often wakes up early in the morning awash with rebound anxiety.
One well-known sleep research authority suggests the best compromise is a drug with a half-life of about ten hours. Lormetazepam is such a drug. This, if taken at 11 p.m. allows for a small amount to be present on waking – hopefully just enough to avoid a sharp daytime rebound of anxiety.
All the drugs I have so far mentioned are only available on a doctor’s prescription. There are also available several over-the-counter sleeping pills, but few are very effective. An exception is promethazine (Phenergan) which is available in several strengths and as an elixir. It belongs to the class of drugs designated as antihistamine, and is an anti-allergic remedy with a sedative action. Like many antihistamines it does have a considerable sedative and prolonged action in most people, although in a few it has, paradoxically, the opposite effect.