What are sedatives ?
A sedative or tranquilliser is a substance that induces sedation by reducing irritability or excitement. They are central nervous depressants and interact with brain activity causing its deceleration.
Various kinds of sedatives can be distinguished, but the majority of them affect the neurotransmitter gamma-aminobutyric acid (GABA). Thus, these are brain chemicals performing communication between brain cells. In spite of the fact that each sedative acts in its own way, they produce beneficial relaxing effect by increasing GABA activity.
At higher doses it may result in slurred speech, staggering gait, poor judgment, and slow, uncertain reflexes. Doses of sedatives such as benzodiazepines, when used as a hypnotic to induce sleep, tend to be higher than amounts used to relieve anxiety, whereas only low doses are needed to provide a peaceful effect.
Sedatives can be misused to produce an overly-calming effect (alcohol being the classic and most common sedating drug). In the event of an overdose or if combined with another sedative, many of these drugs can cause unconsciousness and even death.
Mechanism of action and effects
Sedatives are usually classified according to the way they affect the human body. They represent a diverse group of drugs that share an ability to reduce activity of CNS and diminish the brain’s level of awareness. The lack of similarity between the structures of drugs that belong to different classes made it difficult to propose a common receptor or mechanism of action.
This is best explained if we observe two commonly prescribed groups of drugs - barbiturates and benzodiazepines. For example, barbiturate-type drugs cause general depression of most neuronal activity, thus they are considered nonselective. That is the reason why their use is practically always accompanied by certain degree of cognitive function impairment.
In contrast, benzodiazepines selectively affect the neurons that have receptors for the neurotransmitter gamma-aminobutyric acid (GABA).This is a crucial inhibitory transmitter in several regions of the brain. In the presence of these drugs, the inhibitory effects of GABA are increased, which explains the selective CNS depression caused by benzodiazepines.
Absorption of most sedatives is fairly rapid and it goes through gastrointestinal tract. Two mentioned groups of drugs are primarily absorbed in the small intestine, and clinical effects are determined by their ability to penetrate the blood-brain barrier. Most sedatives are metabolized to pharmacologically active intermediates, and elimination occurs predominantly by hepatic metabolism.
The effects of the sedatives tend to be dose dependent, and often the only difference between anxiolytic and hypnotic effect is the dose. Consequently, the same drug can be used for both purposes just by varying the dose. By increasing the dose even further, an anesthetic state can be reached.