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Selective Serotonin Reuptake Inhibitors (SSRI)

9. Glossary of terms


Abnormal fear or anxiety induced by being in crowds or in open spaces—environments which seem difficult to escape from or obtain help


Sensation of restlessness and a compulsion to move constantly.

Anticholinergic effects

See Antimuscarinic effects—most anticholinergic effects involve the muscarinic receptor for acetylcholine.

Antidepressants, MAOI

Monoamine oxidase inhibitors act within nerve cells to block the enzyme that promotes breakdown of the monoamine neurotransmitters, noradrenaline and serotonin. Therefore, nerve endings can release more neurotransmitter at the synapse. Examples of MAOI antidepressants include isocarboxazid, phenelzine, and tranylcypromine. The antidepressant, moclobemide, is a reversible inhibitor of monoamine oxidase type A (RIMA).

Antidepressants, SNRI

Serotonin and noradrenaline reuptake inhibitors reduce the uptake of both serotonin and noradrenaline, leaving more of the neurotransmitters at the synapse to act on the other nerve cell. Duloxetine and venlafaxine are SNRI antidepressants.

Antidepressants, tricyclic

Tricyclic antidepressants (with a 3-ring molecular structure) inhibit the reuptake of noradrenaline by nerve endings, leaving more noradrenaline at the synapse to act on the other nerve cell. Some tricyclic antidepressants also inhibit the reuptake of serotonin. Examples of tricyclic (and related) antidepressants are: amitriptyline, clomipramine, dosulepin, imipramine, and trazodone.

Antimuscarinic effects

Reduction or blocking of the effects of parasympathetic nerves; antimuscarinic effects include dry mouth, difficulty swallowing, blurred vision, confusion, palpitations, constipation, and urine retention.

Antiplatelet medicines

Antiplatelet medicines are used to prevent heart attacks and strokes. They prevent platelets from clumping together, which, in turn, helps to prevent the formation of clots. Antiplatelet medicines include aspirin, clopidogrel, dipyridamole, and prasugrel.


Joint pain.


Class of medicines which have a sedating effect, most often used for anxiety and insomnia, but also used for muscle relaxation, managing convulsions, and as premedication for surgery and certain procedures. The class includes: chlordiazepoxide, diazepam, flurazepam, lorazepam, midazolam, nitrazepam, oxazepam, and tempazepam.

Bipolar disorder

A psychiatric disorder characterised by two or more episodes in which mood and activity levels are significantly disturbed by elevation of mood (hypomania or mania) or lowering of mood (depression); historically also known as ‘manic–depressive disorder’.


Compulsive or chronic need for a chemical substance (eg alcohol, benzodiazepine, or opioid).


A psychiatric disorder characterised by lowered mood, reduced energy and decreased activity. The severity of a depressive episode is divided clinically into mild, moderate and severe subtypes (the latter may or may not have psychotic features). Repeated episodes of depression, without a history of mania, are classified as recurrent depressive disorder.

Dopamine receptor agonist

A chemical substance that binds to dopamine receptors on cells, thereby triggering a response by that cell. Dopamine receptors are found on many neurones of the central nervous system, particularly those involved in motor control, pleasure and reward, memory and cognition and neuroendocrine modulation. There are at least five major subtypes of dopamine receptor: D1 to D5. In medicine, dopamine receptor agonists are given to compensate for deficit of endogenous dopamine, in conditions such as Parkinson’s disease.


Reduction of response to a substance (such as a hormone or neurotransmitter) that normally produces a particular effect. Often this results from a loss of functioning receptors in response to an excess of the substance that interacts with the receptor.


A movement disorder characterised by sustained muscle contractions, resulting in abnormal posturing or repetitive writhing movements.


An enantiomer is one of a pair of chemical molecules with identical molecular formula, but one enantiomer cannot be superimposed on the other because it is a mirror image of the other. Often one enantiomer exerts considerably more biological activity than the other.

Histamine H2 antagonist

Histamine H2 antagonists reduce the secretion of acid in the stomach. They are used to prevent and heal duodenal and gastric ulcers and to manage other conditions aggravated by stomach acid. Examples of this class of medicine include cimetidine and ranitidine.


See Serotonin.


A disorder in which reflexes are exaggerated and overactive.


A disorder characterised by persistent and inappropriate mild elevation of mood, increased energy and activity. There are usually marked feelings of well-being and of both physical and mental efficiency. The disturbances of mood and behaviour are not accompanied by hallucinations or delusions.


A persistent mood elevation out of keeping with the individual’s circumstances, characterised by symptoms such as excitement, irritability, loss of need for sleep, grandiosity and loss of inhibition. The symptoms are extreme and the individual may not be able to control them. Delusions or hallucinations may be present.


Medicines and Healthcare products Regulatory Agency, a government body which regulates many aspects of the testing, manufacture, supply, and use of medicines and medical devices.

Monoamine oxidise B inhibitors

Monoamine oxidase (MAO) is an enzyme involved in the breakdown of monoamine neurotransmitters, such as serotonin, dopamine and noradrenaline. MAO-B inhibitors (eg rasagiline and selegiline) are used in the treatment of Parkinson’s disease whereas MAO-A inhibitors are used as antidepressants (see Antidepressants, MAOI).


Muscle pain.


Brief, involuntary twitching of the muscles which may produce a spasmodic or jerking movement.


A chemical substance released by a nerve cell at the junction between two nerve cells (synapse), which can stimulate or inhibit the other nerve cell. Examples of neurotransmitters include acetylcholine, dopamine, noradrenaline and serotonin.


Involuntary and jerky eye movement and inability to look steadily at an object.


Sensation of numbness or tingling in the skin, popularly known as ‘pins and needles’.

Proton pump inhibitor

Proton pump inhibitors reduce the secretion of acid in the stomach; they are used to prevent and heal duodenal and gastric ulcers and to manage other conditions aggravated by stomach acid. Examples of this class of medicine include esomeprazole, lansoprazole, and omeprazole.

Psychotropic drugs

A chemical substance which can alter brain function, resulting in changes in consciousness, cognition, perception, mood or behaviour.

Seizure threshold

The point at which the excitatory (seizure-inducing) impulses upon the brain outweigh the inhibitory (seizure-reducing) impulses, leading to a seizure. A substance which reduces the seizure threshold increases the probability that a stimulus will produce a seizure, especially in those with neurological predisposition to seizures, such as sufferers of epilepsy.


A chemical agent (or synapse) that produces its effects via the serotonin transmitter system.


Serotonin (also called 5-hydroxytryptamine) is a neurotransmitter in the brain. It also has activity on platelets, gastrointestinal system and on blood vessels.

Serotonin syndrome

A potentially life-threatening medical emergency, characterised by excessive serotonin stimulation. This is usually the result of an overdose of a single serotonergic substance or the mixture and additive effect of several serotonergic substances. A variety of symptoms are produced, which range from the relatively unnoticeable to extreme and fatal.


A junction between two nerve cells. A signal is transmitted from one cell to the other by the release of a chemical neurotransmitter which diffuses across the gap between the cells and interacts with specific receptors on the other cell.

Teratogenic effects

An abnormality of embryonic development caused by an external agent. An example would be a birth defect caused by the effects of a drug. The first three months of fetal development (first trimester) are particularly sensitive to teratogenic effects of medicines.


Drugs that bind to serotonin (5HT1) receptors in cranial blood vessels. They are used in the treatment of migraine headaches. Examples include sumatriptan and zolmitriptan.