n. a drug designed to alleviate the symptoms of *depression. Most antidepressants act by altering the availability of *serotonin and *noradrenaline in the brain; they are also likely to influence synaptic transmission regulation and postsynaptic conduction. There are four main classes of antidepressants. The selective serotonin reuptake inhibitors, such as fluoxetine, sertraline, escitalopram, and citalopram (see SSRI), are recommended as first-line treatment for depression and anxiety by current NICE guidelines. Their mode of action is entirely on serotonin. Side-effects include gastrointestinal problems and nausea. Tricyclic antidepressants, such as *imipramine, *doxepin, *lofepramine, *clomipramine, and *amitriptyline, are also widely used. They act on noradrenaline as well as serotonin, although most of them primarily have a noradrenergic action. They are also used in chronic pain management. Their side-effect profile varies from that of SSRIs; on the whole they have more *antimuscarinic effects and are more sedative. They are more dangerous in overdose than SSRIs and cause more weight gain. Other side-effects include postural hypotension. Serotonin and noradrenaline reuptake inhibitors), such as venlafaxine and duloxetine (see SNRI), are a common second-line choice in the treatment of depression and anxiety. Monoamine oxidase inhibitors (MAOIs), such as the reversible moclobemide and the irreversible phenelzine (see MAO inhibitor), are older antidepressants. They are now less used because of significant side-effects and interactions with other drugs. The irreversible MAOIs also require certain dietary restrictions. Antidepressants are not addictive, but depending on their half-life they show a varying prevalence of *discontinuation syndrome. Antidepressants have consistently been shown to be more effective than placebo. Their efficacy is lower in mild depression but moderate to good in moderate and severe depression. They are part of the gold-standard treatment for depression and anxiety.... antidepressant