The choice of antidepressant should be discussed with patients to ensure they understand the likely side effects, interactions with concomitant medicines, effect on other health problems and discontinuation symptoms. This also affords an opportunity to explore any previous experience they have had with the drug class, particularly in terms of efficacy and tolerability, and assess the risk of suicide so the danger of toxicity in overdose can be taken into account.

It can take two weeks for the antidepressant effect to be felt, during which time there may be an increased risk of anxiety, agitation and suicidal ideation, so the need for adherence should be emphasised. Severe cases may require hospitalisation and/or electroconvulsive therapy during this time, while others may require a short-term benzodiazepine. Those at increased risk of suicide should be monitored closely. 

1. Selective serotonin reuptake inhibitors (SSRIs) 
   Six SSRIs are licensed for depression in the UK (fluoxetine, paroxetine, citalopram, escitalopram, sertraline and fluvoxamine). Some important considerations are:
   An increased risk of bleeding, particularly in older people and those taking other drugs that interfere with clotting or have the potential to damage the gastrointestinal mucosa (e.g. NSAIDs and aspirin)
   Fluoxetine, fluvoxamine and paroxetine are associated with more drug interactions than other SSRIs while paroxetine also has a higher incidence of discontinuation symptoms due its shorter half-life.

2. Serotonin and noradrenaline reuptake inhibitors (SNRIs) 
   These are regarded as newer-generation antidepressants. Venlafaxine and duloxetine are the only SNRIs licensed in the UK for the management of depression but the following needs to be kept in mind:
   Venlafaxine is associated with a greater risk of death from overdose, and at high doses can exacerbate cardiac arrhythmias 
   Both venlafaxine and duloxetine can exacerbate hypertension.

3. Tricyclic antidepressants (TCAs) 
   These are an option for those for whom the side effect of sedation is desirable (amitriptyline and clomipramine are among those in the drug class more associated with drowsiness; those less inclined to sedate include lofepramine and imipramine). TCAs are also an option for the elderly as the risk of hyponatraemia (a low level of sodium in the blood) is lower than is the case with SSRIs. The higher incidence of side effects, which include postural hypotension and arrythmias, and risk of toxicity in overdose, need to be taken into consideration.

4. Monoamine oxidase inhibitors (MAOIs) 
   These include phenelzine and moclobemide and are normally only prescribed by mental health specialists due to the high number of interactions with other medicines and foods.