Health psychology (option): SSRIs and SNRIs for anxiety

How SSRIs work

Recall synaptic transmission (Unit 2): neurotransmitter is released into the synapse, binds to receptors, then is taken back into the presynaptic neuron (reuptake).

SSRIs block the reuptake of serotonin only (selective), so more serotonin stays in the synapse for longer and keeps stimulating the postsynaptic receptors. Serotonin is linked to mood and emotion; low serotonin activity is associated with anxiety and depression.

• Examples: sertraline, citalopram, escitalopram, fluoxetine, paroxetine.
• Used for depression and anxiety disorders, including generalised anxiety disorder, panic disorder, social anxiety, OCD and PTSD.
• Usually the first type prescribed because side effects are generally easier to manage.
• They take 1 to 2 weeks to start working and up to 8 weeks to work fully; people usually continue for at least 6 months after feeling better.

How SNRIs work

SNRIs block the reuptake of both serotonin and noradrenaline (norepinephrine), increasing the levels of both in the synapse. Noradrenaline is also linked to mood, alertness and arousal.

• Examples: venlafaxine, duloxetine.
• Used as an alternative to SSRIs for anxiety and depression.

Side effects and evaluation

Common side effects (NHS): feeling agitated or shaky, sleep problems, headaches, dizziness, nausea, dry mouth, sweating, sexual problems. Suicidal thoughts are uncommon but can occur when starting, especially in people aged 24 or under, so close monitoring is needed. People must not stop suddenly because of withdrawal effects.

Evaluation:

• Strengths: easy to take, widely available, no need for weekly sessions; supported by controlled trials; can reduce symptoms enough for people to engage with therapy.
• Weaknesses: side effects lead some people to stop; delay before working; they treat symptoms, not the causes of anxiety, so relapse is common after stopping; the serotonin explanation is reductionist and the drugs do not help everyone; long-term use raises dependence and withdrawal concerns. Ethical issue: informed consent when side effects are uncertain.

Worked example

Explain how an SSRI could reduce anxiety.

1. Normally serotonin is reabsorbed into the presynaptic neuron after it is released (reuptake).
2. An SSRI blocks this reuptake, so serotonin stays in the synapse longer.
3. More serotonin keeps stimulating postsynaptic receptors, which is thought to improve mood and reduce anxiety.

Answer: Blocking serotonin reuptake increases serotonin activity at the synapse.

Check yourself

1. What do SSRIs do at the synapse?
   • Block the reuptake of serotonin
   • Block the reuptake of serotonin and noradrenaline
   • Destroy serotonin receptors
   • Release cortisol
   Show answer

   Block the reuptake of serotonin. Selective serotonin reuptake inhibition.

2. SNRIs increase the levels of which neurotransmitters?
   • Dopamine only
   • Serotonin only
   • Serotonin and noradrenaline
   • GABA and glutamate
   Show answer

   Serotonin and noradrenaline. Serotonin and norepinephrine reuptake inhibitors.

3. Which is an example of an SNRI?
   • Venlafaxine
   • Sertraline
   • Fluoxetine
   • Citalopram
   Show answer

   Venlafaxine. Venlafaxine and duloxetine are SNRIs.

4. According to the NHS, up to how many weeks can SSRIs take to work fully?
   Show answer

   8. 1 to 2 weeks to start; up to 8 weeks fully.

5. Which is a weakness of SSRIs and SNRIs?
   • They work immediately
   • They treat symptoms rather than the causes of anxiety
   • They need weekly therapy sessions
   • They have no side effects
   Show answer

   They treat symptoms rather than the causes of anxiety. Relapse often follows stopping.

6. Explain how SSRIs work.
   Show answer

   SSRIs block the reuptake of serotonin into the presynaptic neuron, so more serotonin remains in the synapse and continues to stimulate the postsynaptic receptors.. Block, reuptake, serotonin.

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Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Psychology specification, Issue 6 (November 2024, first assessment January 2026)
• NHS: SSRI antidepressants
• NHS: Antidepressants overview (SSRIs and SNRIs)

Last updated 8 November 2026. Spotted a mistake? Tell us.