What Side Effects Can Antidepressants Trigger?

Different antidepressants can cause a range of side effects, from very common to extremely rare. You might have some, none, or they may fade after a few weeks as your body adjusts.

Before starting or stopping an antidepressant, always talk to your doctor.

Common Side Effects Across All Antidepressants

Most antidepressants can cause a few everyday side effects, especially in the first few weeks such as:

• Nausea or stomach upset
• Diarrhoea or constipation
• Tiredness or feeling drowsy
• Trouble sleeping (or feeling more awake than usual)
• Headaches
• Dizziness or feeling faint
• Dry mouth
• Weight changes (gain or loss)
• Increased sweating
• Feeling more anxious at first

Side Effects by Antidepressant Type

Some side effects are linked to specific types of antidepressant:

SSRIs and SNRIs

• Sexual problems (loss of desire, delayed orgasm)
• Serotonin syndrome (rare, serious reaction)
• SIADH (low sodium levels, rare but dangerous)
• Bleeding in the stomach or gut (more likely if over 80 or on blood thinners)
• Suicidal thoughts or feelings (especially in under‑25s)
• Hypomania or mania (can reveal bipolar disorder)

Tricyclics

• Antimuscarinic effects (blurred vision, dry mouth, constipation, rapid heartbeat)
• Sexual problems
• Heart rhythm changes (arrhythmias — dangerous in overdose)
• Suicidal thoughts or feelings
• SIADH (rare)
• Hypomania or mania

MAOIs

• Reduced alertness
• “Cheese reaction” – dangerous rise in blood pressure if certain foods are eaten (tyramine sensitivity)
• Serotonin syndrome (rare, serious reaction)
• SIADH (rare)
• Suicidal thoughts or feelings

How Long Do Side Effects Last?

Many common side effects like nausea, tiredness, or headaches fade after the first few weeks as your body adjusts. Some, like sexual side effects or weight changes, may continue for longer, talk to your doctor if they don’t improve.

When to Seek Help

Contact your GP or pharmacist if:

• Side effects are bothersome or don’t go away
• You notice new issues like diabetes symptoms or weight changes
• You’re unsure if what you’re feeling is normal for your medication

Call emergency services if:

• You have signs of serotonin syndrome — sudden confusion, high fever, severe muscle stiffness
• You experience seizures or pass out
• You have a severe allergic reaction — swelling of face or throat, or trouble breathing