The side effects of antidepressants can cause problems at first but then generally improve with time.

It is important to persist with treatment, even if you are affected by side effects, as it will take several weeks before you begin to benefit from treatment. With time you should find the benefits of treatment outweigh any problems from side effects.

During the first few months of treatment, you will usually see your doctor or a specialist nurse at least once every 2-4 weeks to see how well the medication is working.

Some of the more common side effects of the main types of antidepressants are outlined below. For more information about side effects of your specific medication, see the patient information leaflet that comes with it or look up your medicine in the Medicines A-Z.

SSRIs and SNRIs

Common side effects of selective serotonin reuptake inhibitors (SSRIs) and serotonin-noradrenaline reuptake inhibitors (SNRIs) can include:

• feeling agitated, shaky or anxious
• feeling and being sick
• indigestion and stomach aches
• diarrhoea or constipation
• loss of appetite
• dizziness
• not sleeping well (insomnia), or feeling very sleepy
• headaches
• low sex drive
• difficulties achieving orgasm during sex or masturbation
• in men, difficulties obtaining or maintaining an erection (erectile dysfunction)

These side effects should improve within a few weeks, although some can occasionally persist.

Tricyclic antidepressants (TCAs)

Common side effects of tricyclic antidepressants (TCAs) can include:

• dry mouth
• slight blurring of vision
• constipation
• problems passing urine
• drowsiness
• dizziness
• weight gain
• excessive sweating (especially at night)
• heart rhythm problems, such as noticeable palpitations or a fast heartbeat (tachycardia)

The side effects should ease after a couple of weeks as your body begins to get used to the medication.

MAOIs

Common side effects of monoamine oxidase inhibitors (MAOIs) can include:

• constipation
• drowsiness
• dry mouth
• dizziness (particularly after sudden movements, such as standing up quickly)
• feeling sick
• tiredness and difficulty sleeping

In rare cases, MAOIs have the potential to cause a wide range of other side effects. You should check with your GP or mental health specialist if you are concerned about any unusual symptoms that you have.

There have been cases where MAOIs have caused a dangerous rise in blood pressure. This can cause symptoms such as:

• a stiff neck
• severe headache
• chest pains
• feeling or being sick
• an abnormally fast heartbeat

If you experience the combination of symptoms listed above, seek emergency medical help immediately by dialling 999 to ask for an ambulance.

Potential health risks

Serotonin syndrome

Serotonin syndrome is an uncommon, but potentially serious, set of side effects linked to SSRIs and SNRIs.

Serotonin syndrome occurs when the levels of a chemical called serotonin in your brain become too high. It is usually triggered when you take an SSRI or SNRI in combination with another medication (or substance) that also raises serotonin levels, such as another antidepressant or St John’s Wort.

Symptoms of serotonin syndrome can include:

• confusion
• agitation
• muscle twitching
• sweating
• shivering
• diarrhoea

If you experience the symptoms listed above, you should stop taking the medication and seek immediate advice from your GP or specialist. If this is not possible, call NHS 111.

Symptoms of severe serotonin syndrome include:

• a very high temperature (fever)
• seizures (fits)
• irregular heartbeat (arrhythmia)
• unconsciousness

If you experience symptoms of severe serotonin syndrome, seek emergency medical help immediately by dialling 999 to ask for an ambulance.

Hyponatraemia

Elderly people who take antidepressants, particularly those who take SSRIs, may experience a severe fall in sodium (salt) levels known as hyponatraemia. This may lead to a build-up of fluid inside the cells of the body, which can be potentially dangerous.

This side effect can occur as SSRIs can block the effects of a hormone that helps regulate levels of sodium and fluid in the body. Elderly people are vulnerable because fluid levels become more difficult for the body to regulate.

Mild hyponatraemia can cause symptoms similar to depression or side effects of antidepressants, such as:

• feeling sick
• headache
• muscle pain
• reduced appetite
• confusion

More severe hyponatraemia can cause the following symptoms:

• feeling listless and tired
• disorientation
• agitation
• psychosis (being unable to tell the difference between reality and your imagination)
• seizures (fits)

The most serious cases of hyponatraemia can cause you to stop breathing or enter a coma.

If you suspect that you, or someone in your care, has mild hyponatraemia you should call your GP for advice and stop taking SSRIs for the time-being.

If you suspect severe hyponatraemia, call 999 and ask for an ambulance.

Hyponatraemia can be treated by feeding a sodium solution into the body through an intravenous drip.

Diabetes

Long-term use of SSRIs and TCAs has been linked to an increased risk of developing type 2 diabetes, although it's not clear if the use of these antidepressants causes diabetes to develop directly.

It may be that the weight gain some people using antidepressants experience increases the risk of them developing type 2 diabetes.

For more information, see 'Claim that antidepressants cause diabetes unproven'.

Suicidal thoughts

Some people experience suicidal thoughts and a desire to self-harm when they first take antidepressants. Young people under 25 seem particularly at risk.

Contact your GP, or go to hospital immediately, if you have thoughts of killing or harming yourself at any time while you are taking antidepressants.

It may be useful to tell a relative or close friend you have started taking antidepressants and ask them to read the leaflet that comes with your medication. You should then ask them to tell you if they think your symptoms are getting worse, or if they are worried about changes in your behaviour.