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
- not sleeping well (insomnia), or feeling very sleepy
- 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 TCAs can include:
- dry mouth
- slight blurring of vision
- problems passing urine
- 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 medicine.
Potential health risks
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's usually triggered when you take an SSRI or SNRI in combination with another medicine (or substance) that also raises serotonin levels, such as another antidepressant or St John's Wort.
Symptoms of serotonin syndrome can include:
- muscle twitching
If you experience these symptoms, you should stop taking the medicine and seek immediate advice from your GP or specialist. If this is not possible, call NHS 111.
Symptoms of severe serotonin syndrome include:
- seizures (fits)
- irregular heartbeat (arrhythmia)
If you experience symptoms of severe serotonin syndrome, seek emergency medical help immediately by dialling 999 to ask for an ambulance.
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 can happen because SSRIs can block the effects of a hormone that regulates levels of sodium and fluid in the body. Elderly people are vulnerable because fluid levels become more difficult for the body to regulate as people age.
Mild hyponatraemia can cause symptoms similar to depression or side effects of antidepressants, such as:
- feeling sick
- muscle pain
- reduced appetite
More severe hyponatraemia can cause:
- feeling listless and tired
- seizures (fits)
The most serious cases of hyponatraemia can cause you to stop breathing or enter a coma.
If you suspect 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.
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 directly causes diabetes to develop.
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".
Contact your GP, or go to hospital immediately, if you have thoughts of killing or harming yourself at any time while taking antidepressants.
It may be useful to tell a relative or close friend if you've started taking antidepressants and ask them to read the leaflet that comes with your medicines. You should then ask them to tell you if they think your symptoms are getting worse, or if they're worried about changes in your behaviour.