What side effects can antidepressants cause?

Every antidepressant has possible side effects. These vary between the different the different types  of antidepressant, and between each individual drug. This page covers: 

  • Which side effects may be caused by each type of antidepressant? 
  • How might these side effects affect me? 

Some of the side effects listed below are quite common, while others are rare. You may not  experience many of these effects. You may also experience some side effects when you first start  taking antidepressants, but feel them less after a few weeks. 

It’s up to you to decide whether or not the antidepressant has more benefits for you than any  negative side effects. Your doctor should be able to help you with this decision. 

What side effects may be caused by each type of  antidepressant? 

These are the side effects that each type of antidepressant may cause. They list the most common at  the top and least common at the bottom for each type of antidepressant, with links to more  information below: 

SSRIs and SNRIs 

  • decreased alertness 
  • headaches 
  • nausea (feeling sick) 
  • sexual problems 
  • tooth decay and oral health 
  • diabetes 
  • SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion) 
  • gastrointestinal bleeding 
  • serotonin syndrome 
  • suicidal feelings 
  • neuroleptic malignant syndrome
  • hypomania or mania 

Tricyclic and tricyclic-related antidepressants 

  • antimuscarinic effects 
  • tooth decay and oral health 
  • decreased alertness 
  • suicidal feelings 
  • serotonin syndrome 
  • SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion) 
  • diabetes 
  • neuroleptic malignant syndrome 
  • hypomania or mania 


  • decreased alertness 
  • SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion) 
  • serotonin syndrome 
  • diabetes 
  • suicidal feelings
  • neuroleptic malignant syndrome

How might these side effects affect me? 

This section gives information explaining how each of the side effects listed above might affect you  and your body. 

Antimuscarinic effects 

Antimuscarinic effects are side effects caused by changes to the level of the chemical acetylcholine  in your body. These effects are sometimes called anticholinergic effects. 

If your level of acetylcholine changes, this can have effects all over the body. These effects include: 

  • blurred vision 
  • confusion and agitation
  • constipation, which may become life-threatening if not treated 
  • difficulty urinating 
  • drowsiness 
  • dry mouth, which can cause tooth decay in the long term 
  • erectile dysfunction 
  • hallucinations 
  • hot or dry skin, and decreased sweating 
  • increased pressure in the eye 
  • low blood pressure (taking hot baths increases this risk) 
  • nausea (feeling sick)
  • rapid heartbeat and disturbed heart rhythm.

Decreased alertness 

Antidepressants can make you feel less alert or able to concentrate. This can happen especially  when you first start taking them. This may affect your ability to drive and to do other skilled tasks. 


Long-term use of antidepressants over several years may increase the risk of diabetes. This is  especially in people who are: 

  • over the age of 30 
  • taking SSRIs or tricyclics. 

Gastrointestinal bleeding 

A rare side effect of some SSRI antidepressants is bleeding inside your gastrointestinal system, which  includes your stomach and intestines. 

The risk of gastrointestinal bleeding is higher for older people, especially those aged over 80. If you  are over 80, your doctor may prescribe you a different antidepressant to avoid this risk. 

Hypomania or mania 

Antidepressants may trigger hypomania or mania in some people. This may stop if you stop taking  the antidepressant. But sometimes it may be a sign of bipolar disorder. In this case, you may be  given a new diagnosis and different medication.

Neuroleptic malignant syndrome 

NMS is a rare but serious neurologic disorder, which means it affects your nervous system. It usually  happens as a side effect of antipsychotic drugs. But it can sometimes happen with antidepressants. If  it does occur, it usually develops rapidly over 24 to 72 hours. 

The symptoms of NMS may include : 

  • sweating or fever, with a high temperature 
  • tremor (shaking), rigidity (feeling stiff and unable to move your muscles) or loss of  movement 
  • difficulty speaking and swallowing 
  • rapid heartbeat, very rapid breathing and changes in blood pressure 
  • changes in consciousness, including confusion, lethargy or going into a coma. 

High temperature and rigidity are usually the first symptoms to appear. This means NMS can  sometimes be confused with an infection. But NMS can be very dangerous if it’s not detected and  treated. In rare cases, it can be fatal. 

If you’re worried that you may have symptoms of NMS, speak to your doctor urgently or call 999  for an ambulance.

What’s the treatment for NMS? 

If you experience NMS, you may  need treatment in hospital, where doctors can stop your medication and reduce your fever. 

Some other methods of treatment are used, although the evidence for the use of these is not as  strong. These methods may include: 

  • using medication to relax your muscles 
  • using medication to counter the chemical effects that are thought to cause NMS 
  • electroconvulsive therapy (ECT). 

The symptoms may last for days, or even weeks, after coming off the medication that’s causing them. Many people who have had NMS once are at a higher risk of getting it again. 

If you experience NMS, you should only take antidepressants afterwards only if they are essential for your mental health. And you should have the lowest dosage possible that still gives the positive effects.

Serotonin syndrome

This is a rare but serious condition, which can be fatal. It can happen with any antidepressant, but is  more likely with an SSRI. This is especially if you take an SSRI alongside certain other drugs, such as  another antidepressant or lithium. 

This list includes some of the more common symptoms of serotonin syndrome. If you experience these symptoms, you should seek immediate advice from your doctor or a specialist involved in your care: 

  • headaches 
  • nausea (feeling sick) 
  • diarrhoea 
  • high temperature, shivering and sweating 
  • tremors, muscle twitching and over-responsive reflexes 
  • agitation, confusion and hallucinations 
  • rapid heartbeat and high blood pressure. 

These are some rare symptoms of NMS, but if you experience them it is a medical emergency. If  you have these symptoms, you or someone else should call 999 and ask for an ambulance to take  you to hospital

  • convulsions (fits) 
  • irregular heartbeat (arrhythmia)
  • coma (loss of consciousness).

Sexual problems 

Certain sexual problems are a potential negative side effect of all SSRI and SNRI antidepressants.  These include: 

In women: 

  • delayed orgasm or inability to reach orgasm 
  • spontaneous orgasm 

In men: 

  • reduced sexual desire 
  • failed erection, delayed ejaculation and lack of orgasm 
  • priapism (prolonged erection) – this requires urgent medical attention, so if you experience  this side effect, you should go to A&E or get a same-day appointment with your doctor.

Sometimes these side effects persist after you’ve come off the drug, and might continue indefinitely. You should speak to your medical professional for more information and clarity.

SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion) 

SIADH is a side effect of some antidepressants. It mainly happens with tricyclics, SSRIs and SNRIs. It is  a rare but serious side effect, which can be fatal. 

Vasopressin is one of the hormones that control the production of urine in your body. It is also  known as the antidiuretic hormone. 

SIADH makes your body secrete too much vasopressin. This causes your body to hold on to water,  which lowers the level of sodium in your body. This condition is called hyponatraemia. It can lead to: 

  • confusion 
  • convulsions (fits) 
  • hallucinations 
  • coma (loss of consciousness)
  • memory problems, difficulty concentrating, drowsiness and falls (mainly seen in older people).

Suicidal feelings 

There is a possibility that taking an antidepressant could make you feel suicidal. It may happen even  if you didn’t experience suicidal feelings before. 

This side effect is mainly with SSRI antidepressants. But it is a risk with all antidepressants. 

If you feel unable to keep yourself safe, it’s a mental health emergency. 

Get emergency advice


Some people believe antidepressants might make you more likely to act on suicidal feelings. This is  because antidepressants can increase your energy and motivation levels, which may be very low  while you are depressed. Early in your treatment, you may experience more energy and motivation  before your feelings of depression have started to lift. This might mean you have enough energy to act on suicidal urges. 

This is only a theory. Lots of people who take antidepressants don’t experience suicidal feelings. And  if you do experience these feelings, it doesn’t always mean that you will act on them. 

But it is still important to get help. You can speak to your doctor about how you are feeling. Or see  our page on treatment and support for suicidal feelings for other ways to get help. 

Tooth decay and oral health

Any drugs which cause a dry mouth can also cause tooth decay if you take them for a long time. This  side effect is most common with tricyclic antidepressants. 

You can speak to your dentist if you are concerned about this. They can give advice on how to care  for your teeth and oral health while you are taking antidepressants. 

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