Every antidepressant has the potential to cause particular side effects, and these can vary from drug to drug (for details of the possible side effects of a particular antidepressant, look it up in our antidepressants A–Z). 

Remember that while some side effects are quite common, many of them are rare, and not everyone experiences them.

It's up to you to decide whether or not the antidepressant has more
benefits for you than side effects. (See our page on coping with side effects for more information).

It took me a long time to take an SSRI, mainly as I was terrified of the side effects listed, but my doctor finally convinced me that my depression was much worse [than the side effects].

There are some side effects that are common to all antidepressants of a particular type.

For guidance on what to do if you experience a side effect, see our page on coping with side effects.

Antimuscarinic effects

Antimuscarinic effects (sometimes called anticholinergic effects) is the medical term for a group of side effects which can occur with many different types of drugs – especially tricyclic antidepressants.

They 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
• hallucinations
• hot or dry skin, and decreased sweating
• increased pressure in the eye
• low blood pressure (taking hot baths increases this risk)
• rapid heartbeat and disturbed heart rhythm
• trembling

These side effects can happen because, as well as affecting brain chemicals related to mood, the drug can also affect brain chemicals which control the different functions in your body.

Decreased alertness

Antidepressants can make you feel less alert or able to concentrate. This can affect:

• driving
• other skilled tasks

Diabetes

Long-term use of antidepressants over several years is associated with an increased risk of diabetes, especially in people who are:

• over the age of 30
• taking SSRIs or tricyclics

Hypomania or mania

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

Neuroleptic malignant syndrome

This is a rare, but serious, condition. It is usually associated with antipsychotic drugs (sometimes known as neuroleptics), but can occasionally occur with antidepressants.

The symptoms include:

• changes in your level of consciousness
• fast heart rate
• high temperature
• pale skin
• stiffness
• sweating
• unstable blood pressure
• urinary incontinence

Serotonin syndrome

This is a serious condition which, although rare, can be fatal. It can occur with any antidepressant, but is more likely with an SSRI – especially if you take it alongside other antidepressants, including MAOIs, and lithium (a mood stabiliser).

The symptoms are (most common first):

• headaches
• nausea (feeling sick)
• diarrhoea
• high temperature, shivering and sweating
• high blood pressure and a fast heart rate
• tremors, muscle twitching and over-responsive reflexes
• convulsions (fits)
• agitation, confusion and hallucinations
• coma (loss of consciousness)

These symptoms may come on very suddenly.

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 GP

Sometimes these side effects persist after you've come off the drug, and might continue indefinitely. If you experience this, you might want to report it on a Yellow Card.

SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion)

SIADH is a rare side effect of some antidepressants – mainly tricyclics, SSRIs and SNRIs.

The antidiuretic hormone (vasopressin) is one of the hormones that control the production of urine. SIADH makes your body secrete too much antidiuretic hormone, which causes your body to hold on to water and makes you become low in sodium (this condition is called hyponatraemia).

This can lead to:

• confusion
• convulsions (fits)
• hallucinations
• coma (loss of consciousness), potentially leading to death
• memory problems, difficulty concentrating, drowsiness and falls (mainly in older people)

Suicidal feelings

There is a possibility that taking an antidepressant could make you feel suicidal – even if you didn’t experience suicidal feelings before. This side effect is mainly associated with SSRI antidepressants, although all antidepressants carry this risk.

How could an antidepressant cause suicidal feelings?

There are two possible explanations:

• When you’re severely depressed, your energy and motivation levels are very low, but taking an antidepressant can change this. A common theory for explaining suicide in the early stages of treatment is that the drug might give you the energy to act on suicidal urges before your depression has really started to lift.
• A number of scientists believe that some drugs might directly cause suicidal thoughts and urges. The discussion usually focuses on SSRIs in particular, but research suggests that all antidepressants carry similar risks.

Tooth decay

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 commonly associated with tricyclic antidepressants. 

This information was published in 2016. We will revise it in 2018.