Selective serotonin reuptake inhibitors

SSRI stands for Selective Serotonin Reuptake Inhibitor. SSRI antidepressants are a type of antidepressant that have been shown to increase levels of serotonin within the brain.

Serotonin is a neurotransmitter that is often referred to as the “feel good hormone”. It carries messages between brain cells and contributes to well-being, good mood, appetite, as well as helping to regulate the body’s sleep-wake cycle and internal clock. Historically, it was thought that depression was caused by low levels of serotonin and other neurotransmitters in the brain, although experts now do not think this is the case.

SSRIs increase levels of serotonin in the brain by preventing the reuptake of serotonin by nerves. All SSRI antidepressants have this effect.

Antidepressants relieve the symptoms of depression. SSRIs are one type of antidepressant. Other types include tricyclic antidepressants (TCAs), serotonin and norepinephrine reuptake inhibitors (SNRIs), norepinephrine and dopamine reuptake inhibitors (NDRIs), monoamine oxidase inhibitors (MAOIs), and the atypical antidepressants.

What are SSRI antidepressants used for?

SSRI antidepressants help to relieve symptoms of depression such as low mood, irritability, feelings of worthlessness, restlessness, anxiety, and difficulty in sleeping.

They are one of the most commonly prescribed antidepressants because they are effective at improving mood with fewer or less severe side effects compared to some other antidepressants.

In addition to depression, SSRIs may also be used to treat a range of other conditions, for example:

• Anxiety
• Bulimia nervosa
• Fibromyalgia
• Hot flashes
• Obsessive-compulsive disorder
• Panic disorder
• Post-Traumatic Stress Disorder
• Premenstrual dysphoric disorder

Some reduction in symptoms may be noticed within one to two weeks; however, it may take six to eight weeks of treatment before the full effects are seen.

What are the differences between SSRI antidepressants?

Although all SSRI antidepressants are thought to act in the same way, there are differences between individual SSRIs with regards to how long they remain in the body, how they are metabolized, and how much they interact with other medications. For example, fluoxetine, fluvoxamine, and paroxetine are more likely to interact with other medications than citalopram, escitalopram and sertraline.

*Vilazodone is considered a serotonin modulator. Exactly how it works for depression is unknown but it does appear to potentiate serotonergic activity in the CNS. 

Are SSRI antidepressants safe?

When taken at the recommended dosage, SSRI antidepressants are considered safe. However, they have been associated with a few serious, potentially fatal, severe side effects such as:

• An increase in suicidal thoughts and behaviors, particularly in children and young adults under the age of 25 years. This is most likely to occur when starting therapy
• Serotonin syndrome – this is caused by excessive levels of serotonin in the body and is more likely to occur with higher dosages of SSRIs or when SSRIs are administered with other medications that also release serotonin (such as dextromethorphan, tramadol, and St. John's Wort). Symptoms include agitation, confusion, sweating, tremors, and a rapid heart rate
• An increase in the risk of bleeding, especially if used with other medications that also increase bleeding risk.

In addition, some SSRIs, such as citalopram have been associated with abnormal heart rhythms with higher dosages.

What are the side effects of SSRI antidepressants?

Not everybody experiences side effects with SSRIs antidepressants. Some of the more commonly reported side effects include:

• Blurred vision
• Dizziness
• Drowsiness (fluoxetine is more likely to cause insomnia)
• Dry mouth
• Gastrointestinal upset (such as constipation, diarrhea, or nausea)
• Headache
• Sexual dysfunction (such as reduced desire or erectile dysfunction).

Several SSRIs have been associated with a discontinuation syndrome when they have been stopped suddenly. For this reason, it is best to withdraw all antidepressants slowly.

For a complete list of side effects, please refer to the individual drug monographs.