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Selective Serotonin Reuptake Inhibitors (SSRIs)

Summary: Selective Serotonin Reuptake Inhibitors (SSRIs) are a group of medications commonly used to treat conditions such as depression and anxiety (including generalized anxiety and obsessive compulsive disorder).
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Selective Serotonin Reuptake Inhibitors (SSRIs) belong to a group of medications called antidepressants. There are six SSRIs available in Canada. These include:

  • Citalopram (Celexa®)
  • Escitalopram (Cipralex®)
  • Fluoxetine (Prozac®)
  • Fluvoxamine (Luvox®)
  • Paroxetine (Paxil®)
  • Sertraline (Zoloft®)

What are SSRIs used for?

Though these medications are called “antidepressants” they may be used for conditions other than depression. When the potential benefits (e.g., reducing your symptoms) of using an SSRI outweigh the potential risks (e.g., the side effects), many doctors prescribe one of these medications for:

  • Anxiety disorders such as generalized anxiety disorder, obsessive compulsive disorder (OCD), panic disorder, social anxiety disorder, and post traumatic stress disorder
  • Depression
  • Depression associated with bipolar disorder
  • Eating disorders
  • Selective mutism
  • Separation anxiety disorder
  • Significant premenstrual mood changes

Your doctor may be using this medication for another reason. If you are unclear why this medication is being prescribed, please ask your doctor.

How do SSRIs work?

SSRIs are known to increase the amount of a brain chemical called serotonin. It is believed that some brain chemicals, such as serotonin and norepinephrine, are not working well in people who are depressed or overly anxious. The exact way that SSRIs improve the symptoms of depression and anxiety disorders is still not fully known.

SSRIs in children and adolescents

Certain SSRIs, such as fluoxetine, sertraline and fluvoxamine have been officially approved by the FDA for use in children and adolescents in the United States.


Several SSRIs have been studied in children and adolescents diagnosed with an anxiety disorder or depression. When used to treat an anxiety disorder, there is good evidence that SSRIs are more effective than a placebo (an inactive pill that looks like medication) at decreasing symptoms of anxiety. In the treatment of OCD in particular, there is good evidence that OCD symptoms are reduced to a greater degree by an SSRI compared to a placebo. Research supports the use of certain SSRIs in children and adolescents with depression. However, some studies in childhood depression have found that certain SSRIs are not better at treating depression symptoms compared to a placebo. Whenever possible, the addition of behavioural therapy (such as Interpersonal Therapy (IPT) for depression or Cognitive Behaviour Therapy (CBT) to this medication may help to increase the potential for benefit.


In general, for depressed youth who take an SSRI for 2-3 months, about 5-6 people out of every 10 who are treated will notice an improvement in their depressive symptoms (such as depressed mood, disturbed sleep, changes in appetite, lack of energy, poor concentration and fatigue). However, in depressed youth who are given a placebo for 2-3 months, about 4-5 people out of every 10 who are treated also have a reduction in depressive symptoms.

How should an SSRI be taken?

SSRIs are usually taken once a day. SSRIs are available in several forms such as capsules, tablets and liquid (fluoxetine). You can take this medication with or without food; however there may be less stomach upset if you take it with food or milk. This medication should be taken at the same time each day as directed by your doctor. Try to connect it with something you do everyday (like eating breakfast or brushing your teeth) so that you don’t forget.


SSRIs can be taken with meals (may help decrease stomach upset), milk, water, orange or apple juice. AVOID taking SSRIs with grapefruit, because grapefruit may interact with some SSRI medications.


Usually, your doctor will start with a low dose. This dose will be slowly increased based on how you respond to it. You and your doctor can then discuss the best dosage to stay on based on how you tolerate this medication (how well the medication is working and how you are doing with the side effects of the medication) and how well it helps to decrease your symptoms.

When will the SSRI start working?

This medication needs to be taken for 3 to 6 weeks before you begin to feel better. Different symptoms may start to improve at different times. For example, improvements in sleep, appetite and energy may be seen within the first 2 weeks. Sometimes, others will notice improvements in you before you do. Full beneficial effects may take 4 to 8 weeks (or longer). Since this medication takes time to work, do not increase, decrease or stop them without discussing it with your doctor first.


If you are not feeling better within 6 to 8 weeks, your doctor may recommend you take a different medication. There is a small chance that your symptoms may worsen or that you may experience increased thoughts of self harm during the first couple of months of taking this medication (see section on side effects). If this happens, tell your doctor IMMEDIATELY.

How long do I have to take an SSRI?

This depends on the symptoms you have, how frequent they occur and how long you have had them. Most people need to take this medication for at least 6 months. This allows time for your symptoms to stabilize and for you to regain your functioning. After this time, you and your doctor should discuss the benefits and risks of continuing treatment.


If you have had several episodes of severe depressive or anxiety symptoms and you tolerate this medication well, you may be asked to take this medication for an indefinite amount of time. By continuing to take this medication, you significantly decrease the chance that you may have another episode of depression or anxiety.


Do NOT stop taking this medication (even if you are feeling better) without discussing it with your doctor first. If you stop taking this medication suddenly, it is possible that your symptoms may return or you may have a bad reaction.


Once you have started taking this medication, you and your doctor will need to monitor for both the beneficial and unwanted effects. Your doctor will check your progress and discuss changes in symptoms during the next 3 months to confirm that this medication is working properly and that possible side effects are avoided. At this time, you can discuss how long you might need to take this medication.

Are SSRIs addictive?

No, SSRIs are not addictive. You will not have “cravings” for this medication like some people do with nicotine or street drugs. If you and your doctor decide it is best for you to stop taking an SSRI, your doctor will explain how to safely lower the dose so you won’t feel any unpleasant “flu-like” effects (chills, nausea, vomiting, dizziness, tingling in hands and feet, muscle aches, fever and electrical sensations) as your body adjusts to being without this medication.

What are the side effects of an SSRI and what should I do if I get them?

As with most medications, side effects may occur when taking an SSRI. Most side effects are mild and temporary. Side effects may occur before any of the beneficial effects. It is possible for some individuals to experience side effects that they feel are serious or long lasting. If you feel this has happened, speak with your doctor right away.


Below are some of the common side effects and potentially serious side effects of taking this medication, and in brackets are suggested ways to lessen these effects.


Common side effects


Side effects may be more common when starting a medication or after a dose increase. If any of these side effects is too troublesome for you, please discuss them with your doctor, nurse or pharmacist.

  • Decreased appetite (try eating smaller, more frequent meals)
  • Diarrhea (usually disappears in the first week)
  • Difficulty sleeping (try taking the medication earlier in the day)
  • Drowsiness/fatigue (take the dose at bedtime; this usually lessens over time)
  • Energized/agitated feelings (avoid caffeine from energy drinks, colas and coffee)
  • Periods of physical restlessness
  • Headache (try using a pain reliever like acetaminophen (plain Tylenol®))
  • Stomach aches or nausea (try taking this medication with food or a glass of milk)
  • Excessive sweating (strong antiperspirants can help; talk with your doctor or pharmacist)
  • Unusually vivid dreams
  • In Adolescents/Adults: Changes in sexual performance or interest (discuss with your doctor)

Uncommon side effects (i.e., those that occur in less than 5% of patients)

  • Constipation (increase exercise, fluids, vegetables, fruits and fibre)
  • Dizziness (try getting up slowly from a sitting or lying down position)
  • Dry mouth (try chewing sugarless gum, sour candies, ice chips, or popsicles)
  • Tingling in the hands or feet (discuss with your doctor)
  • Motor tics or muscle twitches (discuss with your doctor)
  • Muscle stiffness (discuss with your doctor)
  • Lack of motivation/feelings of apathy (discuss with your doctor)
  • Decrease in the rate of growth (monitor growth)

Contact your doctor IMMEDIATELY if you have any of these uncommon, potentially serious side effects:

  • Change in mood to an unusual state of excitement, irritability or happiness
  • Seizure (also called fits or convulsions)
  • Skin rash, itchy skin or hives
  • Uncomfortable sense of inner restlessness or agitation
  • Unusual bruising or bleeding
  • Unusual sensations or experiences (e.g. hallucinations)
  • Thoughts of self harm, hostility or suicide

What precautions should my doctor and I be aware of when taking an SSRI?

Tell your doctor or pharmacist if you:

  • begin taking any other new medication (prescription or non-prescription), since several other medications can interact with SSRIs
  • feel drowsy, dizzy or slowed down. SSRIs can make some individuals experience these temporary side effects, so if you feel this way, it is important to avoid operating heavy machinery or driving a car. SSRIs may increase the effects of alcohol, resulting in more sedation or dizziness
  • have a history of diabetes, heart disease, thyroid disease, kidney or liver disease or seizures
  • have any allergies or have experienced a reaction to a medication
  • have any changes in mood or thoughts of self harm
  • if you develop any new medical problem while you are taking an SSRI
  • miss a period, become pregnant or are trying to become pregnant or are breast-feeding

What special instructions should I follow while taking an SSRI?

  • Keep all appointments with your doctor and the laboratory.
  • Do not allow anyone else to use your medication.
  • It is a good idea to have a visit or telephone call with your doctor within 1-2 weeks after you start taking an SSRI, and then periodically after that to see how well the medication is working, how well you are tolerating the medication, and to discuss any problems you may have.

What should I do if I forget to take a dose?

If you take this medication once daily at bedtime and you forget to take it, skip the missed dose and continue with your schedule the next day. Do NOT double your next dose. If you take it more than once a day, take the missed dose as soon as possible. However, if it is almost time for your next dose (e.g., within 4 hours), do not take the missed dose or double your next dose. Instead, continue your regular dosing schedule.

What storage conditions are needed for SSRIs?

  • Keep this medication in the original container, stored at room temperature away from moisture and heat (e.g., not in the bathroom or kitchen).
  • Keep this medication out of reach and sight of children.

About this Document

Special thanks to the Kelty Centre for Mental Health for permission to adapt this document. The original document was developed by health professionals of BC Mental Health and Addiction Services, and reviewed by the staff of the Kelty Mental Health Centre. French translation provided courtesy of the Ontario Centre of Excellence for Child and Youth Mental Health and the Children's Hospital of Eastern Ontario, Canada. 

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You are free to copy and distribute this material unchanged and in its entirety as long as 1) this material is not used in any way that suggests we endorse you or your use of the material, 2) this material is not used for commercial purposes (non-commercial), 3) this material is not altered in any way (no derivative works). View full license at For any other uses, please contact the original rights holder, the Kelty Mental Health Centre.


Information in this pamphlet is offered ‘as is' and is meant only to provide general information that supplements, but does not replace the information from your health provider. Always contact a qualified health professional for further information in your specific situation or circumstance.

Date Posted: Apr 27, 2013
Date of Last Revision: Nov 6, 2020

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