What Are SSRIs and How Do Antidepressants Work

This page reflects our understanding of mental health topics as of 2026. If you are reading this at a later date, some details may no longer be current, so please verify anything important against up to date sources. If you notice anything that needs updating, we would welcome you letting us know.

SSRIs, or selective serotonin reuptake inhibitors, are the most commonly prescribed antidepressants. They are used to treat depression, anxiety disorders, OCD, PTSD, and some other conditions. SSRIs increase the availability of serotonin, a brain chemical involved in mood and anxiety, by slowing how quickly it is reabsorbed by nerve cells. Their benefits usually build gradually over two to six weeks or longer, while some side effects can appear earlier and often ease with time. Common SSRIs include sertraline, escitalopram, citalopram, fluoxetine, paroxetine, and fluvoxamine. SSRIs are prescribed by physicians, nurse practitioners, and psychiatrists, and they are often most effective when combined with therapy.

How Antidepressants Work

Serotonin is one of several chemical messengers in the brain. The older idea that depression is simply a "chemical imbalance" is now considered too simple. Current research suggests antidepressants may work through several processes, including changes in how brain networks process emotional information and adapt over time. This helps explain why their full effect develops gradually rather than right away.

Types of Antidepressants

• SSRIs. Often a first choice because of their effectiveness and tolerability.
• SNRIs. Serotonin and norepinephrine reuptake inhibitors, such as venlafaxine and duloxetine.
• Other antidepressants. Medications such as bupropion and mirtazapine work in different ways.
• Older antidepressants. Tricyclics and MAOIs are used less often because of side effects and interactions.

What to Expect When Starting

Timing

Some people notice improvements in sleep or energy within the first couple of weeks, while mood and anxiety often take longer. A fair trial usually means several weeks at an effective dose.

Common Side Effects

Nausea, headaches, changes in sleep, feeling jittery, and sexual side effects can occur. Many early side effects ease within a few weeks. Sexual side effects may persist and are worth discussing with your prescriber.

Safety Monitoring

Regulators have warned that some children, teens, and young adults may experience increased suicidal thoughts when starting an antidepressant or changing the dose, so close monitoring early in treatment is important at any age.

Stopping

Stopping suddenly can cause discontinuation symptoms, such as dizziness, irritability, and flu-like feelings. Always talk to your prescriber about tapering gradually.

Questions to Ask Your Prescriber

Before starting an antidepressant, it can help to ask how long it may take to work, which side effects are common, what to do if you miss a dose, how long you might take it, and how you will decide together whether it is helping. Keeping a simple mood log during the first weeks can make follow-up appointments more productive.

How Medication Fits With Therapy

For mild depression, therapy alone is often recommended first. For moderate to severe depression, medication, therapy, or both can be effective, and the combination often works best, as described on the page about medication vs. therapy for depression. For anxiety disorders, both CBT and SSRIs are effective, as described on the page about medication for anxiety. Therapy can also help prevent relapse after medication is stopped.

What It Is Not

Antidepressants are not addictive in the way some drugs are, and they do not change your personality. They are also not a sign of weakness. If the first medication does not help, another often will. If depression has not responded to several treatments, the page about treatment-resistant depression describes further options.

Who Prescribes Antidepressants in BC

Family doctors, nurse practitioners, and psychiatrists prescribe antidepressants. Psychologists and counsellors do not prescribe medication but often work closely with prescribers. The page about how depression is treated explains the full range of options.

Getting Support at Pacific Maple Psych Centre

If you are considering medication or already taking it, therapy can work alongside it to help you feel better and stay well.