Rexulti (brexpiprazole) is not an SSRI. It belongs to a completely different drug class called atypical antipsychotics. While SSRIs work by blocking the reabsorption of serotonin in the brain to make more of it available, Rexulti works by fine-tuning the activity of multiple brain chemicals, including both serotonin and dopamine. The confusion likely comes from the fact that Rexulti is FDA-approved for use in major depressive disorder, but it’s prescribed alongside an antidepressant, not instead of one.
What Drug Class Rexulti Belongs To
Rexulti is classified as an atypical antipsychotic and, more specifically, a serotonin-dopamine activity modulator. Rather than simply raising serotonin levels the way an SSRI does, Rexulti acts as a partial agonist at serotonin (5-HT1A) and dopamine (D2) receptors. A partial agonist is like a dimmer switch: it stimulates the receptor enough to produce a therapeutic effect but dials back activity when natural signaling gets too high. Rexulti also blocks certain other serotonin receptors (5-HT2A) and adrenaline receptors, which contributes to its effects on mood and cognition.
SSRIs, by contrast, have a single primary action. They block the transporter protein that recycles serotonin back into nerve cells, leaving more serotonin in the gap between neurons. Common SSRIs include fluoxetine (Prozac), sertraline (Zoloft), and escitalopram (Lexapro). They are typically first-line treatments for depression, meaning doctors try them before considering add-on medications like Rexulti.
Early lab studies on animal cells did find that brexpiprazole had some ability to block serotonin and noradrenaline transporters, similar to what SNRIs do. But when researchers tested this on human cells, that transporter-blocking activity was minimal. So in practice, Rexulti does not function like an SSRI or SNRI in the human brain.
Why Rexulti Is Used for Depression
Rexulti is FDA-approved as an adjunctive treatment for major depressive disorder in adults, meaning it’s added on top of an antidepressant you’re already taking. It is not approved as a standalone depression treatment. The idea is that when an SSRI or other antidepressant isn’t providing enough relief on its own, Rexulti’s receptor-modulating effects can fill in the gaps, particularly by stabilizing dopamine signaling and enhancing serotonin activity through a different pathway than the antidepressant is using.
Clinical trials support this approach. In patients who had minimal response to their antidepressant alone, adding Rexulti produced a statistically significant improvement in depression scores after six weeks compared to adding a placebo. The effect size (Cohen’s d of 0.41) was modest but meaningful, roughly translating to a noticeable reduction in symptoms like low mood, sleep problems, and loss of interest. Patients with a partial response to their antidepressant also improved, though the benefit was smaller (Cohen’s d of 0.28).
All Three FDA-Approved Uses
Depression is only one of Rexulti’s approved indications. The full list includes:
- Adjunctive treatment for major depressive disorder in adults, added to an existing antidepressant
- Schizophrenia in adults and adolescents aged 13 and older
- Agitation associated with Alzheimer’s disease dementia, used as a scheduled daily medication rather than an as-needed treatment
The schizophrenia indication is the one most consistent with Rexulti’s classification as an antipsychotic. Its ability to partially activate dopamine D2 receptors, rather than fully blocking them, is what makes it “atypical” compared to older antipsychotics that simply shut dopamine signaling down. This partial approach aims to reduce psychotic symptoms while causing fewer movement-related side effects.
Common Side Effects
Because Rexulti acts on dopamine and serotonin receptors rather than blocking serotonin reuptake, its side effect profile looks different from what you’d expect with an SSRI. The most commonly reported side effect in clinical trials was akathisia, a feeling of inner restlessness or an inability to sit still, which affected 4 to 14 percent of patients depending on the dose and indication. Weight gain occurred in 3 to 8 percent of patients, and drowsiness in 4 to 6 percent.
SSRIs, by comparison, more commonly cause nausea, sexual dysfunction, and insomnia. Rexulti shares some warnings with other atypical antipsychotics that SSRIs don’t carry, including the potential for metabolic changes like increased blood sugar and cholesterol, a rare condition called tardive dyskinesia (involuntary repetitive movements), and drops in blood pressure when standing up.
Important Safety Warnings
Rexulti carries two boxed warnings from the FDA, the most serious type of safety alert. The first warns that antipsychotic medications increase the risk of death in elderly patients with dementia-related psychosis. This warning applies to dementia-related psychosis specifically, which is distinct from the Alzheimer’s agitation indication Rexulti was later approved for. The second warning notes an increased risk of suicidal thoughts and behaviors in patients 24 and younger, a warning shared with antidepressants in general.
How Rexulti Compares to Aripiprazole
If you’ve come across aripiprazole (Abilify), Rexulti’s closest relative, the two drugs share the same basic mechanism: partial agonism at dopamine D2 and serotonin 5-HT1A receptors. The key difference is degree. Rexulti has less intrinsic dopamine activity than aripiprazole, making it a stronger dopamine blocker in practice while still being gentler than a pure antagonist. It also has the strongest serotonin 5-HT1A stimulation of the two. This balance was designed to reduce some of the side effects associated with aripiprazole, like restlessness, nausea, and insomnia, which can result from too much dopamine receptor activation.
Both medications are approved as add-ons for depression and as treatments for schizophrenia, so they occupy a similar clinical space. Your prescriber’s choice between them often comes down to how you respond to and tolerate each one individually.