Several categories of prescription drugs regulate mood, each targeting different chemical systems in the brain. The main types are antidepressants, mood stabilizers, atypical antipsychotics, and a newer class of rapid-acting agents that work through the glutamate system. Which type a person takes depends on the specific condition being treated, whether that’s depression, bipolar disorder, anxiety, or a combination.
All of these drugs work by shifting the balance of chemical messengers in the brain. Three messengers play the biggest roles: serotonin, which helps regulate emotional tone and impulse control; norepinephrine, which influences alertness, energy, and stress response; and dopamine, which drives motivation and the brain’s reward system. These three systems interact constantly, and changing one inevitably affects the others.
Antidepressants
Antidepressants are the most commonly prescribed mood-regulating drugs. They come in four main classes, and all of them work by increasing serotonin, norepinephrine, or both in the spaces between brain cells.
SSRIs
Selective serotonin reuptake inhibitors are typically the first medication tried for depression and many anxiety disorders. They work by blocking the brain’s recycling of serotonin, which lets more of it stay active between nerve cells for longer. This boost in serotonin activity is what gradually lifts mood. SSRIs tend to have fewer side effects than older antidepressants, which is a major reason they became the default starting point.
SNRIs
Serotonin and norepinephrine reuptake inhibitors do essentially the same thing as SSRIs but target two chemical messengers instead of one. By also blocking the recycling of norepinephrine, they can help with both mood and energy levels. SNRIs are often tried when SSRIs haven’t worked well enough on their own, or when fatigue and low motivation are prominent symptoms.
Tricyclic Antidepressants
Tricyclics are an older class that also block the reuptake of serotonin and norepinephrine. They’re effective, but they interact with more receptor types in the brain, which means more side effects: dry mouth, constipation, sedation, and weight gain are common. Because of this, they’re generally reserved for cases where newer medications haven’t helped.
MAOIs
Monoamine oxidase inhibitors take a different approach. Instead of blocking recycling, they disable the enzyme that breaks down serotonin, norepinephrine, and dopamine. This causes all three to build up. MAOIs can be very effective, but they require strict dietary restrictions because they interact dangerously with certain foods and other medications. They’re rarely a first choice.
One drug that doesn’t fit neatly into these categories is bupropion, which primarily affects dopamine and norepinephrine rather than serotonin. It’s notable for being less likely to cause weight gain and, unlike most antidepressants, tends not to dampen sexual function.
How Long Antidepressants Take to Work
One of the most frustrating aspects of antidepressants is the delay. Although chemical changes in the brain begin almost immediately, meaningful mood improvement typically takes weeks. Some people notice subtle shifts within the first week, but only a minority achieve full remission within 10 to 14 weeks. This gap between starting a medication and feeling better is a significant challenge, particularly for people in severe depressive episodes.
It’s also worth knowing that all antidepressants carry a boxed warning from the FDA noting a possible link to suicidal thoughts and behaviors in people under 25. This warning, in place since 2007, applies to young adults through age 24. It doesn’t mean antidepressants cause suicidal behavior in most people, but it does mean younger patients are monitored more closely in the early weeks of treatment.
Mood Stabilizers
Mood stabilizers are the cornerstone of bipolar disorder treatment. While antidepressants lift mood from a low point, mood stabilizers work to keep mood from swinging too far in either direction, preventing both the highs of mania and the lows of depression.
Lithium is the oldest and best-studied mood stabilizer. It remains a first-line treatment for acute mania and long-term maintenance in bipolar I disorder. Its exact mechanism isn’t fully understood, but it appears to affect multiple signaling pathways inside brain cells. Lithium requires regular blood monitoring because the therapeutic dose is close to the toxic dose, and it can affect kidney and thyroid function over time. Weight gain is also a common concern.
Anticonvulsant medications, originally developed for epilepsy, are the other major group of mood stabilizers. Divalproex (valproate) is a first-line option for acute mania and mixed episodes, where a person experiences symptoms of mania and depression simultaneously. These drugs work by rebalancing excitatory and inhibitory signaling in the brain and influencing gene expression and cell survival. Lamotrigine is another anticonvulsant frequently used in bipolar disorder, particularly for preventing depressive episodes. It stands out for having a relatively mild side effect profile, with little risk of weight gain compared to other mood stabilizers.
Atypical Antipsychotics
Despite the name, atypical antipsychotics are now widely used for mood disorders that have nothing to do with psychosis. They regulate mood by acting on a broader set of brain receptors than antidepressants do, modulating serotonin, norepinephrine, histamine, and dopamine simultaneously. In some cases, their affinity for serotonin receptors is actually higher than their affinity for dopamine receptors, which is part of what makes them useful for mood regulation rather than just treating psychotic symptoms.
In bipolar disorder, atypical antipsychotics like quetiapine, aripiprazole, and cariprazine are considered first-line treatments for acute mania. Quetiapine is also a first-line option for bipolar depression in both bipolar I and bipolar II. For unipolar depression that hasn’t responded to antidepressants alone, adding an atypical antipsychotic is one of the most evidence-supported strategies. Clinical guidelines recommend this type of add-on therapy after two antidepressants have failed or only partially worked.
The trade-off is side effects. Some atypical antipsychotics, particularly olanzapine and clozapine, carry significant risk of weight gain, metabolic changes, and elevated cholesterol. These effects are linked to how strongly they interact with histamine and specific serotonin receptors. Others, like aripiprazole and lurasidone, have a lighter metabolic footprint. Sedation is also common with certain drugs in this class.
Rapid-Acting Treatments
The newest category of mood-regulating drugs works through an entirely different brain system: glutamate, the brain’s primary excitatory messenger. Ketamine and its derivative esketamine (available as a nasal spray) can produce noticeable antidepressant effects within hours, not weeks. This makes them fundamentally different from every other option.
At low doses, ketamine triggers a surge of glutamate release in the prefrontal cortex. Research using brain imaging has shown that glutamate cycling increases by roughly 13 to 20 percent during and shortly after administration. This burst of activity appears to strengthen connections between brain cells by stimulating growth factor signaling, essentially helping the brain rebuild weakened circuits. The antidepressant effects can last days to weeks after a single dose, though repeat treatments are typically needed.
These agents are currently reserved for treatment-resistant depression, meaning depression that hasn’t improved with at least two other medications. The treatment is administered in a clinical setting, not at home, and patients are monitored afterward because of short-term side effects like dissociation and elevated blood pressure.
When One Drug Isn’t Enough
Many people with mood disorders end up on more than one medication. When a single antidepressant provides only partial relief, the standard approach is augmentation: adding a second drug to boost the effect of the first. The best-supported augmentation strategies include adding an atypical antipsychotic, lithium, thyroid hormone, or a dopamine-enhancing compound to the existing antidepressant.
Combining two antidepressants from different classes is another approach. For example, adding bupropion (which targets dopamine and norepinephrine) to an SSRI (which targets serotonin) covers more neurochemical ground than either drug alone. Studies have also shown that pairing an atypical antipsychotic with an antidepressant can outperform either medication given individually. Finding the right combination often takes time and adjustment, but augmentation gives people with difficult-to-treat mood disorders additional options when monotherapy falls short.
Common Side Effects Across Drug Types
Every class of mood-regulating medication comes with its own side effect profile, and understanding the patterns can help you have more informed conversations about treatment. Weight gain is one of the most common concerns across categories. Among antidepressants, tricyclics, mirtazapine, and paroxetine carry the highest risk. Among antipsychotics, olanzapine and clozapine are the most likely to cause significant weight gain. Among mood stabilizers, valproate and lithium can both increase weight, while lamotrigine is largely weight-neutral. Bupropion is the only antidepressant consistently associated with modest weight loss.
Sexual side effects are particularly common with SSRIs and SNRIs. Higher serotonin levels tend to dampen the brain’s dopamine-driven reward system, which is thought to be the mechanism behind reduced sexual desire, arousal, and ability to reach orgasm. These effects are a leading reason people stop taking antidepressants. Bupropion, because it works primarily through dopamine rather than serotonin, generally avoids this problem. Sedation varies widely. It’s common with tricyclics, certain atypical antipsychotics (especially those that block histamine receptors), and some mood stabilizers like carbamazepine and valproate. SSRIs, SNRIs, and bupropion are less likely to cause daytime drowsiness.