An antidepressant is a type of psychiatric drug usually used for treating major depressive disorder (unipolar depression). It is worth noting that many of these agents are not effective for bipolar disorder-associated depression and that antipsychotics such as lurasidone (Latuda) and quetiapine (Seroquel) are used for this purpose.
Types of antidepressants
Serotonin reuptake inhibitors
Dextromethorphan Because dextromethorphan can show similar antidepressant effects to ketamine in threshold and light dosages, it is possible that dextromethorphan could be a possible treatment for treatment resistant and severe depression. Many users claim that a single use of dextromethorphan alleviates their depression for up to a week. This may be a related to its activity as a reuptake inhibitor of serotonin. However, it is believed to have neurotoxic properties so its routine use as an antidepressant is not advised.
Selective serotonin reuptake inhibitors (SSRIs)
Selective serotonin reuptake inhibitors are believed to increase the level of extracellular serotonin, therefore allowing more serotonin to be in the brain. The reason SSRIs are used for depression is that the serotonin hypothesis, one of the most commonly accepted theories for depression, states that low serotonin in the brain causes depression. SSRIs are the most commonly prescribed antidepressant, and the most commonly prescribed anxiolytic for children. They are also the first-line treatment for panic disorder, not benzodiazepines like lorazepam and alprazolam.
Serotonin-norepinephrine reuptake inhibitor (SNRIs)
Serotonin-norepinephrine reuptake inhibitors increase the level of extracellular serotonin and norepinephrine, allowing more of the neurotransmitters to be in the brain. SNRIs are used for depression because the serotonin hypothesis states that low serotonin in the brain causes depression, and also to treat tiredness commonly experienced with depression.
Serotonin modulators and stimulators (SMSes)
Serotonin antagonists and reuptake inhibitors (SARIs)
Serotonin releasing agents (SRAs)
The psychoactive effects caused by these agents can be mainly attributed to their mechanism of action by inducing release of serotonin into the neuronal synaptic cleft. Causing an increased concentration and availability of serotonin in the brain. Even though drugs such as MDMA can be technically referred to as SRA’s, it’s however more accurate classification would be an SNDRA over an SRA. Since unlike Selective serotonin releasing agents (SSRA’s) such as PMA (common cutting agent used for MDMA) which only effects serotonin release, MDMA also induces the release of both dopamine and norepinephrine. It should be noted that PMA and other SSRA’s/SRA’s alike are typically not considered to be reinforcing(addictive) as they lack appreciable dopaminergic and adrenergic activity. On the other hand substances such as Methamphetamine and MDMA are addictive In nature due to their euphoric action on dopamine which is further amplified through their secondary role as SRA’s. FYI Methamphetamine is a very weak SRA so you most likely see it called an NDRA (Norepinephrine/dopamine releasing agent) over an SNDRA.
Norepinephrine reuptake inhibitors (NRIs)
- NRIs are believed to increase the level of extracellular norepinephrine, therefore allowing more of it to be in the brain. Controversy has been sparked over the effectiveness of reboxetine, an NRI sold as Edronax.  Norepinephrine reuptake inhibitors can treat the tiredness commonly experienced with depression.
Norepinephrine-dopamine reuptake inhibitors (NDRIs)
- NDRIs are believed to increase the level of extracellular norepinephrine and dopamine, therefore allowing more of these to be in the brain. Agents such as bupropion (Wellbutrin) have been found effective for MDD with little direct effect on serotonin, and therefore it can be hypothesized that other agents are effective for it. Bupropion and other NDRIs are also effective for depression with fatigue or sleepiness.
Tricyclic antidepressants (TCAs)
Tetracyclic antidepressants (TeCAs)
Monoamine Oxidase Inhibitors (MAOIs)
MAOIs are usually prescribed when no other antidepressants are helping. This is because MAOIs require diet changes and have a very large amount of side effects. MAOIs mainly prevent the breakdown of monoamine neurotransmitters in the brain such as serotonin, dopamine, and norepinephrine.
Psilocybin and other classical psychedelics such as LSD have been researched as a treatment for depression and anxiety disorders. Studies have shown that psilocybin is highly effective in reducing overall depression and anxiety.
In clinical studies, ketamine has proven to be an extremely effective and fast acting antidepressant at low doses (compared to common recreational doses). It has become increasingly common for doctors to prescribe ketamine for treatment-resistant depression, severe depression, and addiction.
- "Comparative efficacy and acceptability of 12 new-generation antidepressants: a multiple-treatments meta-analysis." Multiple authors (2009) https://www.researchgate.net/profile/Andrea_Cipriani/publication/23967068_Comparative_efficacy_and_acceptability_of_12_new-generation_antidepressants_A_multiple-treatments_meta-analysis/links/00b7d5278b5bed4c17000000.pdf