This is a list of investigational antidepressants, or drugs that are currently under development for clinical use in the treatment of depression but are not yet approved. Specific indications include major depressive disorder, treatment-resistant depression, dysthymia, bipolar depression, and postpartum depression, among others.
Chemical/generic names are listed first, with developmental code names, synonyms, and brand names in parentheses.
This list was last comprehensively updated in August 2024. It is likely to become outdated with time.
Noradrenergic and specific serotonergic antidepressants (NaSSAs) are a class of psychiatric drugs used primarily as antidepressants. They act by antagonizing the α2-adrenergic receptor and certain serotonin receptors such as 5-HT2A and 5-HT2C, but also 5-HT3, 5-HT6, and/or 5-HT7 in some cases. By blocking α2-adrenergic autoreceptors and heteroreceptors, NaSSAs enhance adrenergic and serotonergic neurotransmission in the brain involved in mood regulation, notably 5-HT1A-mediated transmission. In addition, due to their blockade of certain serotonin receptors, serotonergic neurotransmission is not facilitated in unwanted areas, which prevents the incidence of many side effects often associated with selective serotonin reuptake inhibitor (SSRI) antidepressants; hence, in part, the "specific serotonergic" label of NaSSAs.
A serotonin–norepinephrine–dopamine reuptake inhibitor (SNDRI), also known as a triple reuptake inhibitor (TRI), is a type of drug that acts as a combined reuptake inhibitor of the monoamine neurotransmitters serotonin, norepinephrine, and dopamine. It does this by concomitantly inhibiting the serotonin transporter (SERT), norepinephrine transporter (NET), and dopamine transporter (DAT), respectively. Inhibition of the reuptake of these neurotransmitters increases their extracellular concentrations and, therefore, results in an increase in serotonergic, adrenergic, and dopaminergic neurotransmission. The naturally-occurring and potent SNDRI cocaine is widely used recreationally and often illegally for the euphoric effects it produces.
A serotonin reuptake inhibitor (SRI) is a type of drug which acts as a reuptake inhibitor of the neurotransmitter serotonin by blocking the action of the serotonin transporter (SERT). This in turn leads to increased extracellular concentrations of serotonin and, therefore, an increase in serotonergic neurotransmission. It is a type of monoamine reuptake inhibitor (MRI); other types of MRIs include dopamine reuptake inhibitors and norepinephrine reuptake inhibitors.
The serotonin 1A receptor is a subtype of serotonin receptors, or 5-HT receptors, that binds serotonin, also known as 5-HT, a neurotransmitter. 5-HT1A is expressed in the brain, spleen, and neonatal kidney. It is a G protein-coupled receptor (GPCR), coupled to the Gi protein, and its activation in the brain mediates hyperpolarization and reduction of firing rate of the postsynaptic neuron. In humans, the serotonin 1A receptor is encoded by the HTR1A gene.
Reuptake inhibitors (RIs) are a type of reuptake modulators. It is a drug that inhibits the plasmalemmal transporter-mediated reuptake of a neurotransmitter from the synapse into the pre-synaptic neuron. This leads to an increase in extracellular concentrations of the neurotransmitter and an increase in neurotransmission. Various drugs exert their psychological and physiological effects through reuptake inhibition, including many antidepressants and psychostimulants.
Vilazodone, sold under the brand name Viibryd among others, is a medication used to treat major depressive disorder. It is classified as a serotonin modulator and is taken by mouth.
Serotonin antagonist and reuptake inhibitors (SARIs) are a class of drugs used mainly as antidepressants, but also as anxiolytics and hypnotics. They act by antagonizing serotonin receptors such as 5-HT2A and inhibiting the reuptake of serotonin, norepinephrine, and/or dopamine. Additionally, most also antagonize α1-adrenergic receptors. The majority of the currently marketed SARIs belong to the phenylpiperazine class of compounds.
S32212 is a drug which is under preclinical investigation as a potential antidepressant medicine. It behaves as a selective, combined 5-HT2C receptor inverse agonist and α2-adrenergic receptor antagonist (at all three subtypes—α2A, α2B, and α2C) with additional 5-HT2A and, to a lesser extent, 5-HT2B receptor antagonistic properties, and lacks any apparent affinity for the monoamine reuptake transporters or for the α1-adrenergic, H1, or mACh receptors. This profile of activity is compatible with the definition of a noradrenergic and specific serotonergic antidepressant (NaSSA), and as such, S32212 could in turn be classified as a NaSSA.
A trip killer, or hallucinogen antidote, is a drug that aborts or reduces the effects of a hallucinogenic drug experience. As there are different types of hallucinogens that work in different ways, there are different types of trip killers. They can completely block or reduce the effects of hallucinogens or they can simply provide anxiety relief and sedation. Examples of trip killers, in the case of serotonergic psychedelics, include serotonin receptor antagonists, like antipsychotics and certain antidepressants, and benzodiazepines. Trip killers are sometimes used by recreational psychedelic users as a form of harm reduction to manage so-called bad trips, for instance difficult experiences with prominent anxiety. They can also be used clinically to manage effects of hallucinogens, like anxiety and psychomotor agitation, for instance in the emergency department.
Solriamfetol hydrochloride, previously known as JZP-110, SKLN05, ARL-N05, YKP-10A, R-228060, ADX-N05, was initially developed by the SK Group as YKP-10A, a drug to treat depression. SK Group licensed rights outside of 11 countries in Asia to Aerial BioPharma in 2011. [...]
Regardless, a more parsimonious explanation is that certain 5-HT2 receptor-activating compounds, such as DOI and psilocin, cause specific conformations of 5-HT2 receptors that lead to LSD-like psychedelic effects.[94,232] Moreover, although the 5-HT2 agonists mCPP, lorcaserin, and quipazine, are often considered 'non-hallucinogenic', they actually do produce perceptual, cognitive, and emotional changes that may be considered 'hallucinogenic'.[15,233,234] These effects, however, are generally not considered LSD-like. Finally, it is noteworthy that novel, partial 5-HT2A/D2 receptor agonists also attenuate the DOI-elicited HTR.[235,236]
This concept is also supported by experiments on OSU-6162, a selective Sigma 1R ligand in low doses [176]. This Sigma1R ligand produced in the nucleus accumbens shell substantial increases in the density of the D2R–Sigma1R and A2AR–D2R heterocomplexes, supporting the existence of A2AR–D2R–Sigma1R trimeric complexes in which the Sigma1R agonist can strongly enhance the antagonistic allosteric A2AR–D2R interaction. This mechanism may mediate the enhanced antagonistic A2AR–D2R interaction, causing marked inhibition of cocaine reward, leading to cocaine addiction.
ALTO-300 is a 25 mg formulation of the atypical antidepressant agomelatine, which targets the melatonin and serotonin signaling systems and has been shown to modulate mood and circadian rhythms. This medication is approved for the treatment of depression in several countries outside of the United States.
BRII-296 is an extended-release injectable aqueous suspension formulation of brexanolone. Phase 1 trials in 116 subjects testing 6 dose regimens are complete with the sponsor reporting that a single intramuscular injection of 600 mg achieved dose linearity, early drug absorption, and gradual and extended-release profiles without the need for dose titration or tapering, however results have not been published (Brii Biosciences Limited 2023b).
DGX-001, Viage's clinical drug candidate, represents a first-in-class oral drug candidate targeting the gut-brain axis. The proposed mechanism of action of DGX-001 is to modulate the vagus nerve through specific receptor interactions on enteroendocrine cells in the gut, resulting in a regulation of brain cell activity.
[SK2110 - Buprenorphine implant for the treatment of major depressive disorder SK2110 is an implant of buprenorphine hydrochloride for patients with major depression and refractory depression who cannot be relieved by taking at least two drugs. Buprenorphine hydrochloride was developed by Indivior and is a KOR1 antagonist and MOR1 agonist. Currently, the highest development stage of the drug is approval for marketing, which is used to treat opioid dependence, chronic pain, pain and substance-related disorders. The company changes the route of administration to prepare an implant, which can reduce the frequency of administration, improve the bioavailability of the drug, improve patient compliance, and maintain a stable blood drug concentration, thereby reducing adverse drug reactions. At the same time, the implanted administration method can also play a role in avoiding drug abuse. At present, the project is conducting laboratory preparation small-scale trial prescription process exploration and preliminary pharmacodynamic studies. SK2110 can take effect quickly and quickly relieve patients' depressive symptoms. It is expected to submit an IND application to my country's drug regulatory authorities in 2024.]
Centpropazine, possessing the 1-aryloxy-3-(piperazin-1-yl)propan-2-ol scaffold is an antidepressant, only marketed in India, and has never been clinically approved likely due to its low bioavailability (Figure 2).10 To the best of our knowledge, the exact modes of action of centpropazine are unclear. The fact that centpropazine possesses antidepressant effects is remarkable. Although its efficacy in treating depressive symptoms has been previously investigated,11-13 its pharmacological studies of the specific monoamines affected have not been reported.
Because AMPA appeared critical to ketamine's antidepressant effects, researchers reasoned that AMPA positive modulators—also known as AMPAkines—could positively influence mood. Previous studies evaluating AMPAkines in mood disorders achieved mixed results, potentially due to low bioavailability and toxicity profile.20 To overcome the issue of low bioavailability, other AMPAkines were recently developed and tested in initial Phase 1 and 2 studies, particularly coluracetam (BCI-540)21 and ORG-26576.22 Both agents showed preliminary therapeutic effects in major depressive disorder when tested in small samples.23,24
The 5-HT1B/1D receptor antagonist elzasonan (CP-448187) was recently under development for the treatment of MDD and was tested in several phase-2 clinical trials, but its development program was also discontinued.140
In general, piracetam-like nootropics show no affinity for the most important central receptors (Ki > 10 μM). A modest affinity for muscarinic receptors is shown by aniracetam (Ki = 4.4 μM [58]) and nebracetam (Ki = 6.3 μM [61]). Nefiracetam is the only one showing affinity in the nanomolar range (Ki = 8.5 nM on the GABAA receptor [58]). [...] Nefiracetam (chart (1)) is awaiting approval. It presents a variety of pharmacological actions as it is reported to activate the cholinergic, GABAergic and other monaminergic systems and to modulate N-type calcium channels [78-81].
As mentioned above, no commonly accepted mechanism for the racetam nootropics has yet been established, They do not seem to act on any well characterised receptor site with the exception of nefiracetam which has high affinity for GABA, receptors (see Table 1). [...] Receptor: GABAA. Receptor ligand: [3H]muscimolA. Compound: nefiracetam. IC50: 8.5 nMB. Refs.: 222. [...] From Table 1 it is, however, evident that the piracetam-like nootropics do not exhibit high affinity for any of the receptor types tested so far (except for nefiracetam, which shows some activity at GABAA receptors)
The close structural analog of DETQ, LY3154207, is currently in phase 2 testing for Lewy Body dementias, including patients with Parkinson's disease.