A serotonin reuptake inhibitor (SRI) is a type of drug which acts as a reuptake inhibitor of the neurotransmitter serotonin (5-hydroxytryptamine, or 5-HT) 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.
SRIs are not synonymous with selective serotonin reuptake inhibitors (SSRIs), as the latter term is usually used to describe the class of antidepressants of the same name, and because SRIs, unlike SSRIs, can either be selective or non-selective in their action. For example, cocaine, which non-selectively inhibits the reuptake of serotonin, norepinephrine, and dopamine, is an SRI but not an SSRI.
SRIs are used predominantly as antidepressants (e.g., SSRIs, SNRIs, and TCAs), though they are also commonly used in the treatment of other psychological conditions such as anxiety disorders and eating disorders. Less often, SRIs are also used to treat a variety of other medical conditions including neuropathic pain and fibromyalgia (e.g., duloxetine, milnacipran), and premature ejaculation (e.g., dapoxetine) as well as for dieting (e.g., sibutramine). Additionally, some clinically used drugs such as chlorpheniramine, dextromethorphan, and methadone possess SRI properties secondarily to their primary mechanism of action(s) and this contributes to their side effect and drug interaction profiles.
A closely related type of drug is a serotonin releasing agent (SRA), an example of which is fenfluramine.
Medication | SERT | NET | DAT |
---|---|---|---|
Citalopram | 1.16 | 4070 | 28100 |
Desmethylcitalopram | 3.6 | 1820 | 18300 |
Escitalopram | 1.1 | 7841 | 27410 |
Femoxetine | 11.0 | 760 | 2050 |
Fluoxetine | 0.81 | 240 | 3600 |
Fluvoxamine | 2.2 | 1300 | 9200 |
Norfluoxetine | 1.47 | 1426 | 420 |
Paroxetine | 0.13 | 40 | 490 |
Sertraline | 0.29 | 420 | 25 |
Desmethylsertraline | 3.0 | 390 | 129 |
Zimelidine | 152 | 9400 | 11700 |
Levomilnacipran [3] | 19.0 | 10.5 | ND |
Venlafaxine | 8.9 | 1060 | 9300 |
Vilazodone [3] | 1.6 | ND | ND |
Vortioxetine [3] | 5.4 | ND | ND |
Amitriptyline | 4.30 | 35 | 3250 |
Clomipramine | 0.28 | 38 | 2190 |
Imipramine | 1.40 | 37 | 8500 |
Medication | Dosage range (mg/day) [4] | ~80% SERT occupancy (mg/day) [5] [6] | Ratio (dosage / 80% occupancy) |
---|---|---|---|
Citalopram | 20–40 | 40 | 0.5–1 |
Escitalopram | 10–20 | 10 | 1–2 |
Fluoxetine | 20–80 | 20 | 1–4 |
Fluvoxamine | 50–350 | 70 | 0.71–5 |
Paroxetine | 10–60 | 20 | 0.5–3 |
Sertraline | 25–200 | 50 | 0.5–4 |
Duloxetine | 20–120 | 30 | 0.67–2 |
Venlafaxine | 75–375 | 75 | 1–5 |
Clomipramine | 50–250 | 10 | 5–25 |
Many SRIs exist, an assortment of which are listed below. Note that only SRIs selective for the SERT over the other monoamine transporters (MATs) are listed below. For a list of SRIs that act at multiple MATs, see other monoamine reuptake inhibitor pages such as SNRI and SNDRI.
Antidepressants are a class of medications used to treat major depressive disorder, anxiety disorders, chronic pain, and addiction.
Monoamine transporters (MATs) are proteins that function as integral plasma-membrane transporters to regulate concentrations of extracellular monoamine neurotransmitters. The three major classes are serotonin transporters (SERTs), dopamine transporters (DATs), and norepinephrine transporters (NETs) and are responsible for the reuptake of their associated amine neurotransmitters. MATs are located just outside the synaptic cleft (peri-synaptically), transporting monoamine transmitter overflow from the synaptic cleft back to the cytoplasm of the pre-synaptic neuron. MAT regulation generally occurs through protein phosphorylation and post-translational modification. Due to their significance in neuronal signaling, MATs are commonly associated with drugs used to treat mental disorders as well as recreational drugs. Compounds targeting MATs range from medications such as the wide variety of tricyclic antidepressants, selective serotonin reuptake inhibitors such as fluoxetine (Prozac) to stimulant medications such as methylphenidate (Ritalin) and amphetamine in its many forms and derivatives methamphetamine (Desoxyn) and lisdexamfetamine (Vyvanse). Furthermore, drugs such as MDMA and natural alkaloids such as cocaine exert their effects in part by their interaction with MATs, by blocking the transporters from mopping up dopamine, serotonin, and other neurotransmitters from the synapse.
Serotonin–norepinephrine reuptake inhibitors (SNRIs) are a class of antidepressant medications used to treat major depressive disorder (MDD), anxiety disorders, social phobia, chronic neuropathic pain, fibromyalgia syndrome (FMS), and menopausal symptoms. Off-label uses include treatments for attention-deficit hyperactivity disorder (ADHD), obsessive–compulsive disorder (OCD), and migraine prevention. SNRIs are monoamine reuptake inhibitors; specifically, they inhibit the reuptake of serotonin and norepinephrine. These neurotransmitters are thought to play an important role in mood regulation. SNRIs can be contrasted with the selective serotonin reuptake inhibitors (SSRIs) and norepinephrine reuptake inhibitors (NRIs), which act upon single neurotransmitters.
Clomipramine, sold under the brand name Anafranil among others, is a tricyclic antidepressant (TCA). It is used in the treatment of various conditions, most-notably obsessive–compulsive disorder but also many other disorders, including panic disorder, major depressive disorder, trichotilomania, body dysmorphic disorder and chronic pain. It has also been notably used to treat premature ejaculation and the cataplexy associated with narcolepsy.
Mesembrine is an alkaloid present in Sceletium tortuosum (kanna). It has been shown to act as a serotonin reuptake inhibitor (Ki = 1.4 nM), and more recently, has also been found to behave as a weak inhibitor of the enzyme phosphodiesterase 4 (PDE4) (Ki = 7,800 nM). In an in vitro study published in 2015, researchers concluded that "a high-mesembrine Sceletium extract" may exert anti-depressant effects by acting as a monoamine releasing agent." As such, mesembrine likely plays a dominant role in the antidepressant effects of kanna. The levorotatory isomer, (−)-mesembrine, is the natural form.
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 spontaneous orgasm, or spontaneous ejaculation when it occurs in males, is an orgasm which occurs spontaneously and involuntarily without sexual stimulation. Nocturnal emissions may be considered a normal/physiological form of spontaneous orgasm. Pathological spontaneous orgasms can be experienced as pleasurable, non-pleasurable, or unpleasant, and can be distressing. Causes of pathological spontaneous orgasms include spinal cord lesions, psychological causes, rabies, and medications. Some cases may have no identifiable cause. Spontaneous orgasms may have no trigger or may be triggered by various non-sexual circumstances. They may occur in both males and females. Treatment of spontaneous orgasms include psychotherapy, selective serotonin reuptake inhibitors (SSRIs), the alpha-1 blocker silodosin, and anxiolytics.
The number of new psychiatric drugs, and especially antidepressants on the market in Japan, is significantly less than Western countries.
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.
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.
Vortioxetine, sold under the brand names Trintellix and Brintellix among others, is a medication used to treat major depressive disorder. Its effectiveness is viewed as similar to that of other antidepressants. It is taken by mouth.
Selective serotonin reuptake inhibitors (SSRIs) are a class of drugs that are typically used as antidepressants in the treatment of major depressive disorder, anxiety disorders, and other psychological conditions.
Dapoxetine, marketed as Priligy, among others, is a selective serotonin reuptake inhibitor (SSRI) used for the treatment of premature ejaculation (PE) in men 18–64 years old. Dapoxetine works by inhibiting the serotonin transporter, increasing serotonin's action at the postsynaptic cleft, and as a consequence promoting ejaculatory delay. As a member of the selective serotonin reuptake inhibitor (SSRI) family, dapoxetine was initially created as an antidepressant. However, unlike other SSRIs, dapoxetine is absorbed and eliminated rapidly in the body. Its fast-acting property makes it suitable for the treatment of PE, but not as an antidepressant.
A monoamine reuptake inhibitor (MRI) is a drug that acts as a reuptake inhibitor of one or more of the three major monoamine neurotransmitters serotonin, norepinephrine, and dopamine by blocking the action of one or more of the respective monoamine transporters (MATs), which include the serotonin transporter (SERT), norepinephrine transporter (NET), and dopamine transporter (DAT). This in turn results in an increase in the synaptic concentrations of one or more of these neurotransmitters and therefore an increase in monoaminergic neurotransmission.
Mesembrenone is an alkaloid constituent of Sceletium tortuosum (Kanna) and minor constituent of Lampranthus aureus and Lampranthus spectabilis
A serotonin modulator and stimulator (SMS), sometimes referred to more simply as a serotonin modulator, is a type of drug with a multimodal action specific to the serotonin neurotransmitter system. To be precise, SMSs simultaneously modulate one or more serotonin receptors and inhibit the reuptake of serotonin. The term was created to describe the mechanism of action of the serotonergic antidepressant vortioxetine, which acts as a serotonin reuptake inhibitor (SRI), agonist of the 5-HT1A receptor, and antagonist of the 5-HT3 and 5-HT7 receptors. However, it can also technically be applied to vilazodone, which is an antidepressant as well and acts as an SRI and 5-HT1A receptor partial agonist.
Selective serotonin reuptake inhibitors, or serotonin-specific re-uptake inhibitor (SSRIs), are a class of chemical compounds that have application as antidepressants and in the treatment of depression and other psychiatric disorders. SSRIs are therapeutically useful in the treatment of panic disorder (PD), posttraumatic stress disorder (PTSD), social anxiety disorder, obsessive-compulsive disorder (OCD), premenstrual dysphoric disorder (PMDD), and anorexia. There is also clinical evidence of the value of SSRIs in the treatment of the symptoms of schizophrenia and their ability to prevent cardiovascular diseases.
PPPA, or 3-phenoxy-3-phenylpropan-1-amine, is a drug which is described as an antidepressant. It was derived by Eli Lilly from the antihistamine diphenhydramine, a diphenylmethane derivative with additional properties as a selective serotonin reuptake inhibitor (SSRI), and has been the basis for the subsequent discovery of a number of other antidepressant drugs.