Venlafaxine is an arylalkanolamine serotonin-norepinephrine reuptake inhibitor, which is sold under several brand names; one of them is venlafaxine hydrochloride. Venlafaxine hydrochloride is a venlafaxine extended release tablets, which are indicated for the treatment of major depressive disorder (MDD). Efficacy of venlafaxine in MDD was shown in both short-term trials and a longer-term trial in MDD. A major depressive episode (DSM-IV) implies a prominent and relatively persistent depressed mood or the loss of interest or pleasure in nearly all activities, representing a change from previous functioning, and includes the presence of at least five of the following nine symptoms during the same two-week period. In addition, venlafaxine hydrochloride is indicated for the treatment of social anxiety (SAD), also known as social phobia. Social Anxiety Disorder (DSM-IV) is characterized by a marked and persistent fear of 1 or more social or performance situations in which others expose to unfamiliar people or to possible scrutiny the person. Exposure to the feared situation almost invariably provokes anxiety, which may approach the intensity of a panic attack. The feared situations are avoided or endured with intense anxiety or distress. The mechanism of the antidepressant action of venlafaxine in humans is believed to be associated with its potentiation of neurotransmitter activity in the CNS. Preclinical studies have shown that venlafaxine and its active metabolite, O-desmethylvenlafaxine (ODV), are potent inhibitors of neuronal serotonin and norepinephrine reuptake and weak inhibitors of dopamine reuptake.

Paroxetine, also known by the trade names Paxil and Seroxat. PAXIL (paroxetine hydrochloride) is an orally administered psychotropic drug. It is the hydrochloride salt of a phenylpiperidine compound identified chemically as (-)-trans-4R-(4'fluorophenyl)-3S-[(3',4'-methylenedioxyphenoxy) methyl] piperidine hydrochloride hemihydrate. It is used to treat major depressive disorder, obsessive-compulsive disorder, social anxiety disorder, panic disorder, posttraumatic stress disorder, generalized anxiety disorder and premenstrual dysphoric disorder. Paroxetine is a potent and highly selective inhibitor of neuronal serotonin reuptake. Paroxetine likely inhibits the reuptake of serotonin at the neuronal membrane, enhances serotonergic neurotransmission by reducing turnover of the neurotransmitter, therefore it prolongs its activity at synaptic receptor sites and potentiates 5-HT in the CNS; paroxetine is more potent than both sertraline and fluoxetine in its ability to inhibit 5-HT reuptake. Compared to the tricyclic antidepressants, SSRIs have dramatically decreased binding to histamine, acetylcholine, and norepinephrine receptors. The mechanism of action for the treatment of vasomotor symptoms is unknown. Paroxetine, a phenylpiperidine derivative, was originally developed in 1975 by Jorgen Buus-Lassen and associates working in a small Danish company Ferrosan. Paroxetine was the second SSRI synthesized by Buus-Lassen In 1975.

Sertraline (trade names Zoloft and others) is an antidepressant of the selective serotonin reuptake inhibitor (SSRI) class. Sertraline is primarily prescribed for major depressive disorder in adult outpatients as well as obsessive-compulsive disorder, panic disorder, and social anxiety disorder, in both adults and children. The exact mechanism of action sertraline is not fully known, but the drug appears to selectively inhibit the reuptake of serotonin at the presynaptic membrane. This results in an increased synaptic concentration of serotonin in the CNS, which leads to numerous functional changes associated with enhanced serotonergic neurotransmission. It is suggested that these modifications are responsible for the antidepressant action observed during long-term administration of antidepressants. It has also been hypothesized that obsessive-compulsive disorder is caused by the dysregulation of serotonin, as it is treated by sertraline, and the drug corrects this imbalance. Compared to other SSRIs, sertraline tends to be associated with a higher rate of psychiatric side effects and diarrhea. It tends to be more activating (that is, associated with a higher rate of anxiety, agitation, insomnia, etc.) than other SSRIs, aside from fluoxetine. Over a two-week treatment of healthy volunteers, sertraline slightly improved verbal fluency but did not affect word learning, short-term memory, vigilance, flicker fusion time, choice reaction time, memory span, or psychomotor coordination. In spite of lower subjective rating, that is, feeling that they performed worse, no clinically relevant differences were observed in the objective cognitive performance in a group of people treated for depression with sertraline for 1.5 years as compared to healthy controls

Clomipramine is an antidepressant drug which was approved by FDA for the treatment of Obsessive-Compulsive Disorder. The exact mechanism of its action is unknown, however it is supposed that it may exert its effect by inhibiting serotonin reuptake.

Fluoxetine hydrochloride is the first agent of the class of antidepressants known as selective serotonin-reuptake inhibitors (SSRIs). Fluoxetine is a racemic mixture of the R- and S- enantiomers and are of equivalent pharmacologic activity. Despite distinct structural differences between compounds in this class, SSRIs possess similar pharmacological activity. As with other antidepressant agents, several weeks of therapy may be required before a clinical effect is seen. SSRIs are potent inhibitors of neuronal serotonin reuptake. They have little to no effect on norepinephrine or dopamine reuptake and do not antagonize α- or β-adrenergic, dopamine D2 or histamine H1 receptors. During acute use, SSRIs block serotonin reuptake and increase serotonin stimulation of somatodendritic 5-HT1A and terminal autoreceptors. Fluoxetine is marketed under the trade names Prozac and Sarafem among others. It is also marketed for the treatment of premenstrual dysphoric disorder (Sarafem®, fluoxetine hydrochloride). PROZAC is a selective serotonin reuptake inhibitor indicated for: • Acute and maintenance treatment of Major Depressive Disorder (MDD) in adult and pediatric patients aged 8 to 18 years • Acute and maintenance treatment of Obsessive Compulsive Disorder (OCD) in adult and pediatric patients aged 7 to 17 years • Acute and maintenance treatment of Bulimia Nervosa in adult patients • Acute treatment of Panic Disorder, with or without agoraphobia, in adult patients. Studies at clinically relevant doses in man have demonstrated that fluoxetine blocks the uptake of serotonin into human platelets. Studies in animals also suggest that fluoxetine is a much more potent uptake inhibitor of serotonin than of norepinephrine. Antagonism of muscarinic, histaminergic, and α1-adrenergic receptors has been hypothesized to be associated with various anticholinergic, sedative, and cardiovascular effects of classical tricyclic antidepressant (TCA) drugs. Fluoxetine binds to these and other membrane receptors from brain tissue much less potently in vitro than do the tricyclic drugs.

Trazodone (brand name Oleptro, Desyrel, etc) is a serotonin uptake inhibitor that is used as an antidepressive agent. Trazodone binds to the 5-HT2 receptor, it acts as a serotonin agonist at high doses and a serotonin antagonist at low doses. Like fluoxetine, trazodone's antidepressant activity likely results from blockage of serotonin reuptake by inhibiting serotonin reuptake pump at the presynaptic neuronal membrane. If used for long time periods, postsynaptic neuronal receptor binding sites may also be affected. The sedative effect of trazodone is likely the result of alpha-adrenergic blocking action and modest histamine blockade at the H1 receptor. It weakly blocks presynaptic alpha2-adrenergic receptors and strongly inhibits postsynaptic alpha1 receptors. Trazodone does not affect the reuptake of norepinephrine or dopamine within the CNS. Because of its lack of anticholinergic side effects, trazodone is especially useful in situations in which antimuscarinic effects are particularly problematic (e.g., in patients with benign prostatic hyperplasia, closed-angle glaucoma, or severe constipation). Trazodone's propensity to cause sedation is a dual-edged sword. For many patients, the relief from agitation, anxiety, and insomnia can be rapid; for other patients, including those individuals with considerable psychomotor retardation and feelings of low energy, therapeutic doses of trazodone may not be tolerable because of sedation. Trazodone elicits orthostatic hypotension in some patients, probably as a consequence of α1-adrenergic receptor blockade. Mania has been observed in association with trazodone treatment, including in patients with bipolar disorder, as well as in patients with previous diagnoses of major depression. Compared to the reversible MAOI antidepressant drug moclobemide, significantly more impairment of vigilance occurs with trazodone.

Amoxapine is an antidepressant of the dibenzoxazepine class, chemically distinct from the dibenzazepines, dibenzocycloheptenes, and dibenzoxepines. It is designated chemically as 2-Chloro-11- (1-piperazinyl)dibenz[b,f ][1,4]oxazepine. Amoxapine is an antidepressant with a mild sedative component to its action. The mechanism of its clinical action in man is not well understood. In animals, amoxapine reduced the uptake of norepinephrine and serotonin and blocked the response of dopamine receptors to dopamine. Amoxapine is not a monoamine oxidase inhibitor. Amoxapine is absorbed rapidly and reaches peak blood levels approximately 90 minutes after ingestion. It is almost completely metabolized. The main route of excretion is the kidney. In vitro tests show that amoxapine binding to human serum is approximately 90%. In man, amoxapine serum concentration declines with a half-life of eight hours. However, the major metabolite, 8-hydroxyamoxapine, has a biologic half-life of 30 hours. Metabolites are excreted in the urine in conjugated form as glucuronides. Clinical studies have demonstrated that amoxapine has a more rapid onset of action than either amitriptyline or imipramine. The initial clinical effect may occur within four to seven days and occurs within two weeks in over 80% of responders.

Trimipramine is a tricyclic antidepressant similar to imipramine, but with more antihistaminic and sedative properties. It was sold under brand name surmontil for the relief of symptoms of depression. Endogenous depression is more likely to be alleviated than other depressive states. In studies with neurotic outpatients, the drug appeared to be equivalent to amitriptyline in the less-depressed patients but somewhat less effective than amitriptyline in the more severely depressed patients. In hospitalized depressed patients, trimipramine and imipramine were equally effective in relieving depression. Trimipramine has been reported to differ from other typical tricyclic antidepressant drugs in several aspects, for instance it does not inhibit neuronal transmitter uptake and does not cause down-regulation of beta-adrenoceptors. Moreover, it may possess antipsychotic activity in schizophrenic patients. In addition, was found that it did not antagonize the inhibitory effect of noradrenaline and 5-hydroxytryptamine on the release of transmitter, mediated by presynaptic auto receptors. In radioligand binding studies, trimipramine showed fairly high affinities for some dopamine (DA), noradrenaline and 5-hydroxytryptamine (5-HT) receptor subtypes (5-HT2 receptors = alpha 1A/B-adrenoceptors greater than or equal to D2 receptors), intermediate affinities for D1 receptors, alpha 2B-adrenoceptors and 5-HT1C receptors but only low affinities for alpha 2A-adrenoceptors, 5-HT1A, 5-HT1D and 5-HT3 receptors. It may thus be classified as an atypical neuroleptic drug.

Protriptyline (trade name Vivactil) is a tricyclic antidepressant, indicated for the treatment of depression. Protriptyline acts by decreasing the reuptake of norepinephrine and to a lesser extent serotonin (5-HT) in the brain. Tricyclic antidepressants act to change the balance of naturally occurring chemicals in the brain that regulate the transmission of nerve impulses between cells. Protriptyline increases the concentration of norepinephrine and serotonin (both chemicals that stimulate nerve cells) and, to a lesser extent, blocks the action of another brain chemical, acetylcholine. The therapeutic effects of protriptyline, like other antidepressants, appear slowly. Maximum benefit is often not evident for at least two weeks after starting the drug. Protriptyline is used primarily to treat depression and to treat the combination of symptoms of anxiety and depression. Like most antidepressants of this chemical and pharmacological class, protriptyline has also been used in limited numbers of patients to treat panic disorder, obsessive-compulsive disorder, attention-deficit/hyperactivity disorder, enuresis, eating disorders such as bulimia nervosa, cocaine dependency, and the depressive phase of bipolar disorder (manic-depressive) disorder. It has also been used to support smoking cessation programs. Like all tricyclic antidepressants, protriptyline should be used cautiously and with close physician supervision. This is especially so in the elderly, or people who have benign prostatic hypertrophy (enlarged prostate gland), or urinary retention, or glaucoma, especially angle-closure glaucoma (the most severe form). Before starting treatment, people should discuss the relative risks and benefits of treatment with their doctors to help determine if protriptyline is the right antidepressant for them. A common problem with tricyclic antidepressants is sedation (drowsiness, lack of physical and mental alertness), but protriptyline is considered the least sedating agent among this class of agents. Its side effects are especially noticeable early in therapy. In most people, early tricyclic side-effects decrease or disappear entirely with time, but, until then, patients taking protriptyline should take care to assess which side-effects occur in them and should not perform hazardous activities requiring mental acuity or coordination. The side-effects are increased when protriptyline is taken with central nervous system depressants, such as alcoholic beverages, sleeping medications, other sedatives, or antihistamines, as well as with other antidepressants including SSRIs, SNRIs or monoamine oxidase Inhibitors.

Nortriptyline is a second-generation tricyclic antidepressant (TCA) marketed as the hydrochloride salt under the trade names Sensoval, Aventyl, Pamelor, Norpress, Allegron, Noritren and Nortrilen. Nortriptyline is used in the treatment of depression and childhood nocturnal enuresis. Its off-label uses include treatment of postherpetic neuralgia, angioedema and smoking Cessation, and attention deficit hyperactivity disorder in some neurological disorders. It is believed that nortriptyline either inhibits the reuptake of the neurotransmitter serotonin at the neuronal membrane or acts at beta-adrenergic receptors. Nortriptyline is US FDA-approved for the treatment of major depression. In the United Kingdom, it may also be used for treating nocturnal enuresis, with courses of treatment lasting no more than three months. The most common side effects include dry mouth, sedation, constipation, and increased appetite, mild blurred vision, tinnitus, occasionally hypomania or mania. An occasional side effect is a rapid or irregular heartbeat. Alcohol may exacerbate some of its side effects. However, fewer and milder side effects occur with nortriptyline than tertiary tricyclic antidepressants such as imipramine and amitriptyline. For this reason, nortriptyline is preferred to other tricyclic antidepressants, particularly with older adults, which also improves compliance.