Venlafaxine, sold under the brand name Effexor among others, is an antidepressant medication of the serotonin–norepinephrine reuptake inhibitor (SNRI) class.

[9] Studies have shown that venlafaxine improves post-traumatic stress disorder (PTSD) as a recommended first-line treatment.

[7] Common side effects include loss of appetite, constipation, dry mouth, dizziness, sweating, insomnia, drowsiness and sexual problems.

[17] It has also been found to reduce the severity of 'hot flashes' in menopausal women and men on hormonal therapy for the treatment of prostate cancer.

[18][19] Due to its action on both the serotoninergic and adrenergic systems, venlafaxine is also used as a treatment to reduce episodes of cataplexy, a form of muscle weakness, in patients with the sleep disorder narcolepsy.

[20] Some open-label and three double-blind studies have suggested the efficacy of venlafaxine in the treatment of attention deficit-hyperactivity disorder (ADHD).

[22] Case reports, open trials and blinded comparisons with established medications have suggested the efficacy of venlafaxine in the treatment of obsessive–compulsive disorder.

Venlafaxine is not recommended in patients hypersensitive to it, nor should it be taken by anyone who is allergic to the inactive ingredients, which include gelatin, cellulose, ethylcellulose, iron oxide, titanium dioxide and hypromellose.

[2][6][37] Venlafaxine might interact with tramadol or other opioids, as well as trazodone, so caution is needed while mixing multiple serotonergic agents together.

[40] In a study sponsored by Wyeth, which produces and markets venlafaxine, the data on more than 200,000 cases were obtained from the UK general practice research database.

A statistically significant greater risk for attempted suicide remained after adjustment, but the authors concluded that it could be due to residual confounding.

[41] An analysis of clinical trials by the FDA statisticians showed the incidence of suicidal behaviour among the adults on venlafaxine to be not significantly different from fluoxetine or placebo.

[citation needed] Serotonin syndrome symptoms may include mental status changes (e.g. agitation, hallucinations, coma), autonomic instability (e.g. tachycardia, labile blood pressure, hyperthermia), neuromuscular aberrations (e.g. hyperreflexia, incoordination), or gastrointestinal symptoms (e.g. nausea, vomiting, diarrhea).

[45] A case of a patient with serotonin syndrome induced by low-dose venlafaxine (37.5 mg per day) has also been reported.

A study released in May 2010 by the Canadian Medical Association Journal suggests use of venlafaxine doubles the risk of miscarriage.

[51] As with other serotonin reuptake inhibitors (SRIs), these effects are generally short-lived, lasting only 3 to 5 days,[52] and rarely resulting in severe complications.

Because venlafaxine appears to be more likely than SSRIs and bupropion to induce mania and mixed episodes in these patients, provider discretion is advised through "carefully evaluating individual clinical cases and circumstances."

[57] It is usually reserved as a second-line treatment for depression due to a combination of its superior efficacy to the first-line treatments like fluoxetine, paroxetine and citalopram and greater frequency of side effects like nausea, headache, insomnia, drowsiness, dry mouth, constipation, sexual dysfunction, sweating and nervousness.

Forced diuresis, hemodialysis, exchange transfusion, or hemoperfusion are unlikely to be of benefit in hastening the removal of venlafaxine, due to the drug's high volume of distribution.

[62] Venlafaxine has a higher rate of moderate to severe withdrawal symptoms relative to other antidepressants (similar to the SSRI paroxetine).

It is extensively metabolized in the liver via the CYP2D6 isoenzyme to desvenlafaxine (O-desmethylvenlafaxine, now marketed as a separate medication named Pristiq[83]), which is just as potent an SNRI as the parent compound, meaning that the differences in metabolism between extensive and poor metabolisers are not clinically important in terms of efficacy.

[6] The half-life of venlafaxine is relatively short, so patients are directed to adhere to a strict medication routine, avoiding missing a dose.

The gene encoding P-gp, ABCB1, has the SNP rs2032583, with alleles C and T. The majority of people (about 70% of Europeans and 90% of East Asians) have the TT variant.

A 2007 study[88] found that carriers of at least one C allele (variant CC or CT) are 7.72 times more likely than non-carriers to achieve remission after 4 weeks of treatment with amitriptyline, citalopram, paroxetine or venlafaxine (all P-gp substrates).

Studies have shown that the extended-release formula has a lower incidence of nausea as a side effect, resulting in better compliance.