Effexor Half-Life: How Long Does Venlafaxine Stay In Your System?

Last Updated: March 25, 2024

Nena Messina Authored by Nena Messina, Ph.D.
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Individual factors such as age, genetics, liver and renal function, and dosing play a critical role in how long Effexor stays in the system. There is a difference in Effexor half-life of immediate-release and extended-release formulations. So, what is the Effexor mechanism of action? How long does it take for Effexor to get out of your system?

Venlafaxine Absorption And Metabolization

The drug dosage is taken orally and absorbed from the gastrointestinal tract into the bloodstream. The sustained-release tablet is more slowly absorbed than immediate-release venlafaxine tablets. About 92% of the Effexor dosage is absorbed orally.

After absorption, the substance undergoes extensive first-pass metabolism in the liver to its major metabolite, O-desmethylvenlafaxine, and two minor metabolites N-desmethylvenlafaxine and N, O-didesmethyl venlafaxine. CYP2D6 enzyme is responsible for metabolism to O-desmethylvenlafaxine. While CYP3A4, CYP2C19, and CYP2C9 enzymes are responsible for its metabolism to N-desmethylvenlafaxine. O-desmethylvenlafaxine possesses antidepressant activity that is comparable to that of venlafaxine.

Female hands holding one Effexor pill.

Effexor and its metabolites are primarily excreted via the kidneys. The drug is excreted as 5% unchanged venlafaxine, 55% O-desmethylvenlafaxine, and 27% other minor inactive metabolites.

Effexor Mechanism Of Action

Venlafaxine is an SSRI that blocks the transporters responsible for the reuptake of norepinephrine and serotonin. Venlafaxine MOA is by offering the antidepressant effect by potentiating the neurotransmitter activity in the central nervous system. This process takes place by inhibiting the reuptake of serotonin and norepinephrine, as mentioned above. The Effexor mechanism of action occurs without the various cardiovascular, sedative, and anticholinergic effects seen in other drugs in this class.

If the recommended medication dosage is the right one, the patient should feel an improvement in energy levels, mood, and interest in daily living. Feeling of anxiety and fear or unwanted thoughts should decrease, as well as panic attacks. The patient should note that the treatment must not be stopped even if the depression improves.

The two main signs that the Venlafaxine MOA takes place are the decrease or lack of thoughts of self-harm and teariness. Later on, the patient will be more tolerant; little things will not irritate them anymore, and they will have more sense of enjoyment.

How Long Does It Take For Effexor To Work?

Full effects of immediate-release tablets are seen two to three hours after ingestion if taken at regular intervals. The effects of venlafaxine extended-release are felt five to nine hours after ingestion, with standard dosages.

Patient taking a medicine and holding a blister.

How long does it take for Effexor to work for depression? The first effects on depression are seen two to four weeks when the patient should experience a decrease in depressive symptoms. The drug reaches its maximum efficacy after eight weeks. Some patients might experience an increase in anxiety at the beginning of the treatment, a possible result of the drug’s mechanism of action, which will start to decrease in the following weeks. The pills should be taken for several months to avoid depression relapse. The frequency of intake is determined in conformity with Effexor half-life. Therefore, skipping doses is not recommended as it can provoke Venlafaxine withdrawal symptoms. The treatment for depression usually lasts for six months and generalized anxiety disorder for around 18 months.

How Long Does Effexor XR Stay In Your System?

There are two formulations of the medication: immediate-release and extended-release. There is a difference between Effexor half-life depending on the formulation. The immediate-release elimination half-life is about 5 hours, while the elimination half-life of Effexor XR is about 11 hours.

How long does it take for Effexor to get out of your system? Some patients may excrete the medication in just 16.5 hours, while it may take 1.6 days for others to completely excrete it.

Will venlafaxine show on a drug test? Effexor drug tests fall basically into two categories, screening tests and confirmatory tests. Due to the lack of screening tests specificity for this drug, confirmatory tests will distinguish venlafaxine from other medications.

Time Of Staying In Urine

Effexor may show up on a urine drug test after 48 hours of its administration. A false-positive urine immunoassay screening tests for phencyclidine and amphetamine have been reported. This is due to the lack of specificity of the screening tests. False-positive test results may be expected for several days following venlafaxine stopping. Gas chromatography and mass spectrometry are confirmatory drug tests that will distinguish venlafaxine from phencyclidine.

Time Of Staying In Blood

Steady-state concentrations of venlafaxine in plasma are attained within three days of oral multiple-dose therapy. As a result, blood samples may be collected within 72 hours for the estimation of venlafaxine.

Time Of Staying In Hair

According to a study published in the US National Library of Medicine, antidepressants can be detected in the hair follicle for at least 16 months after intake. As a result, venlafaxine also may be detected after about 1.5 years of its intake.

How Long Does Effexor Stay in Your System?

Factors Influencing Time Of Venlafaxine Stay In System

The average clearance of the drug occurs within 48 hours after administration. However, certain factors may affect Effexor half-life. It takes about 3 to 4 days for Effexor to leave the body completely. Others may excrete the medication in a much shorter duration. Several individual variables should be considered when contemplating how long the drug lasts in the body.

Individual Features

Individual factors play a crucial role in how long Effexor XR lasts in the system. Two persons may not clear it at the same time.

Patient Age

Several age-related factors may prolong venlafaxine excretion time. The elderly with restricted hepatic blood flow and decreased kidney functions may have a prolonged excretion of the drug. The elimination half-life of Effexor is more extended in neonates than adults, ranging between 12 and 15 hours. The steady-state venlafaxine’s half-life is increased in the elderly than the younger persons by 24%.

Patient’s Body Mass And Fats

A person’s body mass and fat percentage may affect medication metabolism and excretion. The persons with a small body mass who take venlafaxine may excrete it slowly as they ingested a greater quantity of the medication relative to their body size. On the other hand, the one with greater body mass may excrete it quickly.


Effexor mechanism of action and its metabolism and excretion may be affected by genetic variations. A patient with poor medication metabolism has prolonged clearance time. According to the National Center for Biotechnology Information, patients who carry two inactive copies of CYP2D6 “poor metabolizers” may have decreased capacity for metabolization of the substance. It leads to less active metabolites in their body. On the other hand, those who carry more than two copies of functional CYP2D6 alleles “ultrarapid metabolizers” may have an increased capacity for its metabolism, leading to more active metabolites in their bodies.

Renal And Hepatic Functions

The elimination half-life of Effexor is usually prolonged in patients with liver problems. A patient with hepatic fibrosis or cirrhosis generally retains the medication in the body more than those with normal hepatic functions.

PH Of Urine

A low PH of urine (acidic urine) will accelerate the drug’s excretion out of the system. In contrast, high PH of urine (alkaline urine) would help in venlafaxine reabsorption from the urinary bladder into the blood again. As a result, alkaline urine would retain the medication in the body more than acidic urine.

Dose Taken

A patient who takes low doses of the medication would metabolize and excrete it quickly. For instance, patients who take a dose of venlafaxine tablets at 37.5 mg daily would likely metabolize and eliminate it faster than those who take venlafaxine ER 150mg capsules.

An overdose on Effexor can be dangerous as the drug is accumulated throughout the body, while a kidney can only excrete a certain amount of it at that time.

Mixing With Other Drugs

Mixing this antidepressant with other medications may cause an increase or decrease in venlafaxine concentration in the blood. Dangerous venlafaxine drug interactions occur when a person combines it with CYP2D6 enzyme inhibitors such as Fluoxetine, Paxil, and bupropion.

Various tablets and capsules in blisters on the table.

Mixing can prolong the clearance time of venlafaxine as enzyme inhibitors decrease its metabolism and excretion. Mixing CYP2D6 enzyme inducers such as Haloperidol, Glutethimide, and Rifampin with Effexor can lower their blood concentration as these medications accelerate venlafaxine metabolism and excretion. As a result, the therapeutic efficacy of the medication was decreased when it was mixed with CYP2D6 inducer.

Frequency Of Use

A high frequency of venlafaxine use at greater than recommended doses may increase drug concentration in the body. Therefore, the side effects of Effexor may appear. On the other hand, those who take it irregularly or intermittently are less likely to attain peak concentration of the drug throughout the system. In this case, the medicine may be ineffective in treating depression.

Clear the Medication From System Safely

It is highly recommended not to use any additional substances to speed up this process as dangerous health complications may occur. Any attempts to falsify the drug test results also may lead to legal liability. The best way to stop venlafaxine safely is to do it gradually and enroll in a rehab center for medical detoxification. Stopping this medication suddenly without doctor’s consultation may increase the risk of withdrawal side effects.

If there is a need to stop drug use, a doctor may also consider the difference between Prozac and Effexor or other drugs for anxiety and depression to choose an alternative medication.

An addiction may occur when a person continues to misuse a drug. Treating addiction to Effexor as soon as possible helps to get rid of adverse health complications.

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Page Sources

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Published on: November 29th, 2019

Updated on: March 25th, 2024

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