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Rx pill bottle and prescription pad: Venlafaxine side effects and how to avoid them
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Venlafaxine side effects and how to avoid them

Venlafaxine side effects include sexual dysfunction, weight changes, urinary retention and sleepiness
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By | Oct. 13, 2022 Medically reviewed by Anne Jacobson, MD, MPH

Common venlafaxine side effects | Serious side effects | Sexual dysfunction | Weight changes | Urinary retention | Sleepiness | Side effects timeline | Contraindications | Warnings | Interactions | How to avoid side effects | How to treat side effects

Venlafaxine, also sold as brand-name Effexor XR, is an antidepressant that is FDA-approved to treat major depressive disorder (MDD), generalized anxiety disorder, social anxiety disorder, and panic disorder. It is also prescribed off-label for post-traumatic stress disorder (PTSD), migraines, and nerve pain. 

Venlafaxine belongs to a family of drugs called serotonin-norepinephrine reuptake inhibitors or SNRIs. These drugs increase the concentration of certain chemicals that pass signals between nerves (called neurotransmitters). This mechanism essentially activates the parts of the brain that help with mood control. Changing the way the nervous system works has benefits for many people, but may also produce a variety of unwanted side effects. 

Common side effects of venlafaxine

Nausea is the most common side effect of venlafaxine. About 30% to 60% of people on venlafaxine feel queasy or nauseous, especially when first starting the medication.. Common side effects of venlafaxine include:

  • Nausea
  • Headache
  • Trouble sleeping
  • Drowsiness
  • Dry mouth
  • Dizziness
  • Sweating
  • Ejaculation problems
  • Weakness
  • Weight loss
  • Loss of appetite
  • Constipation
  • Elevated blood pressure
  • Impotence
  • Yawning
  • Diarrhea
  • Decreased interest in sex
  • Indigestion
  • Anxiety
  • Tremor
  • Infection
  • Orgasm problems
  • Agitation
  • Vomiting
  • Flushing
  • Blurred vision
  • Strange dreams
  • Fast or irregular heart beats
  • High cholesterol
  • Numbness or tingling

Serious side effects of venlafaxine

The most serious side effects of venlafaxine are:

  • Suicidal thoughts and behaviors
  • Worsening of depression
  • Mania or hypomania
  • Seizures
  • Serotonin syndrome
  • Heart rhythm abnormalities
  • Drug-induced involuntary movement problems
  • Swollen pancreas
  • Liver poisoning
  • Low sodium
  • Angle-closure glaucoma
  • Bleeding
  • Blood problems
  • High blood pressure (hypertension)
  • Lung disease
  • Withdrawal if stopped suddenly
  • Growth suppression (in children)
  • Severe allergic or skin reactions
  • Muscle tremors, movements, or contractions
  • Heart failure

Sexual dysfunction

Sexual problems are commonly experienced by people taking antidepressants. Up to 67% of people taking venlafaxine may experience sexual dysfunction symptoms. These issues may include ejaculation problems, erectile dysfunction, loss of sexual drive, and problems reaching orgasm. Fortunately, most people will see a return to normal sexual functioning when the drug is stopped. If sexual function is a problem, talk to the prescribing healthcare provider.

Weight changes

Weight loss is a common problem in children taking venlafaxine. In clinical trials, 18% to 47% of pediatric participants lost weight on venlafaxine depending on the dose and the condition being treated. Children on venlafaxine also gained less height than those receiving a placebo. Although appetite loss is a common side effect, healthcare professionals do not believe venlafaxine-induced weight loss is related to decreased appetite. Children, particularly those younger than 12, will need to be monitored for both height and weight when taking venlafaxine.

Urinary retention

Urinary retention is a rare side effect of venlafaxine, occurring in less than one percent of patients. People taking venlafaxine may also urinate more than usual or experience urinary urgency or incontinence. These problems can manifest early on in treatment, so tell the prescribing healthcare provider about the problem.

Sleepiness

It’s fairly common to feel sleepy when taking certain antidepressants. For venlafaxine, 15% of people taking the drug felt drowsy, but the rate could be as high as 23%. If sleepiness, fatigue, or tiredness is interfering with daily functioning, get medical advice from the prescribing healthcare provider.

How soon do venlafaxine side effects start?

Some common venlafaxine side effects such as drowsiness, nausea, headache, sleeplessness, and dry mouth can start shortly after starting treatment. Allergic reactions could start within minutes. Side effects such as weight loss, sexual dysfunction, appetite loss, and many of the most serious side effects don’t usually begin until after several weeks of treatment.

How long do venlafaxine side effects last?

Many of the most common side effects of venlafaxine become milder as the body adapts to the medicine. Some, however, may not get better until the medicine is stopped. Once it’s stopped, most adverse effects should start clearing up by the next day. Some side effects, particularly the more severe ones, may cause long-term problems. 

What are the long-term side effects of venlafaxine?

For adults, venlafaxine is safe to take for a long time. Doing so does not produce unique side effects, but it is more likely to cause withdrawal symptoms if discontinued suddenly. Most side effects of venlafaxine do not persist for long after the drug has stopped. However, some serious side effects, such as heart problems, lung disease, or glaucoma, could have long-term consequences.

Venlafaxine contraindications

Venlafaxine is contraindicated in people with a known history of allergic reactions to venlafaxine or a similar drug, Pristiq (desvenlafaxine). It should also not be taken by people who have taken a category of antidepressants called MAO inhibitors within the last 14 days.

Pregnancy

The risk of fetal harm is low if taking venlafaxine during pregnancy. If taken in the last three months of pregnancy, a newborn baby may experience withdrawal or serotonin syndrome. There may also be increased bleeding after delivery.

Breastfeeding

The risk to a nursing infant is low. However, venlafaxine is present in breast milk, so talk with your healthcare provider about risks and benefits if you are breastfeeding.

Children

The Food and Drug Administration (FDA) has not approved the use of venlafaxine for anyone younger than the age of 18. It is sometimes used to treat mental health conditions in some children. However, there is a risk of worsening depression, suicidality, weight loss, and growth suppression in children and adolescents given venlafaxine.

Venlafaxine warnings

Though only contraindicated for people with hypersensitivity to venlafaxine, that doesn’t mean the drug is completely safe for everyone else. Because of potential problems, some situations may be riskier than others.

Black box warning

Like other antidepressants, venlafaxine contains an FDA-mandated black box warning about the risk of worsening depression and suicidality in children, teens, and young adults given the medicine. 

Cautions

Existing health conditions may be worsened by venlafaxine, so healthcare professionals are advised to be cautious, monitor for problems, and sometimes adjust doses for people with: 

  • Heart problems: People with irregular heartbeats, a personal or family history of some kinds of EKG changes, congestive heart failure, or a recent heart attack may require regular monitoring while taking venlafaxine.
  • Bleeding disorders: Venlafaxine can slow down blood clotting, a side effect that will worsen pre-existing bleeding problems.
  • Bipolar disorder: Venlafaxine can bring on mania or hypomania. 
  • History of seizures: Venlafaxine can bring on seizures in people who are already at risk for seizures.
  • Uncorrected narrow angles: Angle-closure glaucoma, an eye problem that rapidly progresses to vision loss and blindness, has been reported in people taking venlafaxine. Uncorrected narrow angles are the primary risk factor for angle-closure glaucoma.
  • High blood pressure can be worsened by venlafaxine.
  • Dehydration puts people at risk for low sodium if they’re on venlafaxine.
  • Electrolyte imbalance
  • Liver impairment
  • Kidney dysfunction
  • Overactive thyroid
  • Seniors: Older adults have a potentially greater risk of side effects, low sodium, or weight loss.
  • Young adults: People younger than 25 years of age have a heightened risk of worsening depression and suicidality when taking venlafaxine.

Abuse and dependence

Venlafaxine is not a controlled substance. The FDA does not consider venlafaxine as having a risk for abuse. It does not create physical dependence. However, sudden discontinuation of the drug could result in withdrawal symptoms.

Overdose

A venlafaxine overdose will require immediate treatment, particularly if the medicine is taken with alcohol or other CNS depressants. For adults, the dose should not exceed 225 mg per day.

Venlafaxine interactions

As a drug that primarily affects the brain, venlafaxine has several potential drug interactions.

Contraindications

Venlafaxine can change the way the heart beats. Some drug interactions can amplify this effect, raising the risk of serious heart problems. For this reason, venlafaxine is never combined with:

It is also never combined with monoamine oxidase inhibitors (MAOIs) because of the risk of serotonin syndrome or other severe side effects. These drugs must be stopped 14 days before taking venlafaxine:

Other drug interactions may have other risks, but the combination isn’t prohibited. The combination can raise the risk of several health problems, including:

  • Increased risk of heart problems
  • Heart rate or heart rhythm drugs
  • Increased risk of serotonin syndrome
  • Increased risk of bleeding episodes
  • Blood thinners such as warfarin
  • Nonsteroidal anti-inflammatory drugs (NSAIDs) 
  • Dietary supplements such as garlic and krill oil
  • Increased risk of side effects in general

How to avoid venlafaxine side effects

Even though venlafaxine’s side effects are common, there are ways to minimize the problems.

1. Tell the prescriber about all medical conditions

The prescribing healthcare provider needs to have a complete medical history. In particular, make sure the prescriber knows about: 

  • Heart problems
  • Seizure problems
  • Bipolar disorder
  • Diabetes
  • Liver disease
  • Kidney disease
  • Thyroid problems
  • High blood pressure
  • Low sodium
  • High cholesterol

2. Tell the prescriber about any drugs being taken

Another source of serious problems is drug interactions. The prescriber needs to know all the drugs being taken regularly. That includes over-the-counter drugs and dietary supplements. These are the most important:

  • MAO inhibitors
  • Antidepressants, anxiety drugs, antipsychotics, bipolar medications, or similar psychiatric drugs
  • Amphetamines
  • Migraine medications such as sumatriptan
  • Opioids like tramadol or fentanyl
  • Blood thinners such as warfarin
  • Histamine blockers such as Tagamet (cimetidine)
  • Supplements or herbal remedies like St. John’s wort or tryptophan.

3. Take venlafaxine as directed

Follow all the instructions given by the prescribing healthcare provider or printed on the prescription label or medication guide. The dosing schedules will be different depending on the format prescribed: venlafaxine is taken as either an immediate-release tablet or an extended-release capsule. 

4. Don’t take extra doses to make up for a missed dose

If a dose is missed, take it when remembered. If it’s almost time for the next dose, though, skip the missed dose and take the next dose as scheduled. 

5. Take the dose in the morning

To help prevent insomnia, take each day’s dose early in the morning.

6. Avoid alcohol and other depressants

Alcohol, sedatives, and sleep aids will make some of venlafaxine’s side effects worse including drowsiness and dizziness.

7. Avoid aspirin and ibuprofen

To prevent problems with bleeding, stomach pain, and ulcers, avoid NSAIDs when taking venlafaxine. If possible, use acetaminophen instead.

How to treat side effects of venlafaxine

Here are some tips for handling some of the most common or serious problems.

Drowsiness and dizziness

If venlafaxine causes drowsiness or dizziness, the primary goal is to avoid falls and injuries. Stand up slowly, move slowly, and consider removing obstacles on the floor that are dangerous if they’re fallen on. 

Low sodium

When mild, low sodium is unpleasant. However, it can evolve into a serious medical condition. The best advice is to call a healthcare professional. The most common symptoms of low sodium are:

  • Headache
  • Weakness
  • Coordination problems
  • Confusion

If seizures are experienced, go to an emergency room.

Suicidal thoughts and behaviors

Young adults and children are vulnerable to suicidal thoughts and behaviors when taking venlafaxine. Medical help is required before that person can harm themselves. The symptoms to watch out for are: 

  • Attempts at suicide
  • Talking about, thinking about, or planning suicide
  • Talking or thinking about death
  • New or sudden changes in mood or behavior
  • New or worsening depression or anxiety
  • Aggressiveness or hostility
  • Violent behavior
  • Reckless or risky behaviors
  • Unusual behaviors
  • Agitation, restlessness, irritability, or anger
  • Panic attacks
  • Hyperactivity or uncontrolled talking
  • Insomnia

Serotonin syndrome

All antidepressants can cause serotonin syndrome, but it usually requires that similar serotonin-raising drugs be taken. Serotonin syndrome is usually mild, but could rapidly develop into a medical emergency. Serotonin syndrome requires immediate medical help, so look for symptoms such as:

  • Racing heartbeat
  • High or low blood pressure
  • Flushing
  • Agitation
  • Hallucinations
  • Dizziness
  • Fever
  • Sweating
  • Muscle stiffness
  • Seizures or convulsions

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