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Venlafaxine XL for the treatment of cataplexy in narcolepsy

What is cataplexy in narcolepsy?

Narcolepsy is a long-term condition which causes excessive sleepiness during the day and may disrupt your sleep at night. You can also have sleep attacks where you fall asleep at inappropriate times during the day without any warning.

Cataplexy is a condition associated with narcolepsy that results in sudden muscle weakness. This can be triggered by strong emotions such as:

  • laughter
  • anger
  • fright
  • surprise

Muscle weakness can vary in severity, and cataplexy attacks can differ in both type and how long they last for.

What is venlafaxine XL?

Venlafaxine XL belongs to a group of medicines called anti-depressants. It can be used to treat cataplexy in narcolepsy and works by interfering with certain chemicals in the brain which may be involved in causing the symptoms of cataplexy.

Venlafaxine XL is an ‘extended release’ medication. Extended release medications release the medication slowly over 24 hours so they last longer.

This will help stop severe cataplexy attacks. This is when you have cataplexy attacks repeatedly for hours or days without a rest period, and without emotional triggers.

Severe cataplexy attacks can develop if you stop venlafaxine XL suddenly or if you switch to a different version which does not last 24 hours.

Taking an unlicensed medicine

Taking venlafaxine XL for narcolepsy treatment is unlicensed. This means the manufacturer of the medicine has not specified that it can be used in this way. However there is evidence that it works to treat this particular condition.

How do I take the medicine?

For the treatment of cataplexy, venlafaxine XL should be taken in the following way

  • Take once a day, in the morning.
  • You can be take them with or without food.
  • Swallow the tablet whole with a drink of water.
  • Do not chew or crush them.

Keep taking the medicine until your consultant tells you otherwise. Stopping suddenly can cause side effects such as:

  • repeated cataplexy
  • feeling and being sick
  • anxiety
  • headaches
  • sleep disturbances

Your consultant will want you to reduce your dose gradually if you need to stop treatment.

What should I do if I forget to take the medicine?

Do not take a double dose to make up for a missed dose as this is too much to take at one time.

If you forget to take the dose in the morning, don’t worry and take it as soon as you remember. Try not to take venlafaxine XL within the 2 hours before your bedtime as your sleep may be disrupted. In this case, do not take the dose and wait until the next morning for your usual dose.

Missing a dose of venlafaxine XL can cause severe cataplexy attacks.

Are there any side effects?

Most medicines can cause unwanted side effects, although not everyone gets them. The following are examples of some of the side effects reported by patients taking venlafaxine XL. The unwanted effects often fade as your body adjusts to the new medicine, but speak with your GP or pharmacist if any of the following continue or become troublesome.

Side effect

What should I do if it happens?

Very common (more than 10 percent)
Headache Drink plenty of water and take your usual painkiller, for example, paracetamol. If the headache continues, speak with your GP.
Dry mouth Try chewing sugar-free gum or sucking sugar-free sweets.
Feeling and being sick Stick to simple foods. Try taking your doses after meals if you are not already doing so.
Sweating Take care not to become overheated during exercise or hot weather.
Common (between 1 percent and 10 percent)
Feeling dizzy, tired or sleepy Do not drive or use tools or machinery until you feel better. Do not drink alcohol.
Constipation Try to eat a well-balanced diet containing plenty of fibre and drink plenty of water each day.
Uncommon (between 0.1 percent and 1 percent)
Loss of weight or appetite

Sleeping problems, yawning

Tingling feelings

Feeling nervous or confused

Eyesight problems

Chills, hot flushes

Difficulties having sex

Raised cholesterol

Menstrual problems

If any of these become troublesome, speak with your GP or consultant.

For further information on side effects, please see the manufacturer’s leaflet that comes with the medicine.


If you experience any of the following symptoms, contact your GP for advice as soon as possible: any changes to your mood, behaviour, or thinking, any suicidal thoughts, or thoughts about harming yourself.

Can I take venlafaxine XL with other medicines?

Venlafaxine XL may interact with some medicines. It is important to let us know about any medicines that you are currently taking, so that we can check venlafaxine XL is suitable for you.

If you are buying any medicines over the counter from a pharmacy, always mention that you have been prescribed venlafaxine XL.

It is safe to take paracetamol with this medicine but always ask your pharmacist for advice before buying any anti-inflammatory painkillers, such as ibuprofen or aspirin.

Seek advice when buying herbal or homeopathic remedies.

How will my treatment be reviewed?

Your treatment will be reviewed on an ongoing basis in the Narcolepsy Clinic and the dose adjusted in response to your symptoms. Your consultant will want to check to make sure that the treatment is helping. You may need to have your blood pressure and heart rate checked regularly.

How do I get a repeat prescription?

Your GP will give you a repeat prescription for venlafaxine XL. Please make sure you request your repeat prescription early to prevent you running out or risk missing any doses of your medication.

If your GP won’t supply your venlafaxine XL, your consultant will provide repeat prescriptions, which will be sent in the post. It can also be dispensed by the Rowland’s pharmacy at Sheffield Children’s hospital outpatients on 0114 305 3367.

Is there anything else I need to know?

It can take 1 or 2 weeks after starting this treatment before the effect builds up, and up to 4 weeks before you feel the full benefit. It is important that you continue taking the medicine, even if you feel that it is not helping you.


Venlafaxine XL can make your skin more sensitive to sunlight. Try to avoid strong sunlight, and use a sun cream with a high protection factor.

❌ Do not use sunbeds.


Venlafaxine XL can alter the levels of sugar in your blood. If you have diabetes you may need to check your blood sugar more regularly. Your GP can advise you about this.


❌ Do not drink alcohol while you are taking venlafaxine XL. Mixing alcohol with venlafaxine XL may increase the risk of other side effects such feeling or being sick, and may worsen any dizziness or drowsiness.


If you are old enough to drive, you must let the Driver and Vehicle Licensing Authority (DVLA) know if you are diagnosed with narcolepsy.

You may be allowed to drive again when your symptoms are well controlled with medication, but you will need to have regular reviews. Your consultant will advise you about this.

If you are a driver, please be aware that venlafaxine XL may affect your reactions and ability to drive. It is an offence to drive while your reactions are impaired. Even if your driving ability is not impaired, if you drive, you should carry some evidence with you which shows that the medicine has been prescribed for you. A repeat prescription form or the patient information leaflet from the packet is generally enough.

Pregnancy and breastfeeding

If you are considering becoming pregnant, or have discovered you are pregnant, you should discuss this with your consultant as soon as possible so that a management plan can be agreed. We do not recommend taking it while breastfeeding.

Sleep routine

Taking venlafaxine XL is not a replacement for a good sleep routine. It is still important to aim to get around 9 to 11 hours of sleep at night, depending on your age. Try to go to bed when tired and get up at about the same time each day.

Venlafaxine XL should be kept out of reach of children. If anyone other than you takes this medicine, you, they, or their parent or carer should contact NHS 111 for advice. If they are unwell they should call for an ambulance.


Do not use the medicine after the expiry date.

The expiry date is printed on the container. Any that have gone out of date should be returned to your local pharmacy to be properly disposed of.

Contact us

Medicines Helpline

If you have any questions or concerns about your medicines, please speak to the staff caring for you or call our pharmacy helpline.

Narcolepsy team secretaries

0114 271 7400 between 9am to 5pm, Monday to Friday.

Rowland’s Outpatient pharmacy

0114 305 3367 between 9am to 5pm, Monday to Friday.

Your comments and concerns

For advice, support or to raise a concern, contact our Patient Advice and Liaison Service (PALS) on 0114 271 7594 or email scn-tr.pals@nhs.net.
To make a complaint, contact the complaints department on 0114 271 7194.

Other resources

Narcolepsy UK
You might find this charity’s website useful for connecting with patients who suffer from the same condition as you, but any information found should not alter your current treatment. You should discuss any new advice with the doctor caring for your condition.

NHS 111
Offers medical help and advice from fully trained advisers supported by experienced nurses and paramedics. Available over the phone 24 hours a day on 111.

Provides online information and guidance on all aspects of health and healthcare, to help you make choices about your health.


Reproduced with the kind permission of Guy’s and St Thomas’ NHS Foundation Trust.

Is something missing from this resource that you think should be included? Please let us know

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Please note: this is a generic information sheet relating to care at Sheffield Children’s NHS FT. These details may not reflect treatment at other hospitals. This information is not intended as a substitute for professional medical care. Always follow your healthcare professionals’ instructions. If this resource relates to medicines, please read it alongside the medicine manufacturer’s patient information leaflet. If this information has been translated into another language from English, efforts have been made to maintain accuracy, but there may still be some translation errors. If you are unsure about any of the guidance in this resource or have specific questions about how it relates to your child, always ask your healthcare professional for further advice.

Resource number: SLP30

Resource Type: Article

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