How it works
What does venlafaxine do?
Venlafaxine is a type of serotonin-noradrenaline reuptake inihibitor (SNRI).
(N.B. Noradrenaline is sometimes known as norepinephrine.)
Research suggests that depression is more likely to occur when the brain doesn’t have enough of the chemicals serotonin (also called ‘5HT’) and noradrenaline.
Nerve endings in the brain release these chemicals and take them back up again after they have targeted their receptors in what is known as a recycling process.
Serotonin-noradrenaline reuptake inhibitors (SNRIs) – like venlafaxine - work by blocking recycling of released serotonin and noradrenaline back into the nerve endings.
This increases the amount of serotonin and noradrenaline, which helps treat the symptoms.
Venlafaxine also works on blocking the recycling of dopamine, adding further to its antidepressant effect.
It is worth noting that as the dose of venlafaxine is increased, it becomes more effective at blocking noradrenaline reuptake. However, its effect on serotonin and dopamine stays much the same.
This means that some people may not get the full benefit of venlafaxine until they are on a higher dose.
How long does venlafaxine take to start working?
Antidepressants like venlafaxine can start to work on depression within the first two weeks of treatment. The extent of any improvements you feel should continue to increase over the following few weeks.
It may take four weeks or longer for you to get the full effect.
For anxiety, antidepressants like venlafaxine can take slightly longer to work. For some people, anxiety briefly increases at the start of treatment, but it does decrease with continued treatment.
To get the best effect, you need to take your venlafaxine every day and give it a chance to work for you.
Your doctor will start with a low dose, which they will increase slowly to a dose that is effective for you. This may take several days or weeks.
How long will I need to take venlafaxine?
You will need to take venlafaxine for several months after you feel better, otherwise your symptoms can come back. For depression this might be for six months, but for other conditions such as generalized anxiety disorder it might be up to 18 months.
If your illness has come back, then you might be advised to keep taking venlafaxine for longer than this.
If you stop taking the venlafaxine too soon, there is more chance that your symptoms will come back.
Discuss with your doctor how long you should take venlafaxine for.
If you have bipolar disorder, it is likely that the doctor will advise for the venlafaxine to be stopped sooner. This is because, in bipolar disorder, there is a risk of your mood becoming too high if an antidepressant is used for too long.
Your dose will need to be reduced gradually to reduce the chance of withdrawal effects when it is stopped (unless you are already on the lowest dose).
Your doctor needs to know if...
You need to talk to your doctor or pharmacist before starting treatment with venlafaxine if you have any of the following:
- eye problems, such as glaucoma (increased pressure in the eye)
- a history of high blood pressure
- a history of heart problems
- a history of seizures (fits)
- a history of low sodium levels in your blood (hyponatraemia)
- a tendency to develop bruises or a tendency to bleed easily (history of bleeding disorders), or if you are taking other medicines that may increase the risk of bleeding like warfarin (used to prevent blood clots)
- a history of, or a family history of, bipolar disorder or mania (feeling over-excited or euphoric)
- a history of aggressive behaviour
- a history of thoughts of harming yourself or taking your own life.
You should only take venlafaxine as agreed with your doctor.
You will get most benefit from your venlafaxine if you take it every day at the dose prescribed by your doctor.
Make sure that you know your dose. If it is not written on the label, check with your pharmacist or doctor.
You will usually take it once a day (if you take the modified-release or prolonged-release tablets) or twice a day (if it is the plain tablets).
You will usually start with a low dose that your doctor will gradually increase to a dose that is effective for you. This may take several weeks.
Choose a time of the day to take venlafaxine that you can always remember. As venlafaxine should be taken with food, this could be a mealtime or when you have a snack.
Take venlafaxine with food.
Swallow the tablet whole with a glass of water - it tastes bitter if you chew it.
If you find it difficult to take it more than once a day, ask your doctor about the long-acting tablets or capsules because they only need to be taken once a day.
Swallow the long-acting tablets or capsules whole with a drink of water - they are specially made to release the medicine over a few hours into your body and should not be broken, crushed or chewed.
Some parts of the long-acting capsules do not get absorbed into the body and pass straight through. You might see small white balls or granules in your poo. This is not a problem.
What if I miss a dose?
If you remember later during the day, take it as soon as possible. However, if this is more than six hours after the dose should be taken, it is usually better to miss the dose and just start again at the next dose.
If you forget to take it by the next dose, just start again with the next dose.
Do not take a double dose.
What will happen if I forget to take my venlafaxine?
If you forget to take your tablets for a few days, you may start getting your old symptoms back, or get withdrawal symptoms (feeling dizzy or shaky, sleep problems (including difficulty sleeping and intense dreams), feeling irritable or anxious, feeling or being sick, and headaches). If this happens you should talk to your doctor about it.
Stopping the use of venlafaxine
Stopping this medicine quickly, or reducing the dose too much at once, may cause uncomfortable symptoms.
You can stop taking it safely by stepping down the dose gradually with your doctor’s help.
Once you start taking venlafaxine, the brain adjusts to having a new level of serotonin and noradrenaline around. If you stop taking venlafaxine suddenly, you could get some withdrawal symptoms.
Venlafaxine is not addictive, but you may get uncomfortable withdrawal symptoms if you stop taking it suddenly, as your body begins to miss it. It is better to agree stopping with a doctor who will reduce your dose gradually over about four weeks.
Some of the withdrawal symptoms you might get include:
- dizziness, feeling light-headed or having headaches
- tingling feelings like pins and needles or ‘electric shock’ feelings
- sleep disturbances (vivid dreams, nightmares, not being able to sleep)
- feeling anxious, nervous, agitated or confused
- feeling sick or being sick
- diarrhoea (loose poo)
- feeling tired and weak
- dry mouth and losing your appetite
- ringing in the ears
- feeling like you have got flu (muscle weakness and fever)
These symptoms should stop after one to two weeks for most people, but some people can get them for longer.
Most people get mild symptoms, but for some people they can be very intense.
Go and speak to your doctor if you have missed a few doses or have decided to stop taking your medication.
When you agree with your doctor to stop the venlafaxine, it is usually best to come off slowly over a few weeks. This will lower your risk of getting withdrawal symptoms.