Like all medicines, venlafaxine can cause side effects in some people, but many people have no side effects, or only minor ones.
Some of the common side effects of venlafaxine will gradually improve as your body gets used to it.
Common side effects
These common side effects of venlafaxine happen in more than 1 in 100 people. There are things you can do to help cope with them:
Feeling sick (nausea)
Stick to simple meals and do not eat rich or spicy food. If it carries on, tell your doctor.
Sweating and hot flushes
Try wearing loose clothing and using or a fan, where possible. If there is no improvement after a week, speak to your doctor.
Headaches
Make sure you rest, and drink plenty of fluids. It’s also best to avoid drinking too much alcohol. Ask your pharmacist to recommend a painkiller.
Headaches usually go away after the first week of taking venlafaxine. Talk to your doctor if they last longer than a week or are severe.
A dry mouth
Chew sugar-free gum or sugar-free sweets.
Feeling dizzy
If venlafaxine makes you feel dizzy when you stand up, try getting up very slowly or stay sitting down until you feel better. If you begin to feel dizzy, lie down so that you do not faint, then sit until you feel better.
Do not drive, ride a bike or use tools or machinery if you feel dizzy.
Feeling sleepy
Do not drive, ride a bike or use tools or machinery if you're feeling sleepy. Cut down the amount of alcohol you drink as this will make you feel more tired. If this symptom does not go away after a week or two, ask your doctor for advice.
Being unable to sleep (insomnia)
Take venlafaxine first thing in the morning.
Constipation
Get more fibre into your diet such as fresh fruit and vegetables and cereals, and drink plenty of water. Try to exercise, for example, by going for a daily walk or run. If this does not help, talk to your pharmacist or doctor.
If this advice does not help and any of these side effects bother you, talk to your doctor or pharmacist.
Serious side effects
It's not common, but some people (less than 1 in 100) may have serious side effects when taking venlafaxine.
Book an appointment with your doctor if:
- you gain weight or lose weight without trying
- you have changes in your periods such as heavy bleeding, spotting, or bleeding between periods
Call your doctor or call 111 now if:
- you get constant headaches, long-lasting confusion, weakness, or frequent muscle cramps – these can all be signs of low sodium levels in your blood
- you have feelings of overwhelming happiness (euphoria), excessive enthusiasm or excitement, or a feeling of restlessness that means you cannot sit or stand still
- you have unexplained muscle pain or weakness
- the whites of your eyes or skin turn yellow, although this may be less obvious on black or brown skin – this can be a sign of liver problems
- you have any changes in your eyesight, like blurred vision or dilated pupils
- you cough up blood or have blood in your pee
- you have black or red poo, or blood in your vomit – these can be signs of bleeding in the stomach
- you are bleeding from the gums, or have bruises that appear without a reason or that get bigger
- you get shortness of breath, or a fast or irregular heart beat
- you have thoughts about harming yourself or ending your life
Immediate action required: Call 999 now if:
- you get chest pain or pressure in your chest, shortness of breath, or a fast or irregular heart beat
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to venlafaxine.
Immediate action required: Call 999 now if:
- your lips, mouth, throat or tongue suddenly become swollen
- you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
- your throat feels tight or you're struggling to swallow
- your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
- you suddenly become very confused, drowsy or dizzy
- someone faints and cannot be woken up
- a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)
You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.
These can be signs of a serious allergic reaction and may need immediate treatment in hospital.
Long-term side effects
For most people, venlafaxine is safe to take for a long time and there are no lasting effects.
A few people may get sexual side effects, such as problems getting an erection or a lower sex drive. In some cases these can continue even after stopping the medicine. Speak to your doctor if you are worried.
Other side effects
These are not all the side effects of venlafaxine. For a full list, see the leaflet inside your medicine packet.
You can report any suspected side effect using the Yellow Card safety scheme.