Venlafaxine: uses, side effects and cautions

The NHS says venlafaxine is mainly used to treat depression, and sometimes anxiety, panic attacks and hot flushes in women who have had breast cancer. It is an SNRI. That means it increases both serotonin and noradrenaline, two chemicals that influence mood, which is how it differs from SSRIs that act on serotonin alone.

Venlafaxine is made as tablets and capsules. Slow-release products are taken once a day. Standard-release products are taken twice a day, morning and evening. Because the two are not interchangeable, check you have the type your prescriber intended, and ask the pharmacist if the packaging changes.

Swallow them whole with water and take them with food. A doctor will often start with a low dose and increase it after two or three weeks.

Keep the same product from the same supplier where you can, and tell the pharmacist if the tablets or capsules look different when you collect them. If you are unsure whether you have the slow-release or standard version, ask before you take it, since the number of daily doses depends on which one it is. Keeping a note of the time you take each dose helps when two doses a day are needed.

If you miss a dose, take it as soon as you remember unless the next one is near. In that case, skip it. Do not double up.

The NHS says that if you may have taken too much, you should call NHS 111 or, if you are very unwell, 999 for an ambulance.

Most side effects should ease after a couple of weeks as the body gets used to the medicine, according to the NHS. Speak to a pharmacist or doctor if they continue.

• Common: headaches, nausea, vomiting, dizziness, drowsiness, dry mouth, diarrhoea or constipation, sexual problems, insomnia and weight changes.

• Avoid driving or machinery if you feel dizzy or drowsy.

• Call NHS 111 for serotonin syndrome (fast heartbeat, sweating, muscle twitching, confusion), unexplained muscle pain or weakness, very low mood or thoughts of suicide. Anaphylaxis needs emergency help.

The NHS says venlafaxine may not suit you if you are allergic to venlafaxine or similar antidepressants. Diabetes, epilepsy, heart disease, glaucoma, bleeding disorders and a personal or family history of mania are all reasons to discuss it first.

The NHS names anticoagulants such as warfarin and apixaban, anti-inflammatory painkillers such as aspirin and ibuprofen, MAOIs and other antidepressants as medicines to check. Avoid St John's wort. Alcohol can increase the risk of side effects.

In pregnancy the NHS says it can be used at the lowest effective dose when needed. It may pass into breast milk, so speak to your doctor before breastfeeding.

Abrupt stopping may cause withdrawal symptoms. Your doctor will lower the dose gradually. If you have a side effect you are unsure about, you can report it through the MHRA Yellow Card scheme.