Montelukast: uses, side effects and mental health cautions

Montelukast is mainly prescribed to prevent asthma symptoms, often where asthma is mild, and it can stop the condition worsening. It is also used for breathing difficulty brought on by exercise, for seasonal allergic symptoms such as sneezing, itchiness and a blocked or runny nose, and sometimes in people without asthma for hives that last for more than 6 weeks.

It is normally an add-on. Most people with asthma are given a steroid inhaler such as beclometasone or fluticasone first, and montelukast may be added if the prescriber thinks extra control is needed. Other options mentioned by the NHS include salmeterol, sodium cromoglicate and theophylline.

Leukotrienes are chemicals released during allergic reactions to things like dust and pollen and also during exercise. They tighten and inflame the airways. Montelukast blocks their action, so the airways are less likely to narrow. The NHS says the medicine starts to work immediately but takes about a day to help asthma symptoms, and that if it has had no effect after 4 to 8 weeks you should see your doctor about other options.

The NHS describes 10mg non-chewable tablets, chewable tablets in 5mg or 4mg strengths and 4mg granules in sachets. The usual dose is a 10mg tablet daily for adults and children aged 15 and over, a 5mg chewable tablet daily for ages 6 to 14, and 4mg daily from 6 months to 5 years, as granules or, over 2 years, a chewable tablet. Your prescriber's instructions always take priority.

Most people take it once a day in the evening, though some who get asthma from exercise are told to take it 2 hours beforehand. Never take more than one dose in a day. Swallow non-chewable tablets whole with or without food. Take chewable tablets at least 1 hour before food or 2 hours after. Granules can go straight on a child's tongue or into a spoonful of cold soft food such as yoghurt, taken within 15 minutes, but must not be dissolved in a drink.

If a dose is missed, skip it and take the next one the following day at the usual time. Medicine taken for asthma should continue even when there are no symptoms, and it only works while being taken.

More than 1 in 100 people get diarrhoea, a high temperature, headaches (which usually go within the first week), stomach pain, nausea or vomiting, or a mild rash. Drink fluids if you have diarrhoea or vomiting, and note that severe diarrhoea or vomiting can reduce the protection from the contraceptive pill.

The NHS lists signs that call for a doctor or 111 straight away: anxiety, depression or aggression; hallucinations; harder concentration or memory; new or worse sleep problems such as nightmares or sleepwalking; speech changes or stuttering; shaking; an unusual or fast heartbeat; a flu-like illness with pins and needles or numbness, worsening asthma or a rash; and yellowing of the whites of the eyes or skin, a possible sign of liver problems. Thoughts of harming yourself need 999 or A&E. It also suggests telling family or friends you are taking it so they can notice changes in mood, sleep or behaviour.

Swelling of the lips, mouth, throat or tongue is a possible allergic emergency. Suspected side effects can be reported through the Yellow Card scheme.

Most adults and children from 6 months can take montelukast. Tell your doctor if you have ever had an allergic reaction to it, or have a rare inherited problem with galactose, including Lapp lactase deficiency and glucose-galactose malabsorption, because some forms contain a sugar.

The NHS names some medicines that may alter how it works: the epilepsy medicines phenobarbital and phenytoin, rifampicin, and gemfibrozil. Everyday painkillers are usually safe, but avoid aspirin or ibuprofen if they have ever made your asthma worse.

You can take montelukast in pregnancy and it is important to keep asthma controlled; tell your doctor if you become pregnant, as they may review the treatment. If a doctor, health visitor or midwife says your baby is healthy, you can take it while breastfeeding, since tiny amounts pass into milk. Raise concerns if the baby feeds poorly, seems unusually sleepy or irritable, or has diarrhoea. There is no evidence of an effect on fertility.

Montelukast does not usually affect driving or cycling, but avoid both if you hallucinate, shake, or cannot concentrate or make decisions. Alcohol and food are not restricted.

Do not stop without speaking to your doctor, because symptoms may worsen. It is not known to cause problems if used long term. If you or your child develop troublesome mood, sleep or behaviour effects, your prescriber can discuss other preventer options such as a different inhaler or an antihistamine for allergic rhinitis.