Medication-induced depression: when a medicine affects your mood

Depression is described by the NHS as more than simply feeling unhappy or fed up for a few days; it is persistent sadness for weeks or months and is a real illness with real symptoms. Medication-induced depression is the term used when a medicine, or the way a medicine is used, is thought to have caused or contributed to those symptoms.

This is a recognised but uncommon route to depression. NICE CKS list other drug adverse effects as an uncommon cause of depressive symptoms when setting out what else depression might be. It sits alongside other things that can look like or contribute to depression, such as bereavement, anxiety disorders, bipolar disorder, substance misuse, neurological conditions and medical conditions such as anaemia or an underactive thyroid.

It can be hard to tell cause from coincidence. People are often prescribed medicines for conditions that themselves affect mood, such as chronic pain or other long-term illness, which NICE CKS list among risk factors for depression. That is why timing, dose changes and the full medicine history are examined carefully.

NICE CKS name the following when listing drug adverse effects as an uncommon cause of depressive symptoms. Being named does not mean the medicine commonly causes depression, and most people who take these medicines do not develop it.

The MHRA Drug Safety Update on montelukast reminds healthcare professionals to be alert for neuropsychiatric reactions, which have been reported in adults, adolescents and children. It says adverse reactions affecting sleep, behaviour and mood have been infrequently reported, and lists sleep disturbances, depression and agitation as possibly affecting up to 1 in 100 people taking it, disturbances of attention or memory in up to 1 in 1,000, and very rarely hallucinations and suicidal behaviour in up to 1 in 10,000.

Its advice to patients and carers is to read the leaflet, not to stop montelukast without talking to a doctor or asthma nurse first, and to seek medical advice if reactions occur so the benefits and risks of continuing can be weighed. The same principle applies to any medicine: report the change, do not simply stop.

The symptoms are those of depression generally. The NHS lists psychological symptoms such as continuous low mood, feeling hopeless and helpless, tearfulness, guilt, irritability, loss of motivation or enjoyment and thoughts of self-harm, physical symptoms such as slowed movement or speech, changes in appetite or weight, aches and pains, low energy, low sex drive and disturbed sleep, and social symptoms such as withdrawing from friends and hobbies.

The NHS says to see a GP if you have symptoms of depression for most of the day, every day, for more than 2 weeks, and particularly if symptoms are not improving, your mood affects work or relationships, or you have thoughts of suicide or self-harm. If you have thoughts of harming yourself or ending your life, or feel you cannot keep yourself safe, this is an emergency: call 999 or go to A&E, or call NHS 111 for urgent mental health advice.

Tell the GP or pharmacist when the low mood began in relation to any new medicine or dose change, and bring a list of everything you take including over-the-counter products and supplements.

The NHS says there are no physical tests for depression, but a GP may carry out urine or blood tests to rule out conditions with similar symptoms, such as an underactive thyroid, and the main way of making the diagnosis is by asking about general health, how you are feeling and how it affects daily life, medical history, previous mental health problems, lifestyle and recent triggers.

NICE CKS add that assessment includes onset, duration, pattern and severity of symptoms, coexisting conditions, risk factors including family history, suicidal ideas and current and previous medication. In suspected medication-induced depression, the prescriber considers whether the timing fits, whether the medicine is still needed, and whether an alternative is available.

Management depends on how severe the symptoms are and on how important the medicine is. NHS and NICE sources do not give a single recipe, and the options a prescriber may consider include reviewing whether the medicine is still needed, changing the dose or switching to an alternative. For montelukast, the MHRA advises careful evaluation of the risks and benefits of continuing if neuropsychiatric reactions occur. Some medicines should not be stopped suddenly, which is why the decision must be made with the prescriber.

Treating the depression itself follows the usual pathway. The NHS says treatment usually involves a combination of self-help, talking therapies and medicines, with watchful waiting, guided self-help, exercise and talking therapies for mild depression and antidepressants plus talking therapy for moderate or severe. You can refer yourself to NHS talking therapies without seeing a GP. If antidepressants are started the NHS says to contact a GP straight away if feelings of hopelessness or suicidal thoughts start or get worse.

When a medicine is clearly responsible and can be safely changed, mood often improves, though the sources used here do not give figures. The NHS says that with the right treatment and support most people with depression can make a full recovery. It also says that it is best not to delay seeking help, because the sooner you see a doctor, the sooner you can be on the way to recovery.