Tue Aug 1

Taking an antidepressant? Mixing it with other medicines – including some cold and flu treatments – can be dangerous

Written by Treasure McGuire, Assistant Director of Pharmacy, Mater Health SEQ in conjoint appointment as Associate Professor of Pharmacology, Bond University and as Associate Professor (Clinical), The University of Queensland

In the depths of winter we are more at risk of succumbing to viral respiratory infections ^[1] – from annoying sore throat, common cold and sinusitis, to the current resurgence of respiratory syncytial virus (RSV), influenza and COVID.

Symptoms of upper respiratory tract infection range in severity. They can include fever, chills, muscle or body aches, cough, sore throat, runny or stuffy nose, earache, headache, and fatigue. Most antibiotics target bacteria so are not effective ^[2] for viral infections. Many people seek relief with over-the-counter medicines.

While evidence varies, guidelines suggest medicines taken by mouth (such as cough syrups or cold and flu tablets) have a limited but potentially positive ^[3] short-term role for managing upper respiratory infection symptoms in adults and children older than 12. These include:

paracetamol or ibuprofen for pain or fever
decongestants such as phenylephrine or pseudoephedrine
expectorants and mucolytics to thin and clear mucus from upper airways
dry cough suppressants such as dextromethorphan
sedating or non-sedating antihistamines for runny noses or watery eyes.

But what if you have been prescribed an antidepressant? What do you need to know before going to the pharmacy for respiratory relief?

Avoiding harm

An audit of more than 5,000 cough-and-cold consumer enquiries to an Australian national medicine call centre found questions frequently related to drug-drug interactions (29%). An 18-month analysis showed 20% of calls concerned ^[4] potentially significant interactions, particularly with antidepressants.

Australia remains in the “top ten ^[5]” antidepressant users in the OECD ^[6]. More than 32 million ^[7] antidepressant prescriptions are dispensed on the Pharmaceutical Benefits Scheme each year.

Antidepressants are commonly prescribed to manage symptoms of anxiety or depression but are also used in chronic pain and incontinence. They are classified primarily by how they affect chemical messengers in the nervous system.

These classes are:

selective serotonin reuptake inhibitors (SSRI) such as fluoxetine, escitalopram, paroxetine and sertraline
serotonin and noradrenaline reuptake inhibitors (SNRI) such as desvenlafaxine, duloxetine and venlafaxine
tricyclic antidepressants (TCA) such as amitriptyline, doxepin and imipramine
monoamine oxidase inhibitors (MAOI) such as tranylcypromine
atypical medicines such as agomelatine, mianserin, mirtazapine, moclobemide, reboxetine and vortioxetine
complementary medicines including St John’s wort, S-adenosyl methionine (SAMe) and L-tryptophan

Medicines within the same class of antidepressants have similar actions and side-effect profiles. But the molecular differences of individual antidepressants mean they may have different interactions with medicines taken at the same time.

Types of drug interactions

Drug interactions can be:

pharmacokinetic – what the body does to a drug as it moves into, through and out of the body. When drugs are taken together, one may affect the absorption, distribution, metabolism or elimination of the other
pharmacodynamic – what a drug does to the body. When drugs are taken together, one may affect the action of the other. Two drugs that independently cause sedation, for example, may result in excessive drowsiness if taken together.

There are many potential interactions ^[9] between medications and antidepressants. These include interactions between over-the-counter medicines for upper respiratory symptoms and antidepressants, especially those taken orally.

Concentrations of nasal sprays or inhaled medicines are generally lower in the blood stream. That means they are less likely to interact with other medicines.

Woman holds glass of water and tissue to head.

Consult your pharmacist and only use treatments while symptoms persist. Shutterstock ^[10]

What to watch for

It’s important to get advice from a pharmacist before taking any medications on top of your antidepressant.

Two symptoms antidepressant users should monitor for shortly after commencing a cough or cold medicine are central nervous system effects (irritability, insomnia or drowsiness) and effects on blood pressure.

For example, taking a selective SSRI antidepressant and an oral decongestant (such as pseudoephedrine or phenylephrine) can cause irritability, insomnia and affect blood pressure.

Serotonin is a potent chemical compound produced naturally for brain and nerve function that can also constrict blood vessels. Medicines that affect serotonin are common and include most antidepressant classes, but also decongestants, dextromethorphan, St John’s wort, L-tryptophan, antimigraine agents, diet pills and amphetamines.

Combining drugs ^[11] such as antidepressants and decongestants that both elevate serotonin levels can cause irritability, headache, insomnia, diarrhoea and blood pressure effects – usually increased blood pressure. But some people experience orthostatic hypotension (low blood pressure on standing up) and dizziness.

For example, taking both a serotonin and SNRI antidepressant and dextromethorphan (a cough suppressant) can add up to high serotonin levels. This can also occur with a combination of the complementary medicine St John’s Wort and an oral decongestant.

Where serotonin levels are too high, severe symptoms ^[12] such as confusion, muscle rigidity, fever, seizures and even death have been reported. Such symptoms are rare but if you notice any of these you should stop taking the cold and flu medication straight away and seek medical attention.

Ways to avoid antidepressant drug interactions

There are a few things we can do to prevent potentially dangerous interactions between antidepressants and cold and flu treatments.

1. Better information

Firstly, there should be more targeted, consumer-friendly, online drug interaction information ^[14] available for antidepressant users.

2. Prevent the spread of viral infections as much as possible

Use the non-drug strategies that have worked well for COVID: regular hand washing, good personal hygiene, social distancing, and facemasks. Ensure adults and children are up to date with immunisations.

3. Avoid potential drug interactions with strategies to safely manage symptoms

Consult your pharmacist for strategies most appropriate for you and only use cold and flu medications while symptoms persist:

treat muscle aches, pain, or a raised temperature with analgesics such as paracetamol or ibuprofen
relieve congestion with a nasal spray decongestant
clear mucus from upper airways with expectorants or mucolytics
dry up a runny nose or watery eyes with a non-sedating antihistamine.

Avoid over-the-counter cough suppressants for an irritating dry cough. Use a simple alternative such as honey, steam inhalation with a few drops of eucalyptus oil or a non-medicated lozenge instead.

4. Ask whether your symptoms could be more than the common cold

Could it be influenza or COVID? Seek medical attention if you are concerned or your symptoms are not improving.