OTC Medicines and Drowsiness

There are some medicines that you can buy over-the-counter (OTC) from your pharmacy or a supermarket that have the potential to cause drowsiness. This includes medicines that you might take for:

• Cough
• Hayfever
• Worm treatments
• Analgesics
• Anti-nausea treatments
• Medicines for gastrointestinal upsets
  

Different substances affect people differently so something that might not cause you drowsiness could affect another person.

Predominantly it is antihistamines that can cause drowsiness. Among these there are two main types; the first generation that lead to most drowsiness and the second generation antihistamines that have less potential to cause sleepiness.

Other substances that have been reported to have the potential to cause drowsiness are opioids, used as analgesics, and hyoscine that is used for travel sickness.

First-generation antihistamines
This group of antihistamines, which have been in use for longer, is well known to have the potential to cause sleepiness.

Below is a list first generation antihistamines, known to cause sleepiness, which are ingredients in some OTC medicines such as allergy treatments, anti-nausea medicines, worm treatments, cough and decongestant treatments and analgesics.

• Brompheniramine
• Buclizine
• Chlorpheniramine
• Cinnarizine
• Clemastine
• Cyclizine
• Cyproheptadine
• Diphenhydramine
• Diphenylpyraline
• Doxylamine
• Meclozine
• Pheniramine
• Promethazine
• Triprolidine

Make sure you check with your pharmacist before taking any OTC medicine whether it could make you sleepy. If so you should not drive or operate machinery.

Second-generation antihistamines
This group of antihistamines is more recent – they were mainly developed as alternatives that would cause less drowsiness than first generation antihistamines.

Four antihistamines in this group are available to the public as ingredients in OTC medicines.

Some people will however still experience drowsiness when using this group of antihistamines so should still be aware that they could do so. You should therefore not drive or operate machinery when taking OTC medicines with these ingredients.

These antihistamines that are featured in some OTC medicines include:

• Acrivastine
• Cetirizine
• Loratadine
• Levocabastine (Only present in nasal spray or eye drop formats. Faint possibility of drowsiness if both used together, but nasal sprays and eye drops containing this ingredient should only be used together under medical supervision.)

Opiods
There are a number of opioids that are ingredients in OTC medicines, mainly analgesics and one antimotility treatment.

These are:

• Codeine
• Dihydrocodeine
• Loperamide
• Morphine

In low doses, opiods do not commonly cause drowsiness however you should still be aware of their potential to make you feel sleepy.

Muscarinic Antagonists
Muscarinic receptors can regulate gut motility. One muscarinic antagonist is available over-the-counter. This is hyoscine and it is featured in products for the treatment of motion sickness and in painkillers for stomach pain. It can cause drowsiness and you should not drive or operate machinery if you are taking a medicine featuring this ingredient.