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Using Medicines Correctly

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:

  • Allergies such as hayfever
  • Cough
  • Anti-nausea treatments
  • Medicines for gastrointestinal upsets
It is vital that you read the instructions before taking any medicine; this includes the leaflet inside the box as well as the information on the outside of the packaging.

If you are taking medication that can cause drowsiness you should not drive or operate machinery.

If you have any queries or are unsure you should ask your pharmacist before taking any medicine.

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 include 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, cough and decongestant treatments.

  • 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.)

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.

Taking more than one OTC medicine at the same time can cause side effects and you should consult your pharmacist before doing so.

Sedative effects can be heightened by drinking alcohol so if you are on OTC medicines avoid alcohol – if you do drink be aware that you may experience increased drowsiness. is a directory of medicines and food supplements that are available 'over the counter' (OTC) from your pharmacist. The links below will take you to pages detailing products which may help treat or relieve the following symptoms:

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