OTC medicines and drowsiness

Some over-the-counter (OTC) medicines have the potential to make people feel sleepy. This can have a beneficial effect, such as helping someone sleep if they are suffering from a cough, but in other circumstances can pose a risk, particularly on people’s ability to drive safely.

Which medicines can cause drowsiness?
These include medicines that might be taken for:

  • Allergy relief e.g. Hayfever
  • Cough
  • To prevent nausea e.g. travel sickness
  • Sleep remedies

Predominantly it is antihistamines that can cause drowsiness. Among these there are two main types; the first generation (sedating antihistamines) and the second generation antihistamines (non-sedating antihistamines) that have less potential to cause drowsiness.  The first generation sedating antihistamines can only be bought in pharmacies and are behind the counter so a pharmacist or trained assistant can give advice when they sell them.

Individuals have different sensitivity to particular ingredients known to cause drowsiness, so a product that causes drowsiness in one person may have no effect on someone else.  There is increasing understanding that there is a genetic link and that some people metabolise such ingredients differently. Factors such as taking more than one OTC medicine at the same time and drinking alcohol can also increase the risk of drowsiness. 

Many of the products containing sedating antihistamines and well known to cause drowsiness (e.g. diphenhydramine) are only recommended for night time use as they help people to sleep. 

It is important to note that illness itself can be a distraction for drivers if the symptoms are not treated.  Consumers should ask their pharmacist for advice on choosing a suitable product. 

Drowsiness warnings
Medicines labelling is regulated and approved by the Medicines and Healthcare Products Regulatory Agency (MHRA).

Products that have the potential to cause drowsiness have to display a warning statement on the back of the pack.  This reads:

"This medicine can make you feel sleepy. Do not drive while taking this medicine until you know how it makes you feel. See the leaflet inside for more information."

The warning on packs and information in patient information leaflets (PILs) was reviewed and updated to reflect the new drug driving law:

Drug Driving Law
From March 2015, it will be illegal to drive if you’re unfit to do so because you’re on legal or illegal drugs. Legal drugs are prescription or over-the-counter medicines. If you’re taking them and not sure if you should drive, talk to your doctor, pharmacist or healthcare professional.

Further details can be found on the GOV.UK website