OTC medicines and drowsiness

Some over-the-counter (OTC) medicines have the potential to cause drowsiness. 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
Antihistamine products are required by law to carry a warning statement on the label. This reads:
Warning: may cause drowsiness. If affected do not drive or operate machinery. Avoid alcoholic drinks.

This warning has been on products for many years and is a statutory warning which means it legally has to be displayed on medicine packs that contain sedating antihistamines.

Research with consumers has found that the warning could be clearer.¹For example, "this medicine may make you sleepy" is easier to understand than “may cause drowsiness”. However, manufacturers are unable to change the wording on packs unless the legislation is changed.

The Medicines and Healthcare products Regulatory Agency (MHRA) has started to review the UK medicines legislation and the drowsiness warnings are part of the legislation scheduled to be reviewed and potentially improved.

Traffic light labelling
In France, a ‘traffic light’ system with pictograms is used to warn about drowsiness and it was suggested in the North Review, an independent report on drink and drug driving in Great Britain commissioned in December 2009, that a similar system should be adopted in the UK.²

In response to the North Review, the government expressed concern that there is a lack of robust evidence about the effectiveness of pictograms in communicating information and that warning symbols were open to misinterpretation.

It stressed that if warning symbols were to be introduced, the meaning of any such symbol would need to be clear; and patients, the public, and healthcare professionals would need to be able to take appropriate action. This would require a process of user testing.³

The government added that MHRA has been working to secure agreement within Europe to develop a single, simple labelling system for medicines, based on the risk of impairment to a patients' ability to drive. The labelling system will then form the basis for clear and consistent information to be given to patients in the UK and across Europe.

¹ BBC News website: Medicine lables to be made clearer

² North Review of Drink and Drug Driving Law

³ Government's response to the North Review