Sales of codeine-containing products such as Nurofen Plus and Solpadeine fell by almost half during August, after new guidelines for pharmacists governing their use came into effect at the beginning of the month.

Latest industry figures supplied to GlaxoSmithKline Ireland, manufacturer of a range of over-the-counter medicines including Solpadeine, show the overall number of packets of such products sold through pharmacies fell by 45% last month when compared to August 2009.

Under the new Pharmaceutical Society of Ireland guidelines on the sale and display of the products – which came into effect on 1 August – pharmacists have to ensure customers know how to use such medicines properly.

As a result, codeine medicines such as painkillers and cough bottles must only be supplied under the personal supervision of a pharmacist, who must advise customers that they only be used when considered necessary and for the shortest time possible.

This has prompted resentment among some people at being subjected to what they claim is a type of " interrogation" when they look to purchase these over-the-counter drugs.

However, supporters of the guidelines point to the fact that products containing codeine can be habit-forming and the new rules will help to ensure they are only being taken by those who really need them.

Niall O'Shea, head of regulatory and external affairs with GSK in Ireland, said he believed there was a need for pharmacists to be allowed more discretion when it comes to selling products containing codeine.

"I think it is a big drop in sales, more than I would have expected, to be honest," he told the Sunday Tribune.

"The guidelines are very detailed, and it may be that pharmacists feel compelled to go into a very high level of detail in interpreting them… maybe they feel they have to follow them to the letter of the law."

He suggested that some patients who in the past had access to codeine-based products as one of a range of pain relief options may now be shying away from having to answer the questions posed by their pharmacist.

"So then they go to their doctor, which they have to pay for," he said. "The majority of people taking codeine products use them properly. The drop in sales would not be in any way comparable to the number of people who may have had a problem with codeine use."