Research carried out by the CA found that overseas pharmacists are unlikely to ask many questions about symptoms.
Of 54 chemists visited by researchers in Barcelona, Cairo and Istanbul, only one in four sold drugs which were entirely appropriate.
Some medicines sold for common complaints, such as upset stomachs, coughs and colds were potentially dangerous.
Diarrhoea treatment
In Egypt and Turkey, researchers were given antibiotics to treat diarrhoea that are only available on prescription in the UK.
Three Egyptian pharmacies provided Streptoquin, an antibiotic combination that is largely ineffective against diarrhoea, and which has been banned in many countries.
All the Spanish pharmacists correctly supplied the diarrhoea treatment loperamide - commonly known in the UK as Immodium.
However, none of the chemists visited emphasised the need to drink plenty of fluids, such as water or weak tea, or sold rehydration powders.
Chest infections
For simple chest infections most of the chemists sold innocuous cough mixtures, lozenges or decongestants.
However, several sold products that are potentially harmful to people with high blood pressure.
Two Turkish chemists prescribed penicillin antibiotics without inquiring about any history of allergy, and one Egyptian pharmacy sold a cough suppressant containing oxeladine, a substance banned in many countries over fears that it might cause cancer.
Patricia Yates, editor of Holiday Which? said: "If you are worried about getting the right drugs overseas, take a comprehensive first aid kit with medicines you might need for common complaints.
"Knowing the generic names for drugs will help you get the right treatment if you find it difficult to communicate your symptoms to the pharmacist."
The advice was echoed by the Royal Pharmaceutical Society of Great Britain.
A spokesman said: "Communication is the key. If the pharmacist does not speak good English, then go to another pharmacist who does - this should not be a problem in tourist areas.
"If you are being offered a local product ask if the pharmacist has a European or north American equivalent that has been through the proper testing procedure."