MEDICINES bought online or via mail order have been found to contain a banned substance that can increase the risk of heart attack or stroke.
Sibutramine is no longer allowed in any medicinal products within the EU because of health risks.
The Irish Medicines Board (IMB) said in a report that it was found among some of the 758,276 dosages of fake or illegal medicines that were confiscated last year by customs officers.
Some 153,042 of the units detained related to weight loss products, while 52,089 were supposed to treat male impotence.
Nearly 247,000 units confiscated were sedative products, and 16,848 contained anabolic steroids.
An IMB spokeswoman said other "undeclared" active substances found in other products included dimethocaine, a local anaesthetic with reported stimulant properties similar to cocaine, and thiosildenafil, which could lead to significant health risks.
The person who buys the products often believes they are a "natural" medicine, without knowing they contain active ingredients.
IMB chief executive Pat O'Mahony said: "As with previous years, the IMB is concerned with the consistent levels of counterfeit and illegal medicines being detained and is warning consumers of the dangers of purchasing medicines from unauthorised sources.
"The IMB strongly recommends that members of the public never purchase prescription medicines online as there are no guarantees as to the safety, quality or effectiveness of these products.
"Medicines purchased on the internet can pose serious health risks to those who use them. The supply of prescription-only medicines via the internet is illegal and no online pharmacy is authorised to operate in or into Ireland."
A total of 3,911 enforcement investigations involving breaches of medicinal product legislation were initiated. They included successful prosecutions of illegal suppliers of prescription medicines.
The figure includes the detention of prescription medicines being imported into Ireland via mail order for personal or commercial use.
The IMB gave the go-head for 77 clinical trials of new medicines, a 13pc increase over the previous year.
"Most of the trials were for the treatment of cancer (38pc) and haematology indications (21pc)," the report added.
The IMB received 2,757 (2,784 in 2011) reports of suspected individual adverse reaction to human medicines.
During 2012, 741 quality defects were reported to, or identified by, the IMB.
Two national recommendations were introduced that concerned children's medicines.
These were new dosage instructions for liquid paracetamol medicines for paediatric use, and advice that echinacea should not be given to children under 12 due to a lack of supporting scientific data.