Irish police have issued a warning about the use of counterfeit prescription drugs after two men died after an apparent accidental overdose.

The two men, one of his late 20s and the other in his early 30s, died in Tralee, County Kerry, last week and investigators believe that counterfeit tranquillizers purchased over the Internet may have caused their deaths.

Police found a quantity of what they believe is Zanax on the body of the 28-year-old, who was discovered in his home on Monday, June 6.

Three days later, a friend of the deceased died as a result of cardiac arrest. Police believe he had been using prescription sedatives.

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It is understood the men who died were heroin users who had been trying to come clean; one of the men had signed up for a drug treatment program, the Irish Examiner reports.

The double tragedy comes after the Irish Medicine Board (IMB) urged people to never buy medicines online.

Recent figures show that a record 822,484 medicinal products were seized at Irish airports last year, that represents a 66 percent increase from the previous year.

Tralee town, KerryGoogle Images