An undercover investigation has shown how people can easily source drugs online - and buy the illicit substances less than a day later in central Dublin.

As part of our investigation series 'At Risk - Teenagers and Drugs', we sought to obtain illegal drugs through social media, and were presented with an opportunity to purchase them on O'Connell Street.

Drugs including cannabis, ecstasy, cocaine and so-called party pills are all openly being marketed to Irish users on social media websites.

Security sources have claimed that dealers are increasingly taking advantage of social media and other websites to sell their products and avoid detection by gardaí.

But despite the warnings issued by gardaí and the HSE about buying drugs over the internet, our undercover reporter discovered that the business is still booming online.

After logging on to a Facebook page that discussed drug use in Ireland, we asked a number of users where drugs could be bought in the city centre.

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We received a range of different advice. However, one Facebook user directed us to an advert on a popular website.

The website was openly offering "pollen" for sale. Pollen is one of the strongest and most expensive types of cannabis resin available in Dublin.

It read: "Lovely fresh pollen available city centre €50 a q. 100% genuine and face to face meet, no bulls**t no timewasters please."

After a quick exchange of emails, the dealer - who used the name Colm - sent our reporter his mobile number and offered to meet the next day to sell us an ounce of cannabis (28g) for €180.

Despite the fact that it is one of the most heavily policed parts of the city, the dealer arranged to meet us at the GPO on O'Connell Street.

After exchanging phone numbers, he asked our reporter if he was an undercover Garda - which he denied.

Bizarrely, when we arrived at the meeting point a Garda van was parked just metres away in the centre of O'Connell Street.

But when we phoned the dealer, he was undeterred.

He said: "Just walk towards the statue."

When quizzed if he meant the statue of Labour and 1916 hero Jim Larkin, he replied, "Yeah, with the arms."

After meeting and shaking hands in the shadow of the Garda van, Colm asked our reporter: "Where do you want to walk?"

He then pointed towards the road behind Clerys department store, saying: "We can walk down the lane over there."

As they walked, Colm said he had been selling cannabis to make extra money.

After viewing the cannabis, our reporter told the dealer that he was going to get the cash from the bank machine and would meet him outside a coffee shop in a few minutes.

We never completed the purchase.

Cannabis is not the only drug being sold online to Irish users.

One dealer - who uses the moniker Charlie Sheen - emails out a weekly product and price list to his customers.

Last month, his product list read: "added to stock 3mmc and weed cheese strain …out of stock mdma, ket, upjohn … coming soon flake weed cheese strain coke, ket, d10, upjohn90, diclazepam."

A recent report by the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) said that online drug dealing - in particular in synthetic ecstasy and cocaine - was the continent's biggest narcotics growth market.

In 2013, the EMCDDA identified some 650 websites selling these substances to the European market, which, they believe, "represents a new challenge for law enforcement."

Drugs are still being openly sold on another popular website, which also hosts a series of 'adult ads'.

In one recent post, a dealer was offering to sell prescription-only drugs straight from the packet.

His ad - entitled 'Vals and Zimmos available' - claims he has benzodiazepines for sale.

He claims: "They're both sleeping pills but the temazepam '30mg' seems to be stronger, i.e. they'll keep u asleep for a little longer and there's less chance of waking during the nite.

"I have the 30mgs here in blister trays as well as Xanax and valium."

Our investigation - which is carried in the Irish Independent 'Review' section today - also shows how head shops, which were banned in Ireland in 2010, have now gone online.

Designer drugs such as N-bombs are increasingly popular among Irish teenagers, along with cannabis, ketamine, ecstasy and GHB.

Gardaí also say that they are seriously concerned at a noticeable upsurge over the past year in the demand for ketamine, a tranquilliser that is used in veterinary medicine.

Another dangerous drug to appear on the Irish club scene is gamma-hydroxybutyrate, or GHB, which is a solvent found in nail-varnish remover and industrial cleaning agents.

GHB - which is a diluted form of Rohypnol - comes in liquid form, and users put drops of the solution into their drinks in order to experience an immense psychoactive rush.

"We cannot overemphasise the risk of overdose and even death from using this drug, it is potentially lethal," one Garda expert stressed.

Irish Independent