Levels of toxins in fake tobacco - including tar, nicotine, carbon monoxide, lead, cadmium and arsenic - are all significantly higher than genuine brands.
As a result they pose an even greater threat to a smoker's health.
Counterfeit products have been found to contain as much as 30 times the lead levels of genuine tobacco.
A nationwide study, by a major cigarette company, into illicit tobacco trade found fakes - containing additional toxins - on sale for just £3 a packet.
Glasgow's illegal tobacco is joint cheapest in the country, alongside Edinburgh.
The Evening Times first told in November last year how Glasgow had been found to have the most readily available illegal tobacco in the UK.
Test purchases were carried out by trained buyers who identified locations where cartons, packs and pouches of counterfeit tobacco were on sale.
The study was conducted by former Scotland Yard Detective Chief Inspector Will O'Reilly, whose team bought illegal products at the Barras, in pubs and in an ethnic food shop.
He said: "While the cost of illicit cigarettes in Glasgow may seem low to the consumer, there are huge profits to be made by organised criminal groups.
"These cigarettes are manufactured for as little as 15 to 20p per packet.
"The gangs don't care who they sell to, target-ing the most deprived people in our society, as well as children.
"If plain packaging drives up the illicit market, as seen in Australia, even more money goes into the hands of organised crime.
"The government is already losing a substan-tial amount of tax money, so if the illicit market rises - as is anticipated with plain packaging - taxpayers lose out."
Cartons of cigarettes were bought in Glasgow for £40, while packs in North Lanarkshire and South Ayrshire cost £3.50, and £4 in Renfrewshire and Inverclyde.
During the study the team found thousands of packs and cartons of cigarettes, as well as roll-your-own pouches.
In Glasgow the product was found hidden in the meat section in an ethnic food shop.
As well as the Barras, the team found illegal copies of well-known cigarette brands in pubs, a social club and a mobile phone shop.
A Glasgow Trading Standards spokesman said: "Clearly, all tobacco products carry a substantial health risk, but there is evidence that counterfeit products can contain additional toxins."