When Danilo Di Luca got himself thrown off the Giro d'Italia a couple of weeks ago, it seemed like a gust of stale air blowing in from a half-forgotten past. Traces of erythropoietin had been found in a urine sample given by the 37-year-old Italian rider a few days before the start of the race. Di Luca had form, and plenty of it: his most recent ban had come after tests during the 2009 Giro – a race he had won two years previously – revealed the presence of Cera, a sophisticated form of EPO.

The cycling world was furious with him for reviving the spectre of its tainted history. But perhaps they should be less worried about veteran recidivists indulging in old doping habits than in the possibility of future scandals involving a new generation of drugs.

Over the past six months a number of riders have tested positive for GW1516, a synthetic substance which works on a muscle-building gene. It persuades the body to send more oxygen to the muscles by using up fat rather than carbohydrate or protein, which thus remain available to build muscle tissue. Athletes can employ it to train harder and increase their endurance, the classic job of a modern performance-enhancing drug.

It was first synthesised by GlaxoSmithKline, which saw the hugely lucrative potential for marketing it to people wanting to lose weight. But when the company's scientists tested it on rodents, they didn't like what they found. In large doses it induced cancers in various organs of the body, from the tongue and the thyroid to the testes and the ovaries by way of the kidneys and the liver. In 2006, without going any further, GSK dropped it. Yet this is the substance recently revealed to have been detected in samples taken during the Tour of Costa Rica last December from four local professionals – Paulo Vargas Barrantes, Pablo Mudarra Segura and Allan Morales Castillo, all of the BCR Pizza Hut team, and Steven Villalobos Azofeifa of the Coronado team – and from a Colombian rider Marlon Pérez, of the Colombia-Claro team.

Those results were announced in April, which also happened to be the month in which out-of-competition tests in Europe exposed the use of GW1516 by Valery Kaykov, a Russian rider with the RusVelo team, and Miguel Ubeto, a Venezuelan with Lampre-Merida.

Despite GSK's decision to end their efforts to clear the drug for medical use, others are manufacturing it without medical clearance. A single click reveals GW1516 to be the third highest-selling product on one internet site, at $119 for a 150-mg bottle.

On 21 March, shortly before the GW1516 positives were revealed, the World Anti-Doping Agency issued a warning against its use. "Clinical approval has not and will not be given for this substance," it said. "The side-effect … is so serious that Wada is taking the rare step of warning 'cheats' to ensure that there is complete awareness of the possible health risks to athletes who succumb to the temptation of using (it) for performance enhancement."

Clear enough. But GW1516 has a little friend. This one is called Aicar, pronounced "ay-car", and it does a similar job through different means. It is available on the same website, at $98 for 100mg, and the possible side-effects have yet to be publicised. But as Michael Stow, the head of science and medicine at UK Anti-Doping, told me : "We know that dangers exist, predominantly related to its effects on the heart and to levels of lactic and uric acid, which can result in conditions such as gout and arthritis."

Where GW1516 functions on a gene, Aicar sends its message through metabolic pathways, and there is evidence to suggest that some athletes combine the two in a cocktail that enhances the effects of both. And neither has been medically approved.

So is there a real cause for concern? "Yes," Andy Parkinson, UK Anti-Doping's chief executive, said. "We're concerned about athletes using any substances that haven't passed trials with the pharmaceutical companies, and the potential use of gene-doping has got to be a worry."

It is 18 months since Wada and the major pharmaceutical companies signed a joint memorandum of understanding, under which the industry supplies advance information about their new products to the anti-doping authorities, helping them to devise methods of recognising those falling outside the boundaries of acceptable use in sport.

"The pharma business is a highly competitive one and information on new drugs is commercially sensitive," Parkinson said, "so that was a big step forward." That co-operation led to a detectable "marker" being placed in Cera during the manufacturing process. None of that, however, can regulate what he calls illicit and copycat manufacturing. "We're seeing these things sold on the internet by people who have no regulator. The athletes who buy these products have no idea what they're receiving and putting into their bodies."

Given recent history, it is natural that cycling should come under the spotlight. "But other sports aren't immune," Parkinson said. Although he would not elaborate, it can be assumed that any endurance sport might contain athletes vulnerable to these new temptations.

As with previous generations of performance-enhancing drugs, the testers are running to catch up with the cheats. Once the use of EPO had been detected, it took several years to devise adequate tests for a substance that occurs naturally in the human body. GW1516, which is entirely artificial, can now be spotted with certainty. Identifying the exogenous use of naturally occurring Aicar involves the constant monitoring required by the bio-passport, where unusual fluctuations in the level of its presence within an individual athlete's body can be logged.

The threat posed to cheats by anti-doping measures is also reinforced by a significant improvement in retesting. "We've got bigger freezers," Parkinson said, "and there's a statute of limitations allowing us to keep them for retesting for up to eight years." A new substance that is hard to spot today might be easy to detect the day after tomorrow.

The cyclists so far found to have used these rogue products are not famous. They are not even the sort of riders to be found at the back of the Tour de France peloton later this month. They might not be the cleverest or more sophisticated users of doping products. Nor are they from a single team, or a single country, or even a single continent. Plenty of room for concern, then, that while the vast majority of cyclists battle to restore their sport's reputation, a delinquent minority is proving hard to budge.