By now you would have heard about GW1516, a banned substance that five riders have tested positive to in the past week. And you might have heard of AICAR, a similarly restricted compound that can be used to boost performance. But how do they work? How safe are they? And how widespread is their use in the pro peloton?

Late last week Russian cyclist Valery Kakov was suspended by his RusVelo team after an out-of-competition test was found to contain traces of the banned, black market substance known as GW1516. And just this week it’s come to light that four Costa Rican riders — three from the same team — have also tested positive for GW1516 and been provisionally suspended by the UCI.

Cyclists being caught using banned substances isn’t groundbreaking news — particularly in light of the Armstrong saga — but the case of Valery Kakov and the four individuals in the Costa Rican case is a little different. Unlike EPO, for example, GW1516 hasn’t been approved for clinical use anywhere in the world.

The compound was first investigated by GlaxoSmithKline (GSK) who were looking to develop an “exercise in a pill” to help combat the worsening obesity epidemic. The drug passed pre-clinical studies and was allowed to be tested in humans for Phase I, II and IV trials.

The trials delivered some success (see more below) but when high-doses of the drug were linked with increased rates of cancer in animals, GSK decided to scrap further development of the drug for humans. To quote a GSK representative, “toxicities were found in routine, long-term animal studies that were being conducted in parallel with the clinical studies.”

Or, to quote an article in New Scientist “tests on rats showed that at all doses, the drug rapidly causes cancers in a multitude of organs, including the liver, bladder, stomach, skin, thyroid, tongue, testes, ovaries and womb.”

We’ve all heard the horror stories about the negative side-effects of EPO-use — including athletes whose blood got so thick with red blood cells that their heart simply couldn’t pump it — but it would seem taking GW1516 is even riskier (although this is only based on studies in rodents).

Indeed, the World Anti Doping Agency took the highly unusual step late last month of issuing a warning about the potential dangers of GW1516, which is also known as GW501516 and marketed as Endurobol:

The side effect of this chemical compound 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 GW501516 for performance enhancement.

While it’s not clear where Kakov got the GW1516 from — and, to be fair, he’s still entitled to a B sample before we’ll know conclusively whether he has used the compound — it certainly is available. GW1516 is freely available as a supplement or “research reagent” and is made legally by research laboratories for scientists.

Indeed, a quick internet search reveals a handful of online retailers that claim to be selling the product, mainly, it would seem, to the bodybuilding market. And skimming through various bodybuilding forums reveals an enthusiasm among some to try the product, either in spite of or in ignorance of the dangers.

So why would Kakov be taking GW1516? Well, again, we need to give him the benefit of the doubt (and a chance to have his B sample tested), but it seems GW1516 can have a marked effect on an athlete’s ability to build endurance and lose weight by utilising body fat for energy.

In a series of experiments in the 2000s, Ronald M. Evans from the Howard Hughes Medical Centre and Salk Institute showed that mice who were given GW1516 were able to run for twice the distance of their non-dosed counterparts — a huge boost in endurance. How is this possible?

To quote a BBC article, GW1516 appears to “have an effect on a gene that’s involved in the building and regulation of muscle” — a gene known as PPAR-delta. The research done by Evans and his colleagues showed that giving GW1516 to the mice enhanced the activity of the PPAR-delta gene, leading to the development of slow-twitch muscle that will preferentially burn fat over sugar or muscle protein.

You can see the benefit for endurance athletes here: if exercise is burning fat rather than carbohydrates and muscle protein, then you can utilise more energy sources without losing muscle mass.

Not only that, but when GW1516 is combined with another “fitness in a pill” compound, AICAR, it can create endurance benefits far greater than either compound in isolation.

AICAR activates so-called AMP-activated protein kinase (AMPK) which stimulates glucose uptake by skeletal muscle cells. The mice that were given AICAR by Evans and his team were able to run 44% further than the mice that didn’t get the drug. Most startling of all, the mice saw that 44% benefit without doing any training.

It’s for this reason that AICAR (and GW1516 as well) was heralded as “exercise in a pill” and the reason that it has potential as a performance-enhancing drug.

This is an excellent video from French TV (with English subtitles) that investigates the use of AICAR/GW1516 in cycling.

It’s worth noting that AICAR has been used in clinical trials since the 1980s, to quote Outside Online, “for the treatment of ischemic reperfusion, a rare complication of coronary bypass surgery that occurs when blood flow restored to previously damaged arteries causes inflammation and damage to heart tissue.”

By contrast, only limited human testing has been done on GW1516 and, as mentioned earlier, it hasn’t been approved for clinical use anywhere in the world.

But one of the things AICAR and GW1516 have in common is that they’re both on WADA’s banned substances list (GW1516 as a PPAR-delta “agonist” and AICAR as a PPAR-delta AMPK axis agonist). Which raises the question: where is drug testing up to when it comes to AICAR and GW1516?

We’re all familiar with the fact that cyclists who took EPO were able to beat the system for many years because the drug testing regime wasn’t up to date. Could this be the case with AICAR and GW1516? Or are the recent positive tests just a sign that these substances have been used in the pro peloton for many years and that drug testers are only now starting to catch up?

For a start, it’s important to realise that cycling authorities have known about the performance-enhancing potential of AICAR and GW1516 for several years now. When Ronald M. Evans published his research about GW1516 in the journal Cell in 2007, the BBC the New York Times ran stories about research, heralding the discovery as a breakthrough in the fight against obesity.

And importantly, Evans tipped off WADA before he published his Cell paper and was later asked to develop tests for both GW1516 and AICAR. As Joe Lindsay wrote in the Boulder Report last week:

Anti-doping authorities [now] have a test for GW1516, which is relatively easy to find in urine with existing testing procedures, as it’s not a naturally occurring substance in the body. What’s more, clinical research shows that the drug is detectable as long as 40 days after a single dose.

AICAR, by contrast, is considerably harder to test for. Unlike GW1516, AICAR is naturally produced in the body, making it more difficult to detect any of the artificial form of the substance that might have been added.

But, as The Inner Ring reported, the WADA Accredited Cologne laboratory — the lab that detected GW1516 in Kaykov’s sample — “has now perfected an AICAR test”. Not only that but research published in 2010 has established the baseline values for naturally occuring AICAR in elite athletes.

So, in theory, if a cyclist has been taking AICAR, and their samples have been tested in one of the very few advanced laboratories that have the right equipment, they should get caught. But, as yet, no cyclist has ever tested positive for AICAR use (although a former team doctor was arrested with AICAR in his luggage).

And there are some drawbacks to AICAR use. For a start, it’s very expensive — somewhere in the vicinity of half a million euro for a treatment in a lab in Vienna, according to French paper Libération. There’s also a suggestion that athletes using AICAR would see a significant increase in lactic acid creation. And finally, only limited testing has been done on humans when it comes to AICAR so there might be further complications we don’t even know about yet.

Of course, none of this is to say that AICAR isn’t being used. You might recall the 2009 study that showed some athletes would willingly take a substance that ensured both success in their chosen field and an early death. There’s no reason to suspect this isn’t the case here as well.

In fact, if you believe some reports, AICAR has been used in the pro peloton for a number of years. In 2009, the French Anti-Doping Agency famously announced that they suspected AICAR had been used in that year’s Tour de France, while declining to name specific individuals.

We’ve spoken with a few of our trusted sources within the pro peloton and they confirmed that they’d heard of GW1516 and AICAR, but that they didn’t know much else. It doesn’t appear that these drugs are spoken about much in the bunch, but then neither was EPO until you were on the “inside”, as we’ve all learned from the Lance Armstrong saga.

We’ve also been told that riders within the pro peloton have their own suspicions and doubts when they see spectacular performances along with substantial decreases in body fat. Our sources suggest it’s unlikely that the use of GW1516 and AICAR is widespread, but with WADA testing for these substances, we’ll soon find out when good riders start gaining weight and not performing anymore.

We’ve also spoken with others with connections to pro cycling and while there’s definitely anecdotal suggestions of AICAR/GW1516 use, no-one’s willing to go on the record to say as much.

So, like everybody else, we’ll just have to wait and see if AICAR/GW1516 turn out to be “the new EPO” as some people have suggested, or if, as Herman Ram of the Dutch Anti-Doping Authority told VeloNation “AICAR is a bit of a hype (sic)”.

Either way we can only hope that the positive tests for GW1516 don’t continue and that the positive tests for AICAR don’t start. And then we need to hope that a lack of positive tests means a lack of doping.

CyclingTips would like to thank Dr Benjamin Koh, Dr Nicole van Bergen and James Heathers for their assistance in putting this article together and ensuring its accuracy.

Click here to read more about blood doping and click here to read more about gene doping.