This potentially dangerous ergolytic chemical is Guanidinopropionic Acid (GPA), which binds the creatine transporter and plugs it up so creatine can’t be transported into various tissues (similar to the concept of tamoxifen blocking the estrogen receptor, not allowing estrogen to bind). This is a problem, because most of our tissues can’t make creatine so it has to be transported in, and blocked transporters means a reduction in cellular creatine levels.
Bear in mind that creatine isn’t just a supplement, it’s a naturally occurring substance in our bodies that we need to survive! You know the impact of having 20% more creatine, now imagine having 80% less creatine! GPA induced creatine depletion can not only reduce muscle strength after a mere seven days of consumption (Gagnon et al., 2002), but has also been shown to convert fast-twitch muscle to slow-twitch (Ren et al., 1995)! So this substance might make you weaker and slower!
While these consequences should be enough to make you avoid supplements containing this chemical, there’s also a potentially dangerous side to consider: both our hearts and our brains have creatine transporters!!! Any time you start to mess around with our two most vital organs, it can’t be good. Fortunately, the brain seems to temporarily compensate for decreases in energy supply caused by GPA (O'Gorman et al., 1996), but do we really want our bodies to have to adapt to reduced energy levels? Of course not!
We also don’t want our hearts to be affected by GPA supplementation, but they are! In fact, 3 different studies showed that creatine levels in the heart dropped by 80-87% with GPA consumption in rats (Boehm et al., 2003, Neubauer et al., 1999; Horn et al., 2001). Now you can see why it’s nearly impossible to perform human studies using this substance! Clearly, you have to wonder what the manufacturers were thinking when they approved production of this supplement.
"But wait, there’s MORE! Order now and you’ll get another potentially dangerous ingredient for free!" One particular supplement ("SWOLE") combines GPA with another potentially dangerous substance known as Glycocyamine (G-amine). Sadly, G-amine (also known as guanidinoacetate) has been picked up by a few different supplement companies who obviously don’t do any research on what they’re getting people to ingest.
The reason G-amine is so popular (from a marketing standpoint, not from the consumers’) is because it is the precursor to creatine. Just like Testosterone can come from andro, creatine comes from G-amine. The theory is that you jack up G-amine levels and you get a whole bunch more creatine. The really asinine part is that, you can just directly take creatine!