Exendin-4 is the natural form found in the gila monster. Because of the obvious difficulty in smoking a gila monster (they are impossible to keep lit, just ask Tom Isaacs
![Big Grin](images/smilies/biggrin.gif)
)as well as problems with enzyme degradation, the other forms are synthetic mimics but not exact duplicates.
The original research touted the anti-PD effects of stimulating GLP-1 receptors in the brain. When it was found that Ex-4 could do so (and lead to a patentable product) things zeroed in on it.