Complex sentence: According to Alexander Shulgin in his book PiHKAL, MDPEA appears to be biologically inactive, likely on account of extensive first-pass metabolism by the enzyme monoamine oxidase.
Split into simpler sentences: According to Alexander Shulgin in his book PiHKAL, MDPEA appears to be biologically inactive. This is likely on account of extensive first-pass metabolism by the enzyme monoamine oxidase.