Genuine :

Unnatural : not existing in nature, artificial, abnormal.
Synthetic : made by chemical synthesis, especially to imitate a natural product.
Artificial : made or produced by human beings rather than occurring naturally, especially as a copy of something natural.
Sham : a thing that is not what it is purported to be, splash, pretense, veneer.
Genuine : truly what something is said to be, authentic.

Antonym of Genuine is Sham.