GMOs are problematic for a number of reasons, some of which we are only beginning to verify now that they are more common in the market.
Gnosis is a path of purity. Our physiology and psychology is an alchemical laboratory that synthesizes everything we consume into sexual energy, which is essential to our spiritual work. The better quality our sexual energy, the more we can accomplish through initiation. Therefore, any amount of GMOs presents issues in levels we are not even conscious of.
Regarding smoking and drinking:
If you want success with these studies, you must neither drink alcohol, nor smoke, nor eat too much red meat. Do not worry; cultivate the habit of being happy. -Samael Aun Weor, Aztec Christic Magic
Yes, as with everything in life, what you do is a personal choice. However, we do not recommend ingesting intoxicants, drugs, alcohol, chemicals, or harmful substances, because a polluted temple is not conducive to this esoteric path. When you ingest these substances, you corrupt your sexual energy. Therefore, we don't advise it.