Awareness of your inner reality guides you to make an intelligent choice, and the body and mind concur. One must know the psychology of the vibrations of the body. Once you allow the chemicals in, you become a slave to them. They turn into desires and cravings. That is called alcoholism.
Drugs also take over the whole system.
There is a chemical influence in one's addiction to sex also. Even if the partner is full of negativities and a hindrance to one's growth, the person justifies the relationship because of the strong chemical influence. The person is not free from these physical and emotional bindings. The demand of chemicals is so strong that all spiritual ideas may go with the wind. That is why there is so much pain, suffering, and misery in the world.