Free will is not totally free if physical / chemical agents can alter its outcome. This is why antidepressants come with a suicide risk warning.
...if all actions are predetermined then you cannot act as if you have choices. Acting is a volitional process of the very type you are denying. In your model there is no acting, there is only a differential equation of the universe cranking out its next time step.He is so close! He admits that in his world-view everything is predetermined, but in the next breath he obfuscates that unsavory factoid by claiming that he can “act” as though he has free choices. He can freely chose, he believes, to pretend that he can freely choose.
-Nuclear physicist Dave Heddle