Matter Over Mind

It was recently reported that a drug for the Parkinson's Syndrome, produced in it's users an obsession for gambling. Can something that was ingested produce such a purely mental reaction. But gambling is evil is it not? Considering evil a loss of perspective and consequence. Can a good man be corrupted by a couple of tablets? My friend here, mocks my naivete. The herblore and common knowledge of a thousand independent cultures abound with instances of substances that produce in their users effects ranging from the mystical to the malefic. You never heard of anti-depressants, my friend? Riddle me this, if what you ingest can influence your behavior, attitude and mood then what does the spread of McDonalds and it's ilk around the world suggest?