I am a geriatrician (old person doctor) so Parkinson's Disease is one of my specialties. Interesting article.
Parkinson's Disease is a disease that essentially results from a deficiency of dopamine in the brain (either through a lack of dopamine itself or decreased dopamine receptors). Medications obviously target these receptors.
The psychotic side effects of all medications that effect dopamine are well known. I'm not going to pretend to understand the biochemical mechanisms surrounding this, it is very complicated and still incompletely understood. I can however point out that dopamine overactivity is a recognized pathological mechanism in schizophrenia, and that the well known side effects of all antipsychotic medication include a Parkinsonian like syndrome which causes stiffness etc.
Back to Parkinson's and its medications. As i said earlier, psychotic side effects are very common. In Parkinson's, the psychosis has a certain flavour to it based on another side effect. This side effect is called tardive dyskinesia or stereotopy, where patients develop habitual movements that are uncontrolled. Combining psychosis with tardive dyskinesia, and you get a term called 'punding', a compulsion to perform repetitive mechanical tasks.
See what i'm getting at here? This guy's punding is probably focused on compulsive gambling and sexual behaviour, which is again quite common. In regards to whether he's gay or not, the anecdotal evidence is that people develop compulsions to activities they already do (ie gardening, repair work etc) so it is possible he was already gay to start with. However, this cannot be absolutely proven.
What fascinates me the most is that this guy (and others) have successfully sued the drug company. If the side effects of these drugs are already so well known, surely he would have been warned. Possible explanations are that he was prescribed this medication off label as his Parkinson's was resistant to conventional treatment, or that he was not warned about the gay sex addiction specifically.
Speaking personally, the prescription of these medications are a dilemma for us doctors, because there is a balance between disastrous side effects of medications and the devastating effects of Parkinson's Disease itself, particularly in young patients who lose all their independence from it. It is a sad situation either way for this patient, he faces a bleak future if his Parkinson's is so resistant.
Oh, and the last thing to consider is that this man might be developing a Parkinson's dementia explaining or amplifying these behaviours, which is possibly the worst scenario in this case.