I was on Zoladex for 6 months.
It did have some side effects on me including, memory problems, sleep problems, (waking in the early morning repeatedly with difficulty falling back to sleep) anxiety attacks, and fatigue.
I think these might contribute to yr uncle's behavioural change. I'm told the effects last 6 months after the expiry / end of the 3 months of the last treatment, and that is what I have found.
Maybe you could try talking about it with your uncle.