There are various side effects of Zoladex treatment that need to be watched out for and treated as far as possible.
Zoladex causes complete loss of libido and can cause higher cholesterol, raised blood pressure, lowering of bone density, weight gain and pain in joints and legs. By lowering testosterone it also causes fatigue and is not great for your head.
So far as I know, nobody on this forum has used weight loss drugs to counter any weight gains but even if it did help on that score it would be unlikely to counter any of the other effects listed above.
How long is your partner going to be on Zoladex? Many people now are not going beyond 2 years because the figures for long term survival aren't much different between 18 months of treatment and 3 years. I know it's tough but staying active does help with some of the side effects and if he's not on Zoladex for life, there's light at the end of the tunnel in that it's possible to return to normal if testosterone returns after the treatment has stopped.
Jules