Losing weight while on prescription medication

Myself and partner are big fans of eating whatever you want, whenever you want - which for me in particular means when I'm not pregnant I stay within ~1kg of my natural weight, so it certainly works for me. His weight has been very slowly creeping up since we got together, but nothing dramatic. He's learnt how to make fantastic roast dinners and it shows :)

However, for the last few months he's been on anti-anxiety meds that have really messed with his metabolism. When he first went on them he dropped 5kg without doing anything, then gained 10 without doing anything. Now his dosage has changed he's hungry all the time (which kills the 'eat what you want' thing completely) and he's put several more kilos on in the last couple of weeks, which puts him at around 15kg over his ideal weight, and he's taken up a 4km walk every day in the last few weeks too so its not being sedentary, its definitely the drugs.

How do you deal with these side effects? Do you go see the doc and change/stop the meds, or fight them with some kind of appetite suppressant? Or just go hungry and modify your diet? This house is full of very high calorie food at the moment for my benefit and my portion sizes are obscene so this house is not an easy place to try and diet in.

We both need to lose weight but unfortunately I'm breastfeeding and the weight will come off without help so we can't really motivate each other at all.