Many people see their skin sensitivity fade over time, so maybe try reducing to 3.5mg of reta for a couple weeks first. I haven't tried switching myself but I've considered it. You seem more reactive than average to reta, so start tirz at a low dose too in case you're sensitive there. Tirz suppresses appetite more strongly, not a direct swap. I'd drop reta by 0.5mg and add 0.2mg tirz in week one. Check how it feels and keep going weekly at similar increments. Tweak as necessary. Appetite should remain similar. Go at whatever speed feels right until you get the outcome you want. Update us on progress.
I've been dealing with skin sensitivity problems at 4mg of Reta. Began with 0.5mg eight months back and increased gradually. Planning to switch to Tirz hoping the issues resolve. What's a good way to begin transitioning?