I'm fascinated by this topic as I just saw a couple of suppliers offered a tirzepatide + retatrutide combo in what I thought was a reasonable ratio (3mg tirz/1mg retra). But that got me wondering if there would be any actual benefit to that.
Unless there's something I'm missing, since molecularly they are pretty similar, except for the obvious modification of retra also stimulating glucagon receptors, they both have a stronger affinity for GIP than GLP-1, and essentially compete for the same receptors.
In other words, if they are both injected, they'll tend to compete for the same receptors, except for the additional antagonism of glucagon receptors with retra.
Anyhow all that said, though intriguing, I'll like pass on that combo product.