Are you sure its not horse tranquilizer? or some other garbage?
Anyway, search Retatrutide studies from Lilly, NIH, or New England Journal of Medicine. They comment/report on the dosage tried so far by Lilly, over how many weeks, body mass lost, side effects, etc. Lilly will use the results to get approval from FDA. Dosage will have to be close to the studies to get approval.
Lilly tested: 1mg, titrating 2 to 4mg, 2 to 8mg, 4mg, titrating 4 to 8mg, titrating 2 to12mg. Half life is 6 days. The research results are only a guide so your lab rat shows similar results. As the product is not commercial yet, look at side effects, hours of research on lyophilization, excipients, storage, Hospira, sterilization, RN 101, ISR, effect on heart rate, etc. Not just dosage.