I personally believe you are right to be weary about holding off on long term use before the long term efficacy and risk profile of a drug has been established, but GLP1 class drugs have been around for a long time now.

GLP1 agonist type incretins have been available for over 20 years at this point. The first marketing approval was in 2005 for exenatide (Byetta), indicated for T2DM. Exenatide was the first in class for GLP1 agonists. Then came Liraglutide (Victoza) for the same indication around 2010, and received marketing approval for weight loss (as Saxenda) 4 years later. After that around 2017 was semaglutide (Ozempic & Wegovy).

T2DM is a chronic disease, so patients who started exenatide had to stay on it life long.

These drugs are nothing new and were already being used for T2DM. It only caught public attention because semaglutide achieved double the mean BW loss over liraglutide, making it meaningful for weight loss. Novo Nordisk first got approval for Ozempic for T2DM in 2017 and then received approval for it to be marketed for weight loss under Wegovy only in 2021, but by then clinicians were already prescribing it off-label, strictly speaking, for weight loss.

I don't know how much we could extend this "they've been around for a long time" to tirzepatide (Eli Lilly: Mounjaro & Zepbound) because it's the first dual agonist. It targets GLP1 and GIP, and thus it's meaningfully separated from the others. This goes for retatrutide (again Eli Lilly) as well if it eventually comes to market as it would be the first triple-agonist targeting the aforementioned + GCGR, the glucagon receptor.

Are there any cases of people upregulating too much in response to those agonists?