The incretins in a nutshell.
Semaglutide, tirz and reta- there are others and some very cool ones in the pipeline like bioglutide.
Sema
- glp1 receptor agonist- very similar to human glp1 and nearly equally as potent. Increases insulin sensitivity through a variety of mechanisms, reduces glucagon, slows gastric motility, reduces appetite. The nausea on this bad boy is the worst, because its agonizing one pathway heavily the side effects can be bad. This drug binds multiple receptors in the brain, namely in the area postrema which induces nausea and in the mesocorticolimibic pathway. It appears to impact reward signalling in the nucleus accumbens and quite frankly looks like a real winner for addiction as well. I believe it is the strongest anti-craving drug seen for alcohol so far- in the preliminary studies, but it extends to all addiction. Huge cardiovascular benefits, modest lipid impact. The effects down stream and ubiquitous.
Tirz
- glp1ra and GIP agonist- its a weaker glp than sema and the GIP works in synergy with the glp to enhance most of the benefits. The workings of GIP are pretty complex, some drugs increase it and reduce body weight, some reduce it and have the same effect, the impact is polyvalent. The extra glp benefits are less nausea as it is a mild anti-emetic and that is may improve triglyceride reduction. In our body it inhibits hormone sensitive lipase but may increase it with a glp but the data is mixed. Much better for weight loss
Reta
triple agonist, only novel mechanism is the glucagon agonism. Its about 8.9 times weaker as a glp then sema and the highest gip activity, so its easier on the guts in some ways. The glucagon action, reduces liver fat dramatically, increase basal metabolic rate, increases hormone sensitive lipase, increase hepatic ketone production, increase contractility and rate of the heart and depletes liver glycogen. The best for weight loss
Some musings. A recent paper highlighted that exogenous ketone supplementation, namely beta hydroxy butyrate made reduce incidence of sarcopenia from these drugs- they are not inherently sarcopenic and a recent study showed improved muscle function in type 2s. If someone were to be on reta and ingest ketones they may see higher levels of muscle retention and ketone production.