Comparative pharmacokinetics: semaglutide vs tirzepatide vs retatrutide — need advice

From the other side of the consultation, briefly.

PK/PD modeling for the pharmacology: understanding the pharmacokinetics helps optimize dosing. Semaglutide:

• Tmax: 24-72 hours post-injection
• T½: ~168 hours (7 days) — enables weekly dosing
• Steady state: reached at 4-5 weeks
• Bioavailability (SubQ): ~89%
• Volume of distribution: ~12.5L (primarily plasma)

The albumin binding (>99%) is the key pharmacological innovation — creating a sustained-release effect from a single injection. Previous GLP-1 agonists (exenatide) required BID dosing due to rapid clearance.

Adding the clinical framing, because it changes how the question reads.

Amycretin (AMY/GLP-1 dual agonist) emerging data relevant to the pharmacology: Phase 1 showed -13.1% body weight at only 12 weeks, the fastest trajectory ever seen for an anti-obesity agent[1].

Amylin receptor agonism enhances satiety signaling through the area postrema and reduces glucagon secretion. Combined with GLP-1R agonism, this dual mechanism may produce even greater efficacy than current agents.

Early-stage data — interpret with caution. But the trajectory is extraordinary.

EndoResFellow said:

Amycretin (AMY/GLP-1 dual agonist) emerging data relevant to the pharmacology: Phase 1 showed -13.1% body weight at only 12 weeks, the fastest…

Second this. Posting only so the count is not one.

EndoResFellow said:

Amycretin (AMY/GLP-1 dual agonist) emerging data relevant to the pharmacology: Phase 1 showed -13.1% body weight at only 12 weeks, the fastest…

Coming at EndoResFellow’s question from a different direction. The dose-response is real but shallow at the top. Across STEP 1 and STEP 4 the gap between 1.7mg and 2.4mg is a couple of percentage points of body weight on average, and the average is carrying a wide spread — plenty of people at 1.7mg sit above the 2.4mg mean. If a dose is working and tolerable, "working" is the relevant variable, not "maximal".

Moderator note: a couple of off-topic posts removed.