Semaglutide or tirzepatide: how we choose

Semaglutide acts on the GLP-1 receptor. Tirzepatide acts on GLP-1 and on a second gut hormone receptor, GIP, at the same time. That is the whole mechanistic difference, and it is genuine rather than marketing.

In trials, the dual-pathway medicine has generally produced larger average weight loss. Averages, though, describe populations rather than people. Individual response varies widely in both directions, and plenty of patients do very well on the single-pathway medicine.

Both are given as a weekly injection. Both start at a low dose and step up on a schedule. Both cause their side effects mostly through the same route, which is slowed gastric emptying, so the experience of taking them has more in common than the mechanism suggests.

If one medicine is poorly tolerated, or if a genuine plateau persists at a full dose with everything else in place, switching is reasonable. It is not an admission that the first attempt failed.

Switching is done deliberately: dose equivalence is not one-to-one between these medicines, so the second one starts at its own schedule rather than matching where you left off. This is one of the specific places where being managed by a clinician matters more than the prescription itself.

Before switching, the boring things get checked. Has the dose actually been escalated to target. Is protein intake adequate. Has activity dropped. Is sleep wrecked. Most apparent plateaus have an explanation that is not the medicine, and changing the drug without checking those repeats the plateau on a new prescription.

Judge cost per month over the whole plan, including reviews and any monitoring, rather than by the price of a single pen. Programmes priced attractively per month sometimes exclude the clinical care that makes the medicine work.

Where insurance covers one option and not the other, that usually settles it, and we will tell you plainly when it has. Where nothing is covered, we will be equally plain about the monthly figure before you start, because starting and stopping on cost grounds is the most common way these treatments are wasted.

We do not stock, sell or take a margin on compounded alternatives. The FDA has published specific concerns about unapproved GLP-1 products, and the cost saving is not worth the risk profile.