Semaglutide vs Tirzepatide: How a Charleston Physician Decides Which Fits You

Ashley Harwyn, PA-C, ABAAHP  |  Published October 17, 2026  |  Last updated October 17, 2026  |  12 min read

The head-to-head numbers, the real side effects, and how a clinician matches the drug to the person, from a Mount Pleasant PA-C.

This is an honest, Charleston-based guide to the two most effective weight-loss medications available: what semaglutide and tirzepatide are, how they compare on real trial numbers, what the side effects and risks are, and how a clinician in Mount Pleasant or downtown Charleston actually decides between them for a specific patient rather than prescribing the one with the bigger headline.

• In the SURMOUNT-5 head-to-head trial, tirzepatide led to about 20.2% average body weight loss versus 13.7% for semaglutide over 72 weeks.[1] The trial average is a guide, not a guarantee for any one person.
• Semaglutide is a GLP-1 receptor agonist. Tirzepatide is a dual GIP and GLP-1 receptor agonist.[5][6] The second mechanism is part of why its trial numbers run higher.
• The brand name signals the approved use: Wegovy (semaglutide) and Zepbound (tirzepatide) are approved for weight management, while Ozempic and Mounjaro are the type 2 diabetes versions of the same two molecules.[5][6]
• Both share the same leading side effects, which are gastrointestinal: nausea, diarrhea, vomiting, and constipation.[7] Both carry a boxed warning for thyroid C-cell tumors and are not for people with a personal or family history of medullary thyroid cancer or MEN 2.[5][6]
• Compounded semaglutide and tirzepatide are not FDA-approved, and the shortages that drove that market ended in 2025.[8]
• The right choice depends on your diabetes status, your weight-loss goal, how you tolerate the drug, and your coverage, which is why this belongs with a clinician who runs labs, not a questionnaire.

What semaglutide and tirzepatide actually are

Both are once-weekly injections that quiet appetite and slow stomach emptying, but they are not the same drug. Semaglutide is a GLP-1 receptor agonist, meaning it mimics one gut hormone that signals fullness.[6] Tirzepatide is a dual agonist that acts on two receptors, GIP and GLP-1, and that second mechanism is a large part of why its trial results run higher.[5] Same weekly rhythm, different biology.

The brand name tells you the approved use, and this trips up a lot of people. Semaglutide is sold as Wegovy for chronic weight management and as Ozempic for type 2 diabetes. Tirzepatide is sold as Zepbound for weight management (and for moderate-to-severe obstructive sleep apnea in adults with obesity) and as Mounjaro for type 2 diabetes.[5][6] It is the same molecule inside each pair; the brand reflects the indication it was approved and studied for, which matters for both safety framing and insurance.

So when someone asks whether Ozempic or Mounjaro is better for weight loss, the cleaner question is semaglutide versus tirzepatide, prescribed under the brand approved for your situation. The molecule and the evidence are what matter, not the name in the ad.

Semaglutide vs tirzepatide: the head-to-head numbers

There is now a direct comparison, and it is the number everyone wants. In SURMOUNT-5, a 72-week randomized trial in adults with obesity and without diabetes, tirzepatide produced an average body weight reduction of about 20.2% compared with 13.7% for semaglutide.[1] A larger share of the tirzepatide group also hit the deeper targets: about 31.6% reached at least 25% weight loss, versus 16.1% on semaglutide.[2] On average, tirzepatide moved the needle further.

The table below puts the major trials side by side so the comparison is not just one study.

Read the numbers honestly. The highest tirzepatide figure, about 22.5% in SURMOUNT-1, is the result among people who stayed fully adherent to the dose; the figure for everyone assigned to it is closer to 21%.[3] Averages also hide a wide range: some people on semaglutide outlose some people on tirzepatide. The trial tells you the typical result, not your result, which is exactly why the choice is clinical.

Considering a GLP-1 in Mount Pleasant or downtown Charleston? The right start is baseline labs, a real history, and the drug matched to you, not chosen online. See how we run it on the medical weight loss page, or call 843-981-0870 to talk it through.

What the side effects and risks really are

The side effects are more alike than different, and they are mostly in the gut. For both drugs, the most common adverse reactions are nausea, diarrhea, vomiting, and constipation, which is why both are started at a low dose and stepped up slowly over months.[7] Neither label makes a head-to-head tolerability claim, so anyone telling you one is simply “easier on the stomach” is going beyond the evidence.

The serious warning is identical for both, and it is not optional reading. Both carry a boxed warning for the risk of thyroid C-cell tumors. The tirzepatide label states it plainly: “In rats, tirzepatide causes thyroid C-cell tumors. It is unknown whether ZEPBOUND causes thyroid C-cell tumors, including medullary thyroid carcinoma (MTC), in humans as the human relevance of tirzepatide-induced rodent thyroid C-cell tumors has not been determined.”[5] The semaglutide warning reads the same way.[6] Both are contraindicated if you have a personal or family history of medullary thyroid carcinoma or MEN 2, which is the kind of history a prescriber has to ask about before writing either one.

That is the real reason these are prescription medications and not a product you should buy from a website that never takes a history. The screening is the safety.

How a Charleston physician decides which fits you

With two effective options, the decision comes down to a handful of concrete factors, and bigger average weight loss is only one of them. Here is how a careful clinician weighs it for a specific person, rather than defaulting to the drug with the best trial number.

• Do you also have type 2 diabetes? That shifts the choice toward the diabetes-approved brand and changes how insurance treats it.[5][6]
• How much weight do you need to lose? For a larger goal, the SURMOUNT-5 average favors tirzepatide, a defensible reason to lean that way, stated as a trial average and not a promise.[1]
• How is your tolerance and titration going? Both share the same GI profile, so the right answer is often whichever one your body settles into at an effective dose.[7]
• What does your plan actually cover? Coverage and out-of-pocket cost frequently decide this in the real world, independent of which trial number is higher.
• Any thyroid or MEN 2 history? That rules out both and redirects the whole plan.[5][6]

At Solcara, medical weight loss for Charleston and Mount Pleasant patients starts with labs and a history, not a drug name chosen in advance. The medication is one piece of a plan that also protects muscle and tracks real body composition, because the goal is losing fat and keeping strength, not just a smaller number on the scale.

The compounded GLP-1 caution

There is a cheaper, online version of these drugs, and it deserves a clear warning. Compounded semaglutide and tirzepatide are not FDA-approved, which means no agency has reviewed them for safety, effectiveness, or quality before they reach you. The FDA puts it directly: “Compounded drugs are not FDA-approved. This means the agency does not review their safety, effectiveness or quality before they are marketed.”[8]

The compounding boom was largely a shortage story, and that story has ended. The FDA removed tirzepatide from its shortage list in late 2024 and declared the semaglutide shortage resolved in 2025, and it has since sent warning letters to telehealth companies still marketing compounded GLP-1s.[8] The approved, brand-name drug with a verified dose and a boxed-warning label is the safer product, and the price gap is not worth trading away that oversight when a clinician is involved.

Medical weight loss in Charleston and Mount Pleasant

The medication is the tool, not the plan. Across the Charleston area, GLP-1 programs range from careful, physician-led care to online services that mail a pen after a brief form. The difference that matters is whether someone runs baseline labs, screens for the contraindications above, matches the drug to your history, protects your muscle as you lose weight, and adjusts over time.

If you are in Mount Pleasant, West Ashley, Daniel Island, or downtown Charleston and want a GLP-1 program built around your labs rather than a one-size prescription, our guide to what GLP-1 weight loss costs in Charleston breaks down the drivers, and body composition testing explains how we confirm you are losing fat and keeping muscle. The medication choice, semaglutide or tirzepatide, is a decision to make with a clinician who knows your history, not a box to check online.