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The “Weight Loss Shot”: Ozempic, Wegovy, Mounjaro & Zepbound Explained

If you’ve been researching medical weight loss, you’ve probably heard patients and friends talk about “the shot” — a once-weekly injection that’s changed the way doctors treat obesity. But “the weight loss shot” isn’t one single medication. It’s a shorthand patients use for several different FDA-approved injectable medications, each with its own brand name, active ingredient, and approved use.

At St. Louis Bariatrics, we get asked about this every day: What’s the difference between Ozempic and Wegovy? Is Mounjaro the same as Zepbound? And is it safe to get a cheaper version from a spa or online pharmacy?

This guide breaks down what the weight loss shot actually is, how each FDA-approved medication works, and why we only prescribe FDA-approved products — never compounded versions.

What Is the “Weight Loss Shot”?

The weight loss shot refers to a class of medications called GLP-1 receptor agonists (and newer dual GIP/GLP-1 agonists). These drugs mimic hormones your gut naturally releases after eating. They work by:

• Slowing how fast food leaves your stomach, so you feel full longer
• Signaling your brain that you’ve had enough to eat, reducing appetite and food noise
• Helping regulate blood sugar levels

They’re given as a subcutaneous injection (similar to an insulin pen), typically once a week, usually in the abdomen, thigh, or upper arm. Most patients start on a low dose that’s gradually increased over several weeks to reduce side effects like nausea.

There are currently four FDA-approved injectable options on the market, built on two active ingredients: semaglutide and tirzepatide.

The FDA-Approved Options, Compared

Ozempic (semaglutide)

Ozempic is a once‑weekly semaglutide injection FDA‑approved for managing type 2 diabetes. Although many patients taking Ozempic also experience significant weight loss, it is not officially labeled as a weight‑loss medication. Ozempic contains the same active ingredient as Wegovy and is made by the same manufacturer, but it is offered in lower doses and is FDA‑approved specifically for glucose control in type 2 diabetes.

Wegovy (semaglutide)

Wegovy is also semaglutide — the same medication found in Ozempic — but it is FDA‑approved at higher weekly doses for chronic weight management in adults (and some adolescents) with obesity or overweight with a weight‑related condition. In addition, Wegovy is approved to reduce the risk of major cardiovascular events, such as heart attack and stroke, in adults with obesity and established heart disease.

Mounjaro (tirzepatide)

Mounjaro is a once‑weekly tirzepatide injection FDA‑approved for type 2 diabetes. It is made by Eli Lilly and works as a dual GIP/GLP‑1 receptor agonist, targeting two incretin pathways instead of one. Although its official indication is glucose control, many patients taking Mounjaro also experience significant weight loss. It contains the same active ingredient as Zepbound but is FDA‑approved specifically for diabetes management.

Zepbound (tirzepatide)

Zepbound uses the same medication — tirzepatide — but is FDA‑approved at different doses for chronic weight management in adults with obesity or overweight with a related health condition. In addition, Zepbound is approved to treat moderate‑to‑severe obstructive sleep apnea in adults with obesity. Like Mounjaro, it is a dual GIP/GLP‑1 agonist; the distinction lies in dosing and FDA‑labeled indications.

Quick Comparison

Ozempic vs. Wegovy: same active ingredient, different approved use and dosing — Wegovy is specifically studied and labeled for weight loss.

Mounjaro vs. Zepbound: same active ingredient, different approved use and dosing — Zepbound is specifically labeled for weight management and sleep apnea.

The right medication for you depends on your health history, insurance coverage, and treatment goals — which is why weight loss injections should always be prescribed after a medical evaluation by a weight loss physician office, not a quiz on a website.

Why We Don’t Prescribe Compounded “Semaglutide” or “Tirzepatide”

You may have seen ads for cheaper injectable weight loss products from med spas, wellness clinics, or online telehealth companies, often labeled simply “semaglutide” or “tirzepatide” instead of a brand name. These are usually compounded medications, or versions made by a compounding pharmacy rather than manufactured and tested by Novo Nordisk or Eli Lilly.

Compounding pharmacies were legally allowed to make copies of these drugs while Ozempic, Wegovy, Mounjaro, and Zepbound were on the FDA’s official drug shortage list. That shortage has ended, and the legal pathway that allowed most compounding has closed. Federal regulators tightened oversight of these products over the past year: tirzepatide came off the FDA’s drug shortage list in December 2024, and semaglutide followed in February 2025.[1] In April 2026, the FDA went further, proposing to permanently bar semaglutide and tirzepatide from the list of ingredients compounding facilities are allowed to use — which, if finalized, would close off most remaining legal compounding of these drugs.[1]

The safety concerns go beyond legality:

• No FDA review of safety or effectiveness. Compounded drugs skip the testing, manufacturing standards, and quality checks that brand-name medications undergo before reaching patients.
• Dosing errors. Regulators had logged over 455 adverse event reports tied to compounded semaglutide and more than 320 linked to compounded tirzepatide, with many involving patients drawing incorrect doses from multidose vials — some serious enough to require hospitalization.[2]
• Unproven additive combinations. Some compounders mix in additives like vitamin B12 or other ingredients. Research in 2026 found that combining tirzepatide with B12 can cause the two substances to chemically bond into a new molecule that doesn’t exist in the FDA-approved product and hasn’t been studied.[1]
• Sourcing and licensing gaps. A recent review found dozens of businesses still selling compounded semaglutide or tirzepatide after the shortage ended, and among the compounding pharmacies supplying them, some lacked the specific license required for sterile injectable compounding.[3]
• Misleading marketing. The FDA has sent warning letters to numerous telehealth and weight-loss companies for implying their compounded products are the same as the FDA-approved brand-name drug, when legally they are not.

None of this means every compounding pharmacy is unsafe or that every patient who’s used a compounded product has had a problem. But it does mean there’s meaningfully less oversight, less quality control, and less predictability than with an FDA-approved medication — and when a product is injected into your body, that margin matters.

Why St. Louis Bariatrics Only Prescribes FDA-Approved Medications

We prescribe Ozempic, Wegovy, Mounjaro, and Zepbound exclusively — never compounded semaglutide or tirzepatide. That means every patient gets:

• A medication manufactured under strict FDA quality and sterility standards
• Consistent, verified dosing in every pen
• A treatment plan backed by clinical trial data on both effectiveness and safety
• Support navigating insurance coverage and manufacturer savings programs, since cost is often the real reason patients consider compounded alternatives

Is the Weight Loss Shot Right for You?

These medications aren’t a quick fix, and they’re not right for everyone. A good candidate is typically someone with obesity, or who is overweight with a related condition like arthritis, back pain, high cholesterol, diabetes, high blood pressure, or sleep apnea. The medication works best as part of a broader plan that includes nutrition guidance, activity, and — for many patients — a longer-term relationship with a weight loss team who can adjust the plan as your body responds.

If you’re curious whether Ozempic, Wegovy, Mounjaro, or Zepbound could be a fit for your health goals, the first step is a consultation, not a quiz on the internet. Our team can review your health history, talk through what to expect, and help you decide which FDA-approved option makes sense for you.

Ready to talk to a provider about the weight loss shot? Schedule a consultation with St. Louis Bariatrics to get answers specific to your health and goals.

References

1. Stanford Medicine. “Compounded GLP-1s: Why doctors worry and the FDA is cracking down.” July 2026. https://med.stanford.edu/news/insights/2026/07/glp1s-compounded-why-doctors-worry-about-safety.html
2. Pharmacy Times. “FDA Moves to Permanently Close the Door on Compounded GLP-1s.” 2026. https://www.pharmacytimes.com/view/fda-moves-to-permanently-close-the-door-on-compounded-glp-1s
3. Med Matrix. “Is Compounded Semaglutide Safe? FDA 2026.” https://medmatrixusa.com/blog/fda-warning-letters-compounded-glp-1s

This article is for educational purposes and isn’t a substitute for personalized medical advice. Talk with a licensed healthcare provider before starting or stopping any medication.