Semaglutide comes two ways — a daily pill and a once-weekly shot. Here is what the trials measured.

The gist

Semaglutide is a medicine that copies a natural gut hormone called GLP-1 (glucagon-like peptide-1) — the signal your body sends after a meal to release insulin and tell your brain you're full. It comes two ways: a tablet you swallow once a day, and a shot you give yourself under the skin once a week. Doctors prescribe it for type 2 diabetes and for weight management, and big trials show it also lowers the odds of heart attacks and strokes in the right patients.

What do the studies show? In one large weight trial, people on the weekly shot lost about 15% of their body weight over roughly a year ^[1]. Most people also notice their constant thoughts about food go quiet. The flip side is real too — nausea is common at first, and there are cautions worth knowing. What people report and the honest downsides are on the effects page. This is a reading room, not a clinic: we summarize the published research and we don't sell anything or give medical advice.

What is semaglutide

Semaglutide is a GLP-1 receptor agonist — a lab-made copy of the gut hormone GLP-1, redesigned so it lasts far longer in the body. Native GLP-1 is gone from your blood in about two minutes; semaglutide hangs around for roughly a week. That's the whole trick behind once-weekly dosing.

How does it last so long? Chemists made two key edits to the peptide chain. They swapped one building block at position 8 for a sturdier one (called Aib) so the enzyme DPP-4 — the molecular scissors that chops up natural GLP-1 — can no longer cut it. Then they bolted on a long fatty-acid tail that grabs onto albumin, the most common protein in your blood, like a life raft. Riding albumin keeps semaglutide from being filtered out by the kidneys ^[5]. The molecule shares about 94% of its sequence with human GLP-1, so it still fits the same receptor perfectly.

The headline point for this site: the very same molecule is delivered two ways. The injection puts it straight under the skin. The tablet has to survive the stomach first, which takes a clever absorption helper — and that difference drives a lot of how each form behaves. We pull the two routes apart on the oral semaglutide page.

Two routes, one molecule

Here's the comparison this whole site is built around. Both forms contain the same drug, but they reach your bloodstream very differently.

The once-weekly injection. Given under the skin (subcutaneous), semaglutide is absorbed efficiently — roughly 89% of the dose reaches circulation. You dose once a week, and the trial doses for weight management top out at 2.4 mg once weekly ^[1]. This is the form behind the famous weight and heart-outcome trials.

The once-daily tablet. Swallowing a peptide is hard — your stomach is built to digest proteins, and a bare peptide would be destroyed. So oral semaglutide is co-formulated with an absorption enhancer called SNAC, which briefly nudges the local stomach environment to help a small amount of the drug slip through intact. Even with SNAC, oral bioavailability is only about 0.4-1%, which is why the tablet must be taken on an empty stomach with just a sip of water ^[8]. The trade-off is no needle.

Do the two forms work? Both do. The oral tablet at higher research doses (50 mg once daily) produced clinically meaningful weight loss in the OASIS program ^[9], and oral dosing improved blood sugar across the PIONEER diabetes trials ^[11]. The full breakdown — cadence, absorption, and what to watch for — lives on the Semaglutide research and oral semaglutide pages.

What the big trials measured

Few medicines have been studied as heavily as semaglutide. The evidence spans weight, blood sugar, the heart, the kidneys, and the liver — all from one receptor pathway.

Weight. In STEP 1, adults with overweight or obesity (no diabetes) on the once-weekly 2.4 mg shot lost a mean 14.9% of body weight at 68 weeks, versus 2.4% on placebo ^[1]. That's a roughly 12-percentage-point gap.

The heart. In SELECT, a 17,604-person trial of people with heart disease and obesity but no diabetes, the weekly shot cut major cardiovascular events (heart attack, stroke, cardiovascular death) by 20% versus placebo ^[3]. In people with type 2 diabetes, SUSTAIN-6 had earlier shown a similar 26% reduction in that composite ^[2].

The kidneys. In FLOW, in people with type 2 diabetes and chronic kidney disease, the weekly 1.0 mg dose cut major kidney events by 24% ^[6].

Head-to-head. In SURMOUNT-5, semaglutide was compared directly with tirzepatide in adults with obesity. Tirzepatide produced more weight loss at 72 weeks (-20.2% vs -13.7%) ^[7] — semaglutide's result was still large, just smaller than its newer rival. We unpack Semaglutide effects and the safety picture separately, because the benefits never come without the trade-offs.