Evidence at a glance
Human clinical evidence 3 of 3 (substantial), preclinical evidence 3 of 3 (substantial).
My read of the published evidence, not a rating of whether it works. Preclinical findings cannot establish human benefit.
What is semaglutide?
Semaglutide is a modified version of GLP-1, a hormone your intestine releases within minutes of a meal. Native GLP-1 survives in the blood for about two minutes before enzymes shred it. Useless as a drug. Novo Nordisk's chemists swapped amino acids to resist those enzymes and attached a fatty-acid chain that binds albumin, producing a molecule that lasts a week. The intellectual lineage runs back to exendin-4, a GLP-1-like peptide first found in Gila monster venom.
It is sold as Ozempic (type 2 diabetes), Wegovy (weight management), and Rybelsus (an oral tablet form), all authorized in Canada. As with every entry here, the authorization belongs to those specific products, not to the molecule name printed on an online vendor's vial.
Why researchers are interested
Semaglutide's GLP-1 receptor activation does several useful things at once. In the pancreas, it boosts insulin secretion only when glucose is elevated, which is why it rarely causes hypoglycemia on its own. In the stomach, it slows emptying. In the brain (hypothalamus, brainstem, and reward-related regions) it dampens hunger signalling and, in many users' telling, mutes the background hum of food preoccupation.
The receptor's presence in reward circuitry is what has widened the research agenda far beyond metabolism. If GLP-1 signalling modulates *wanting* in general, not just wanting food, it becomes a candidate for studying alcohol use and other compulsive behaviours. That work is early; the metabolic pharmacology is not.
Regulatory status
Semaglutide products are authorized by Health Canada, the FDA, the EMA, and other regulators for type 2 diabetes and chronic weight management, with the U.S. label later expanded to include cardiovascular risk reduction in certain patients. It is a prescription medicine everywhere it is legal.
Its popularity created a shadow market. Shortage-era compounding, counterfeit pens, and “research use only” powder all circulate under the same molecule name with none of the same oversight.
What human research shows
Semaglutide's evidence base is enormous. The SUSTAIN trials established glucose-lowering in type 2 diabetes. The STEP programme tested the higher weight-management dose: in STEP 1, adults with obesity lost roughly 15% of body weight on average over 68 weeks versus about 2% on placebo. Then came SELECT, a cardiovascular outcomes trial in over 17,000 people with obesity or overweight and existing cardiovascular disease, which found a roughly 20% reduction in major adverse cardiovascular events. That is evidence the drug changes hard outcomes, not just the number on the scale.
Kidney-outcome data in diabetic kidney disease added another endpoint. Side effects are dominated by the gastrointestinal cluster, and trials show substantial weight regain after discontinuation. The drug manages a chronic condition rather than curing it.
| Semaglutide | Tirzepatide | Retatrutide | |
|---|---|---|---|
| Receptors | GLP-1 | GIP and GLP-1 | GIP, GLP-1 and glucagon |
| Status in Canada and the US | Authorized (Ozempic, Wegovy) | Authorized (Mounjaro, Zepbound) | Investigational, Phase 3 |
| Furthest trial stage | Phase 3 plus the SELECT outcomes trial | Phase 3 (SURPASS, SURMOUNT) | Phase 2, 48 weeks |
| Average weight loss, headline obesity trial | About 15% (STEP 1) | About a fifth of body weight at the highest dose (SURMOUNT-1) | About one-quarter of body weight at the highest doses (Phase 2) |
| Hard-outcome data | Yes: fewer major cardiovascular events in SELECT | Sleep apnea benefit shown; outcome trials ongoing | None yet |
What early research shows
Animal and cell research on semaglutide now runs ahead of the label in intriguing directions: rodent studies of alcohol and nicotine intake, models of neuroinflammation relevant to Alzheimer's disease, and work on GLP-1 receptors in the heart and kidney. Some of this has already graduated to human trials; the rest remains hypothesis. A rodent drinking less alcohol on a GLP-1 drug is a reason to run a human trial, not a reason to conclude the effect exists in people.
What it's being studied for
Beyond its approved uses, researchers are investigating semaglutide for:
- Alcohol use disorder and other addictive behaviours
- Alzheimer's disease progression
- Chronic kidney disease outcomes
- Osteoarthritis symptoms in people with obesity
- Heart failure with preserved ejection fraction
- Long-term body-composition effects, including muscle mass
What remains uncertain
The open questions about semaglutide are mostly about time and breadth: what decades of continuous GLP-1 receptor agonism look like, who can eventually stop without full regain, and how to protect lean mass during large, rapid weight loss. That last question is a live one for anyone thinking about aging, where muscle is what keeps you independent.
Rare-event signals continue to be studied and debated as real-world use expands to millions of people. And the neuropsychiatric and addiction applications, however promising the anecdotes, still await definitive randomized answers.
What people report
The signature semaglutide anecdote is the silencing of “food noise.” People describe walking past the pastry case and simply not caring, some for the first time in their lives. Others report fatigue, nausea, or an unsettling indifference to eating at all. These reports track the trial data reasonably well, which is what you would expect for a drug with this much randomized evidence behind it.
Still, individual before-and-after stories bundle the drug with everything else that changed: diet, training, medical attention, motivation. The trials are the reason we know the molecule works; the anecdotes are just its most vivid illustrations.
Sources
- Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). New England Journal of Medicine, 2021.
- Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT). New England Journal of Medicine, 2023.
