Semaglutide (SM-1)

What it is

Semaglutide is a man-made version of GLP-1, a hormone your gut releases after you eat. The natural hormone is broken down within minutes. Semaglutide was changed slightly so it lasts about a week, which is why the injection is given once a week.

How it works

GLP-1 tells your brain you’re full, slows down how fast your stomach empties, and helps your body release insulin when blood sugar rises. Semaglutide does the same, for much longer.

What studies found

• About half of the people on semaglutide lost 15% or more of their body weight. On placebo, fewer than 1 in 20 did.
• A once-a-day pill version led to 13.6% weight loss over 64 weeks in the OASIS 4 trial, compared with 2.2% on placebo.

What we don't know yet

• Why some people lose a lot of weight on it and others very little.
• How to keep the weight off after stopping: most people regain much of it.
• Effects over decades. The largest trials followed people for a few years.

Known risks

• Less common but serious problems include inflammation of the pancreas (pancreatitis) and gallbladder problems.
• In the US the label warns about a type of thyroid tumor seen in rodents, so people with a family history of medullary thyroid cancer are told not to use it.
• Weight usually comes back after the medicine is stopped.