Saxenda works by mimicking a natural gut hormone called GLP-1, which regulates appetite, blood sugar, and digestion. It is a daily injectable prescription medication containing liraglutide at a dose of 3 mg, and it reduces body weight primarily by making you feel less hungry and eat less food. In clinical trials, people taking Saxenda lost about 8% of their body weight over 56 weeks, compared to roughly 2.6% with a placebo.
How Saxenda Mimics a Natural Hormone
Your body naturally produces a hormone called GLP-1 (glucagon-like peptide-1) in the small intestine after you eat. GLP-1 signals your brain that food is on board, helps release insulin, and slows digestion. The problem is that natural GLP-1 breaks down in minutes, so its effects are fleeting.
Liraglutide, the active ingredient in Saxenda, is 97% identical to the GLP-1 your body already makes, with a small structural tweak that prevents your body from breaking it down quickly. This means a single daily injection keeps the hormone’s effects active for roughly 13 hours, long enough to influence appetite throughout the day. It also raises levels of leptin, a hormone that signals fullness, further reinforcing the feeling that you’ve had enough to eat.
What Happens in Your Brain
GLP-1 receptors sit in several brain regions that control hunger, fullness, and food reward. When Saxenda activates these receptors, it works on two distinct levels.
First, it targets neurons in the hypothalamus that act as your brain’s appetite thermostat. Saxenda activates cells that promote fullness while simultaneously quieting the neurons that drive hunger. Researchers have described this effect like pressing the brake pedal before you even reach the stop sign: the medication triggers a sense of “I’ve had enough” earlier in a meal, sometimes even before gut signals from food arrive. This is a learned, anticipatory form of fullness that kicks in with continued use.
Second, Saxenda influences the brain’s reward pathways. Brain imaging studies in people with obesity show that liraglutide dampens the brain’s response to images of high-calorie foods while actually enhancing its response to lower-calorie options. This shift helps explain why many people on Saxenda report that cravings for rich, calorie-dense foods simply feel less compelling.
How It Affects Digestion
Beyond the brain, Saxenda slows the rate at which your stomach empties food into the small intestine. At the 3 mg dose, gastric emptying is about 23% slower than normal. Food sitting in the stomach longer means you feel physically full for a longer stretch after eating. In studies, people on Saxenda reported higher fullness and satiety ratings after meals and ate roughly 16% fewer calories when allowed to eat freely.
This slower digestion is also the main reason nausea is the most common side effect, something covered in more detail below.
Effects on Blood Sugar
Saxenda also helps regulate blood sugar, which is useful because many people with excess weight have insulin resistance or prediabetes. When you eat, Saxenda prompts your pancreas to release more insulin in a glucose-dependent way, meaning it only boosts insulin when blood sugar is actually rising. At the same time, it suppresses glucagon, a hormone that raises blood sugar. The net result is smoother, lower blood sugar spikes after meals without the risk of dangerous blood sugar drops that some diabetes medications carry.
What Weight Loss Looks Like in Practice
In the largest clinical trial (known as SCALE), more than 3,700 adults with obesity or overweight plus a weight-related health condition took either Saxenda or a placebo for 56 weeks alongside a reduced-calorie diet and exercise. The Saxenda group lost an average of about 8% of their starting body weight, compared to 2.6% in the placebo group. That translates to roughly a 5.4 percentage-point advantage from the medication itself.
Weight loss with Saxenda is gradual. It is not primarily driven by burning more calories. Studies measuring energy expenditure found no meaningful increase. Instead, the weight comes off because you consistently eat less, driven by reduced appetite and earlier fullness at meals.
Who Can Use It
Saxenda is FDA-approved for adults with obesity (a BMI of 30 or higher) or adults with a BMI of 27 to 29.9 who also have at least one weight-related condition such as high blood pressure or high cholesterol. It is also approved for adolescents aged 12 and older who weigh more than 60 kg (about 132 pounds) and meet the BMI threshold for obesity. In all cases, it is intended as an addition to a reduced-calorie diet and increased physical activity, not a replacement for them.
How You Take It
Saxenda is a once-daily injection you give yourself using a prefilled pen. You inject it under the skin of your abdomen, thigh, or upper arm, and you can take it at any time of day regardless of meals. The injection itself uses a small needle similar to what people with diabetes use for insulin.
You don’t start at the full dose. The standard approach is a five-week ramp-up: you begin at 0.6 mg daily for the first week, then increase by 0.6 mg each week until you reach the maintenance dose of 3 mg by week five. This gradual escalation helps your body adjust and reduces the intensity of side effects, particularly nausea.
Before first use, pens need refrigeration (36°F to 46°F). Once you start using a pen, it stays good for 30 days at room temperature or in the fridge. Never freeze it.
Common Side Effects
Digestive issues are by far the most frequent side effects, and they stem directly from the same mechanisms that make the drug work: slower stomach emptying and altered gut signaling. In clinical trials involving more than 3,300 adults on Saxenda:
- Nausea affected 39.3% of people (versus 13.8% on placebo)
- Diarrhea occurred in 20.9% (versus 9.9%)
- Vomiting happened in 15.7% (versus 3.9%)
These side effects tend to be most pronounced during the first few weeks, particularly during dose escalation, and typically improve as your body adjusts. In adolescents, rates were even higher: 42.4% experienced nausea and 34.4% had vomiting. The gradual dose increase from 0.6 mg to 3 mg exists specifically to ease this transition period.
For most people, nausea is manageable and temporary. Eating smaller meals, avoiding very fatty or heavy foods, and staying hydrated can help. If side effects remain severe, some people stay at a lower dose for an extra week before moving up.