Health & Safety
Weight Loss Medication: Options, Eligibility and Safety
Prescription medicines can help some adults with obesity lose weight, alongside diet and activity changes. Here's who qualifies, how the main drugs work, what results to expect, and the safety rules.
In brief: weight loss medication is a prescription treatment for adults with obesity, or with overweight plus a weight-related health problem. In the US, doctors may consider it at a BMI of 30 or more, or 27 or more alongside a condition like raised blood pressure or type 2 diabetes. Used with a lifestyle program, these medicines lead to 3% to 12% more weight loss after one year than lifestyle changes alone. They don't replace healthy eating or activity.
Who Can Get Weight Loss Medication?
Doctors use body mass index (BMI) as the first check. The NIDDK, part of the US National Institutes of Health, gives these adult thresholds:
| Your situation | May be considered for medicine? |
|---|---|
| BMI 30 or above | Yes |
| BMI 27 to 29.9 with a weight-related condition (for example type 2 diabetes or raised blood pressure) | Yes |
| BMI 27 to 29.9 with no related condition | Usually a lifestyle program first |
| BMI under 27 | Not a usual use |
A high BMI alone doesn't mean you should take a drug. The NIDDK says these medicines are meant for people whose weight is affecting their health, and many people can lose weight with a structured lifestyle program. The NHS also bases access on your BMI and on any other conditions your weight affects, and a GP can refer you.
Four of these medicines are approved by the US Food and Drug Administration (FDA) for teenagers aged 12 and older. Treatment for anyone under 18 is a decision for their own doctor.
To see where you sit, work out your number with the BMI calculator. Our healthy BMI chart explains the bands and their limits.
What Medication Makes You Lose Weight?
Weight loss medicines work in one of two broad ways. Most act on appetite, so you're less hungry or fill up faster. One works in the gut, so your body absorbs less of the fat you eat.
The NIDDK lists the drugs the FDA has approved for long-term weight management:
| Generic name | How it's taken | How it works | Approved for |
|---|---|---|---|
| Semaglutide | Weekly injection | Copies the gut hormone GLP-1, which acts on appetite centers in the brain | Adults and ages 12+ |
| Tirzepatide | Weekly injection | Copies two gut hormones, GIP and GLP-1 | Adults |
| Liraglutide | Daily injection | Copies GLP-1 | Adults and ages 12+ |
| Phentermine-topiramate | Daily pill | Combines an appetite suppressant with a seizure and migraine medicine | Adults and ages 12+ |
| Naltrexone-bupropion | Pill, once or twice a day | Combines two medicines that may reduce hunger | Adults |
| Orlistat | Pill, three times a day | Cuts the amount of dietary fat your body takes in | Adults and ages 12+ |
| Setmelanotide | Daily injection | Targets brain pathways in four rare genetic conditions | Ages 6+ with a confirmed genetic cause |
Some versions of semaglutide, tirzepatide and liraglutide are also approved, at different doses, to treat type 2 diabetes. In the UK, the NHS describes the same groups: GLP-1 and GIP medicines such as semaglutide, tirzepatide and liraglutide, which reduce appetite, and orlistat, which reduces fat absorption.
Some appetite suppressants, such as phentermine on its own, are approved only for a few weeks of use. The NIDDK notes that little research has looked at their safety over longer periods.
How Much Weight Do People Lose?
Results depend on the medicine and on the person, but the averages are meaningful. According to the NIDDK:
- After a year, adults who add medicine to a lifestyle program lose an extra 3% to 12% of body weight, compared with people in the same program who don't take it.
- A share of people lose a tenth or more of the weight they began with. For some drugs, that applied to over half of trial participants.
- Most of the loss happens in the first 6 months.
Even a modest loss can matter. Losing 5% to 10% of your starting weight may lower blood sugar, blood pressure and triglycerides, and can ease joint pain and sleep apnea. The NHS gives the same 5% to 10% range as enough to improve your health.
Example: The 12-Week Check
The NIDDK says doctors usually review progress once you've been on the full dose for 12 weeks. If you've lost less than 5% of the weight you started at by then, stopping that medicine is the likely advice.
For someone who starts at 100 kg (220 lb):
- 5% of 100 kg = 5 kg (5% of 220 lb = 11 lb)
- So the target at the 12-week review is about 95 kg (209 lb) or lower.
If you're below that mark, your doctor may change your plan, try a different medicine, review other drugs that can cause weight gain, or discuss whether bariatric surgery is an option.
Weight Loss Medication Side Effects and Safety
Side effects vary by drug. The NIDDK says most are mild and tend to improve as treatment continues, but serious problems can happen, and in the past some weight loss drugs were withdrawn from US markets. That is why these medicines should never be taken purely for appearance.
Key safety points from the NIDDK and the NHS:
- Pregnancy: don't take them if you are pregnant or planning a pregnancy, as they may harm the baby. They also aren't recommended while breastfeeding.
- Other conditions: each drug has conditions that rule it out. For example, the GLP-1 medicines shouldn't be used by people with a personal or family history of medullary thyroid cancer or MEN 2. Naltrexone-bupropion shouldn't be used by people with uncontrolled high blood pressure, seizures, or anorexia or bulimia.
- Interactions: tell your prescriber about every medicine, supplement and herbal product you use. Don't combine weight loss medicines with other weight loss products unless a professional prescribes it.
- Mood: some people taking certain weight loss medicines have reported suicidal thoughts or actions. The FDA is still investigating whether the drug is the cause. Report any change in mood to your doctor.
- Supply: only use a pharmacy or online supplier that your prescriber has approved.
Over-the-counter products sold for weight loss are a different category. See whether weight loss supplements work for what the research shows.
How Long Do You Take Weight Loss Medication?
There's no fixed end date. If a medicine is working and you aren't having serious side effects, the NIDDK says your doctor may suggest staying on it long-term, because obesity is a chronic condition.
Expect some weight to come back if you stop. Keeping up healthier eating and regular activity can limit that regain. The NHS says you should be offered support to stay at a healthier weight after treatment ends. US federal guidelines advise at least 150 minutes of moderate activity a week plus 2 days of muscle-strengthening, and the NIDDK notes that some people need more than 300 minutes a week to keep weight off.
Limits and When to Get Advice
Only a doctor can decide whether a weight loss medicine is right for you. They will weigh the likely benefit against the side effects, your other conditions and medicines, and your family history. Speak to your doctor before starting, stopping or changing any medicine.
Get medical help promptly if you have side effects that are severe or don't settle, or any change in mood. Tell your doctor if you have, or suspect you have, an eating disorder. Some of these medicines are not suitable, and the NHS lists eating disorders as a reason to see a GP about weight.
Frequently Asked Questions
Can I get weight loss medication if my BMI is under 30?
Possibly. US guidance allows a prescription from a BMI of 27 if your weight is linked to another condition, like raised blood pressure or type 2 diabetes. Without a related condition, a structured lifestyle program is usually tried first. A doctor makes the final decision based on your overall health, not BMI alone.
Do I still need to diet and exercise on weight loss medicine?
Yes. Both the NIDDK and the NHS say these medicines work alongside healthier eating and more activity, not instead of them. Studies show they work best combined with a lifestyle program. The habits you build during treatment also help limit weight regain if you later stop taking the medicine.
Will I regain weight after stopping?
Most people regain some weight after stopping a weight loss medicine, according to the NIDDK. How much varies. Keeping up the eating and activity changes you made during treatment can help you regain less. Ask your doctor about a plan for stopping, and about support to maintain your weight afterward.
Is it safe to buy weight loss injections online?
The NIDDK's advice is to buy only from a pharmacy or online supplier that your prescriber has approved. These are prescription medicines with real risks and conditions that rule them out. A proper assessment by a prescriber who knows your medical history is part of using them safely.
To check whether your BMI falls in the range where medicine may be discussed, use the BMI calculator.
Sources
- Prescription medications to treat overweight and obesity (NIDDK, NIH)
- Treatment for overweight and obesity (NIDDK, NIH)
- Overweight and obesity in adults: treatments (NHS)
This guide is general information, not medical advice. It was written by the CaloriePro Editorial Team from the sources above; see our editorial policy. Speak to a doctor or registered dietitian before making big changes to your diet, especially if you are pregnant, under 18, or have a medical condition.