saudigastro.com/patients/weight-loss-medicines-explained
This article is educational and does not replace your doctor's advice. Seek urgent care for any red-flag symptoms.
Drug class
Anti-obesity medicines (lipase inhibitor, combination centrally acting medicines, GLP-1 and GIP/GLP-1 receptor agonists)
Examples
Orlistat; naltrexone-bupropion; phentermine-topiramate (not available in every country, and availability in Saudi Arabia should be confirmed with your pharmacist); liraglutide; semaglutide; tirzepatide. Brand names differ by country and are only examples.
How it works
Orlistat blocks about a third of the fat in a meal from being absorbed, so it passes out in the stool. Naltrexone-bupropion acts on appetite and reward centres in the brain. Phentermine-topiramate reduces appetite through the brain. Liraglutide and semaglutide copy the gut hormone GLP-1, and tirzepatide copies both GLP-1 and GIP; they slow stomach emptying, increase fullness and reduce hunger. In large randomised trials (with diet and activity advice in both groups) the average extra weight loss compared with placebo was modest with orlistat (a few percent of body weight), moderate with liraglutide 3 mg (around 8% vs about 2.6% in the SCALE trial), and larger with semaglutide 2.4 mg (about 15% vs 2.4% at 68 weeks in STEP 1) and tirzepatide (up to about 20% at the highest dose at 72 weeks in SURMOUNT-1). Individuals vary widely, and some people lose much less. In the SELECT trial, semaglutide 2.4 mg lowered the risk of heart attack, stroke or cardiovascular death in adults with heart disease and overweight who did not have diabetes. These results come from industry-sponsored trials of 1 to 3 years; longer-term safety data are still being collected. In the AGA 2022 guideline, the use of such medicines alongside lifestyle change is suggested for adults with obesity, with semaglutide, liraglutide, phentermine-topiramate, naltrexone-bupropion and orlistat all considered.
What it treats
- Obesity and overweight with weight-related illness, as an addition to food and activity changes. Product labelling usually refers to a body mass index (BMI) of 30 or more, or 27 or more with a weight-related condition such as high blood pressure, type 2 diabetes, sleep apnoea or fatty liver. The exact approved indication of each product in Saudi Arabia is set by the SFDA label, and your doctor should check it with you.
- Some of these medicines are also approved for type 2 diabetes (for example semaglutide and tirzepatide at different brand-name products and doses); the diabetes and weight products are not interchangeable.
- Reducing heart risk in selected adults with established heart disease and overweight (semaglutide, based on the SELECT trial), and improving fatty liver inflammation in some people with MASH (semaglutide), according to the local label and your specialist.
- They are not for cosmetic weight loss in people without a medical need, and not for use in children or teenagers unless a specialist prescribes them. They do not suit people with a history of an eating disorder without specialist supervision.
How to take it
These medicines are prescription-only and need a doctor who knows your health. Your doctor sets the dose and the schedule; do not copy another person’s dose or buy pens online or from unlicensed sources, because counterfeit and unregulated copies have been reported in several countries, so buy only from licensed pharmacies. Orlistat is a capsule taken with meals that contain fat. Naltrexone-bupropion and phentermine-topiramate are taken by mouth. Liraglutide, semaglutide and tirzepatide are usually injected under the skin with a pen, with the amount increased step by step to lower stomach side effects. Eat smaller meals slowly, stop when full, avoid greasy or very rich food, drink fluids regularly, and keep enough protein (and add resistance exercise) to protect muscle. Weight-loss medicines work with, not instead of, changes in food, activity and sleep.
Common side effects
- Nausea, vomiting, diarrhoea, constipation, belly discomfort, reflux, burping and feeling too full (very common with liraglutide, semaglutide and tirzepatide, mostly during dose increases and often settling over weeks)
- Oily spotting, urgent or loose stools and wind with orlistat, especially after fatty meals
- Dry mouth, headache, trouble sleeping, raised heart rate or blood pressure and constipation with naltrexone-bupropion or phentermine-containing products
- Tingling, taste change and tiredness with phentermine-topiramate
- Tiredness, dizziness, hair thinning and injection-site reactions
- Loss of muscle along with fat (see below)
Serious side effects — call your doctor
Severe, persistent pain in the upper belly, sometimes spreading to the back, with or without vomiting
Could be pancreatitis (inflammation of the pancreas), which has been reported with GLP-1 medicines. Stop the injection and go to the emergency department; do not restart unless your doctor says so.
Pain in the upper right belly, fever, yellow skin or eyes, or pale stools
Gallstones and gallbladder inflammation are more common with rapid weight loss and with these medicines. Seek urgent medical care.
Repeated vomiting or diarrhoea with dizziness, very little urine or inability to keep fluids down
Dehydration can injure the kidneys. Seek urgent care.
Severe constipation with swollen belly and vomiting, or being unable to pass wind
Possible bowel blockage (ileus) or very slow stomach emptying. Go to the emergency department.
A lump or swelling in the neck, hoarse voice, trouble swallowing or breathing
GLP-1 medicines carry a warning about thyroid C-cell tumours seen in rodents; the risk in humans is not established, but they must not be used with a personal or family history of medullary thyroid cancer or MEN2. See a doctor promptly.
Swelling of the face, lips or throat, widespread rash or trouble breathing
Could be a serious allergic reaction. Call emergency services.
Low mood, thoughts of self-harm, new seizures, severe anxiety or marked behaviour change
Mood changes and seizures are warnings with some of these medicines (especially bupropion and topiramate). Seek help at once.
Sudden loss or blurring of vision, or new vision problems in someone with diabetes
Semaglutide has been linked with rare optic nerve problems and, in people with diabetes, with worsening of diabetic eye disease. Urgent eye review.
Shakiness, sweating, confusion or fainting if you also use insulin or a sulfonylurea (diabetes medicine)
Low blood sugar; your diabetes medicines may need adjusting by your doctor.
Interactions
GLP-1 and GIP/GLP-1 medicines slow stomach emptying, which can change how quickly some oral medicines are absorbed, and they can raise the risk of low blood sugar when combined with insulin or sulfonylureas. Tirzepatide may reduce the effect of oral contraceptive pills, so a non-oral or added barrier method is advised when starting and after each dose increase. Because of the risk of food or fluid remaining in the stomach, tell your endoscopy or anaesthesia team before any sedation or operation; current advice is individualised and may include a liquid diet beforehand or holding the dose. Orlistat can reduce absorption of fat-soluble vitamins (A, D, E, K) and of some medicines such as ciclosporin, levothyroxine and some anti-seizure medicines, and can affect warfarin control. Naltrexone blocks opioid painkillers, so tell every doctor you use it. Bupropion lowers the seizure threshold and is affected by many medicines, so it is avoided in seizure disorders and during sudden alcohol or sedative withdrawal. Topiramate and phentermine have other interactions. Always show your full medicine list to your doctor and pharmacist.
Monitoring
Your doctor checks weight, waist, blood pressure, pulse, blood sugar and, when needed, kidney function, liver tests and vitamins. Progress is reviewed after a few months; if you have not lost a meaningful amount (usually at least about 5% of body weight at the maintenance dose), the medicine is often changed or stopped, according to the product label. Because some weight lost is muscle (in trials, roughly a quarter to a third or more of the weight lost with semaglutide and tirzepatide was lean mass, which includes muscle), ask about protein intake, resistance exercise, and strength or body-composition checks, especially if you are older or already have low muscle.
When and how to stop
Stop and contact your doctor for any serious warning sign above. Do not stop on your own because of mild stomach upset without asking, but do not push through severe symptoms. Obesity is a chronic condition, and in trials most people regained a substantial part of the lost weight within a year of stopping (in the STEP 1 extension, about two-thirds of the weight lost was regained within a year). So the decision to stop, continue long term, lower the dose or move to another approach should be made with your doctor, with a plan for food, activity and muscle protection. Stop these medicines if pregnancy is planned or occurs.
Pregnancy & breastfeeding
Weight-loss medicines are not recommended in pregnancy: weight loss gives no benefit to the baby, and topiramate (in phentermine-topiramate) is linked with birth defects such as cleft lip. Use reliable contraception while taking them (see the tirzepatide note above), and stop them before trying to conceive; the washout time differs by medicine, so ask your doctor. Tell your doctor if you are breastfeeding.
In the Saudi context
Obesity treatment in Saudi Arabia is supported by the Ministry of Health and specialist clinics, but which products are registered by the SFDA, for which indication, and whether they are supplied or reimbursed, changes over time and differs between hospitals; ask your pharmacist or clinic to confirm. Be cautious with “slimming” products sold in shops, social media and online; the SFDA has repeatedly warned about products containing hidden drugs, and counterfeit injection pens are a recognised problem. If you fast in Ramadan on one of these medicines, speak with your doctor first: reduced appetite can make it hard to eat and drink enough at iftar and suhoor, and dehydration and low blood sugar (if you also take diabetes medicine) are real risks. Do not reduce protein; traditional dishes such as lentil soup, fish, chicken, eggs and laban can help meet protein needs.
Questions to ask your doctor
Save this list or print it before your appointment — doctors appreciate prepared patients.
- Am I eligible for a weight-loss medicine based on my BMI and health conditions?
- Which medicine suits me best, and which side effects should I expect?
- How will I protect my muscle, and should I see a dietitian?
- How long will I need it, and what happens to my weight if I stop?
- I have gallstones, pancreatitis, thyroid disease or a planned endoscopy or surgery. Is it safe?
- How do I take it safely in Ramadan, and where can I buy genuine supplies?
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Status: Approved for publication by SGA; individual clinician review is ongoing · Published 24/04/2026
For general education only; it does not replace your doctor’s advice. Individual clinician review of this guide is ongoing. SGA clinician? Review this guide