Weight, weight-loss medicines and your joints

Rheumatologists do not prescribe weight-loss medicines, and this page is not a way to get one: they come from GPs, specialist weight-management services and private clinics. Nor does arthritis make you eligible on the NHS by itself; that depends on your body mass index, together with, for the injections, at least one condition linked to weight, such as type 2 diabetes, heart disease or high blood pressure, and on local services. The page exists for three reasons. First, several rheumatological conditions are affected by weight. Second, many people with arthritis already use one of these medicines or ask about them. Third, starting one can change how the arthritis and its treatment behave. It sets out how weight and the medicines bear on your joints. It does not recommend that you take one, and the practice does not offer them.

Carrying extra weight is not a failing of character, and it does not make your joint pain your own fault: the genes you are born with, some medicines (some steroids and antidepressants among them) and health conditions such as an underactive thyroid can all make a healthy weight harder to keep. The aim of what follows is practical: to explain the joint side of a choice you make with your GP, and to see that your rheumatology team knows about it.

There are two routes by which weight acts on joints. The first is mechanical: every extra kilogram adds load to the knees and hips, and each step multiplies that load roughly fourfold at the knee, so losing excess weight is one of the most effective things a person with knee or hip osteoarthritis can do. The second is chemical. Fat tissue is active, releasing substances that promote inflammation, which matters for inflammatory arthritis; and in gout, losing weight brings the urate level down.

What to eat and how to move are covered in their own guides, and this one leaves them there. For what food can and cannot achieve, see diet and arthritis; for urate, alcohol and the danger of crash diets, gout and diet; and for why movement helps rather than wears joints out, arthritis and exercise. This page takes up the piece they leave out, the medicines.

This page covers three medicines, and they do not all work the same way; liraglutide, a daily injection of the same group as semaglutide, is also among NICE's options.

Semaglutide (Wegovy) belongs to the GLP-1 group. It mimics a hormone the gut releases after a meal, dulling appetite and leaving you full for longer, so that with changes to diet and activity you eat less and lose weight. It is usually a weekly injection, and a tablet form also exists.

Tirzepatide (Mounjaro) works on two gut hormone receptors, GLP-1 and GIP, rather than one. Its effect is of the same kind, on appetite and fullness, and it too is injected once a week. Indirect comparisons in NICE's appraisal suggest that tirzepatide brings more weight loss than semaglutide.

Orlistat takes a different route altogether. Appetite is untouched; instead, less of the fat you eat is absorbed, and about a third of it leaves the body in the stools. It is an older medicine, generally produces more modest weight loss, and when people do stop it, its effects on the bowel are the most common reason.

The history of weight-loss medicines is uneven. Earlier drugs were taken off the market as their harms came to light: fenfluramine for damaging heart valves, sibutramine for its cardiovascular risk and rimonabant for serious effects on mood. None of the three is prescribed for weight loss now, and today's medicines are different molecules, but the record is a reminder that these are powerful medicines that need proper supervision. For the same reason, buy only through a registered pharmacy, since counterfeit weight-loss medicines are sold online.

The NHS rules on prescribing them keep changing, so this page sticks to what will last. Prescriptions come from GPs, specialist weight-management services and private clinics; eligibility, the choice of medicine and its funding vary by area and are under revision as guidance changes. Your GP or a weight-management service can tell you how things stand now.

Losing weight helps osteoarthritis of the knee and hip, and the evidence for it is firm. Losing excess weight lessens pain and helps the joint work better, and NICE's guidance places weight management, with exercise, at the core of treatment rather than at its edges. The logic is simple: each step puts less load through a worn joint when there is less weight to carry.

The medicines' best evidence in arthritis lies here. In a large trial published in 2024, people with obesity and knee osteoarthritis given semaglutide lost a substantial amount of weight, and their knee pain and function improved by worthwhile amounts compared with placebo. It is an important study, but it was not built to show how much of the improvement came from the weight lost, and whether the medicine does anything for the joint beyond that is still unclear.

In gout weight counts for a great deal, and there is a trap to know about before you start. Over time, losing surplus weight brings urate down and makes attacks less frequent, so it ranks among the most useful things someone with gout can do.

The trap is timing. Losing weight fast can raise the urate level for a while and bring on a flare before the benefit arrives, the same effect our gout and diet guide describes for crash dieting and fasting. With these medicines, the evidence so far is a small case series of four people, three of whom had a rise in urate in the first months and two of whom had flares; in a large trial of tirzepatide, urate fell over the 72 weeks compared with placebo. So lose weight, but do it gradually, and stay on any urate-lowering medicine you take. If you have gout and start one of these medicines, be ready for a flare in the first months: settle with your GP or team how one would be treated, and have the gout guide's flare advice to hand.

In rheumatoid arthritis, weight plays a quieter part. Excess fat tissue feeds inflammation, and higher weight goes with more active disease and, with some treatments, certain biologics among them, a poorer response than expected. Losing excess weight may therefore help bring the disease under control, which earns it a place in the wider plan.

Past that point, nobody yet knows. Researchers are interested in whether the medicines dampen inflammation themselves, beyond what weight loss achieves, but the evidence so far comes from observational studies and settles nothing. They should not be thought of as arthritis treatments, and they cannot take the place of a disease-modifying medicine. Methotrexate, the biologics and JAK inhibitors and the other treatments that control the disease are still the treatment; any weight-loss medicine you and your GP settle on may help the wider picture without replacing them.

These medicines carry cautions like any effective treatment, and several matter more when you have a rheumatological condition.

• The gut bears the brunt. Feeling or being sick, constipation and diarrhoea are common with the injections, and tummy pain with tirzepatide; with orlistat the effects are on the bowel, oily stools and needing the toilet suddenly among them. They can overlap with an arthritis medicine's side effects. Short of the signs in When to seek help, a pharmacist or your doctor can help with side effects that trouble you or do not settle; tummy pain that lasts or keeps coming back, sickness or diarrhoea with signs of running short of fluid, and bleeding from the bottom on orlistat are for the same day, as the list under When to seek help says.
• Muscle can go with the fat. Some lean tissue can be lost along with fat, so enough protein and regular strengthening exercise are worth the effort, and arthritis and exercise is a useful companion to this page. Eating less also means asking your healthcare team whether your diet still gives you the nutrients you need.
• Weight often comes back. Many people put weight back on after stopping, which is why follow-up carries on after the medicine ends and why habits formed while taking it matter. Do not stop abruptly without speaking to your doctor, especially with type 2 diabetes.
• Pregnancy and contraception. The injections are not taken in pregnancy or while breastfeeding, and orlistat is not taken in pregnancy and not usually while breastfeeding; semaglutide is stopped at least two months before trying to conceive and tirzepatide at least four weeks before, and if you become pregnant while taking any of them, tell the doctor who prescribes it. Tirzepatide can make the contraceptive pill less reliable, so an extra barrier method such as condoms is advised for four weeks after starting and after each dose rise; with orlistat, severe diarrhoea, or diarrhoea lasting more than a day, can do the same. Tirzepatide can also affect how well HRT tablets are absorbed, so patches or gels may be suggested instead. Arthritis treatment around pregnancy is covered in arthritis, autoimmune conditions and pregnancy.
• Little is known about combining them with arthritis treatment. Research on these medicines alongside DMARDs and biologics is thin. That calls for care, not alarm: speak to your rheumatology team before you start, and keep up your usual monitoring.

No single point here decides for or against a medicine; together they are reasons to choose carefully, with a prescriber who knows your history.

Most side effects of these medicines are for your pharmacist or prescriber to advise on. A few are not; for those, the lists below name where to go, beginning with the most serious.

Treat any of these as a 999 or A&E emergency: call 999 and do not drive yourself to A&E.

• Severe illness with suspected sepsis: a high fever with shaking, confusion, rapid breathing, or feeling dramatically worse over hours
• With a fever or feeling unwell, a rash that does not fade when you press it, a stiff neck with eyes that cannot bear bright light, or skin, lips or tongue turning blue, grey, pale or blotchy, since these can be signs of meningitis or sepsis, as can a very bad headache, confusion or a first seizure with a fever or feeling unwell; on black or brown skin the rash and the change of colour may be easier to see on the palms of the hands or the soles of the feet
• Sudden severe pain in the abdomen or back, or pain that spreads from the tummy to the back with being sick, or tummy pain with a very high temperature or with feeling hot, cold or shivery, or skin or the whites of the eyes turning yellow, since an inflamed pancreas or gallbladder, rare effects of these medicines, needs treatment in hospital
• Vomiting blood, or bleeding from the back passage that is heavy or will not stop, most of all with faintness, confusion or pain in the abdomen, or vomit that is black or dark brown, since orlistat can sometimes cause bleeding from the bottom
• Lips, mouth, throat or tongue that suddenly swell, a throat that feels tight, very fast breathing or a struggle to breathe or to swallow, skin, tongue or lips turning blue, grey or pale (on black or brown skin this may be easier to see on the palms of the hands or the soles of the feet), becoming suddenly very confused, drowsy or dizzy, or fainting and not being able to be woken, since this can be a severe allergic reaction, anaphylaxis, which can follow a dose of any medicine
• An eye that suddenly and completely loses its sight

Any of these needs an assessment that is urgent, on the same day, from your GP or NHS 111:

• Tummy pain that lasts longer than half an hour, or that keeps coming back, since gallstones or an inflamed pancreas have to be ruled out; sudden, severe pain, or tummy pain with a very high temperature or with feeling hot, cold or shivery, belongs to the first list
• Being sick or having diarrhoea that will not settle, with dizziness on standing that does not pass, dark yellow urine, passing less urine than usual, a fast heartbeat, or tiredness out of the ordinary, since the body may be running short of fluid; with confusion, drowsiness, fast breathing or difficulty breathing, or skin, lips or tongue that are cold, blotchy or turning blue, grey or pale (on black or brown skin this may be easier to see on the palms of the hands or the soles of the feet), this is a 999 or A&E emergency
• Low blood sugar (a hypo), with shaking, sweating or a racing heart, while you take one of the injections, since they can cause it, more often when taken with a diabetes medicine; if you have diabetes, tell your diabetes care team too, especially if hypos come often, at night or have been severe
• A raised, itchy rash after a dose, beyond any itch or redness where you inject, with none of the signs in the first list, since it can be an allergic reaction to the medicine
• Bleeding from the bottom while you take orlistat, including black or dark red stools or bloody diarrhoea, since this is a serious side effect the medicine can sometimes cause; heavy bleeding, or bleeding that will not stop, belongs to the first list
• A new red, painful eye, or sight that has blurred, dimmed or changed, which needs an eye casualty or urgent eye clinic the same day, as does an eye that light hurts, since semaglutide can worsen diabetic eye disease, and sight that is lost suddenly and completely belongs to the first list
• Having taken more than your prescribed dose: NHS 111 can tell you what to do

Short of the signs in the two lists, a side effect that troubles you or does not settle is for your pharmacist or the doctor who prescribes the medicine, and a gout flare after starting one is dealt with as the gout guide describes. If you take methotrexate, another DMARD, a biologic or a JAK inhibitor, the warning signs that belong to each are set out in our guides to methotrexate, DMARDs and biologics and JAK inhibitors. If you cannot tell how urgent something is, asking is never a mistake.

If you remember one thing from this page, let it be that a weight-loss medicine is not something to keep from your rheumatology team. Because weight matters to joints, losing what is surplus may ease osteoarthritis, reduce the long-run burden of gout and help hold rheumatoid arthritis steady. The same change can also provoke a gout flare in the first months, may interact with your arthritis medicines in ways not yet worked out, and does not, on what is known now, treat the arthritis itself. Talk it over openly: your GP or a weight-management service prescribes these medicines and knows the current rules, your rheumatology team can weigh what they mean for your joints, and the treatment that controls your arthritis carries on throughout. Approached like that, weight becomes something you can work on with support, not something to tackle alone.

Could a rheumatologist prescribe me a weight-loss medicine?

No. GPs, specialist weight-management services and private clinics prescribe these medicines, rheumatologists do not, and arthritis does not by itself qualify anyone for one on the NHS. If you would like to discuss one, start with your GP or a weight-management service. Tell your rheumatology team before you start, or as soon as you can if you already take one, since it can bear on your arthritis and on how it is treated.

Are weight-loss medicines a treatment for arthritis?

Not in themselves. The benefit to joints so far seems to come mainly through the weight that is lost: less load on knees and hips, and a lower urate level in gout. Whether these medicines quieten arthritis or inflammation by some other route is still being researched and is not established. Keep up the treatment for your arthritis, DMARDs or biologics for example, as prescribed; a weight-loss medicine cannot replace it.

Will a weight-loss medicine set off my gout?

It may, early on, so plan for it. Over months and years, losing weight brings urate down and makes flares rarer. In the shorter term, losing weight fast can lift urate for a while and trigger an attack, as a crash diet can, and flares in the first months of these medicines have been reported, so far in a small case series. The answer is to lose weight gradually and to stay on any urate-lowering medicine, not to avoid losing it. The crash-diet warning is explained in gout and diet, and what to do when a flare starts in the gout guide.

Is losing weight worthwhile for knee osteoarthritis?

Yes, and the evidence is strong. Shedding excess weight lessens pain and improves how a knee or hip with osteoarthritis works, which is why UK guidance puts it at the centre of treatment. In a large 2024 trial, people with obesity and knee osteoarthritis who took semaglutide lost a good deal of weight and had less knee pain than those given a placebo; the trial was not designed to show how much of that came from the weight lost, and whether the medicine helps the joint in any other way is still unclear. For the exercise side, see arthritis and exercise.

Is it safe to combine a weight-loss medicine with methotrexate or a biologic?

Talk it through with your team first, because the combination has had little study. Research on taking these medicines alongside methotrexate, biologics and other arthritis treatments is limited, so your rheumatology team should know before you start, and your usual blood tests and reviews carry on. Bear in mind too that these medicines are not taken in pregnancy, and the injections are stopped some weeks before trying to conceive; family planning is covered in arthritis, autoimmune conditions and pregnancy.