Yes, orlistat and metformin can generally be taken together when a prescriber considers the combination appropriate for you. Orlistat has been studied in people with type 2 diabetes who were taking metformin, including people taking other diabetes medicines as well.
There is no established clinically relevant pharmacokinetic interaction between orlistat and metformin. The more practical issue is that both medicines can cause digestive side effects, and weight loss may affect blood glucose control. This means your diabetes treatment may need to be reviewed while you are taking orlistat.
This guide explains how the two medicines work together, what to know about side effects and vitamins, and what changes when you are buying Alli from a pharmacy or already using an injectable weight management medicine.
Key things to know
- There is no established clinically relevant interaction between orlistat and metformin. UK product information reports no observed interaction between orlistat and biguanides, the group of medicines that includes metformin.
- The main practical overlap is gastrointestinal side effects. Both medicines can cause digestive symptoms, so starting them at the same time can make it harder to work out which medicine is causing a new symptom.
- Weight loss can improve blood glucose control, which means your diabetes medicines may sometimes need to be reviewed.
- Metformin is not licensed as a weight loss medicine in the UK. It is authorised for the treatment of type 2 diabetes and can be used with other diabetes medicines when appropriate.
- Combining orlistat with an injectable weight management treatment is a separate question. There is limited evidence to support routinely using these treatments together, so this should be discussed with your prescriber.
Can You Take Orlistat With Metformin?
In many cases, yes, provided a healthcare professional considers it appropriate for you. People often ask, "Can I take orlistat with metformin?" or "Can you take orlistat and metformin together?" The answer depends on your overall health, other medicines and the reason you are taking each medicine.
The two medicines work in different ways. Orlistat works mainly in the digestive system by blocking enzymes called lipases. This reduces the digestion and absorption of some of the fat in the food you eat. Only a very small amount of orlistat is absorbed into the body.
Metformin helps lower blood glucose, mainly by reducing glucose production by the liver and improving the body's response to insulin.
Because they work in different ways, there is no established clinically relevant pharmacokinetic interaction between orlistat and metformin.
Orlistat Metformin Interaction Details
If you are searching for information about an orlistat and metformin interaction, the key point is that UK product information does not identify a clinically relevant interaction between the two medicines.
There Is No Established Pharmacokinetic Interaction
UK product information reports no observed interaction between orlistat and biguanides, the class of medicines that includes metformin.
This makes sense based on how the medicines work. Orlistat acts mainly in the digestive system and affects the digestion and absorption of dietary fat. Metformin works differently and does not rely on dietary fat for its action.
A 52 week clinical trial also studied orlistat in people with type 2 diabetes who were taking metformin alone or metformin with a sulphonylurea. The study found that adding orlistat alongside a reduced calorie diet and weight management programme was associated with greater weight loss and improvements in measures of blood glucose control compared with placebo.
The Real Overlap Is the Gut, and It Is Not an Interaction
This is the part that can matter most in everyday use.
Metformin can cause nausea, diarrhoea and abdominal discomfort, particularly when treatment is started or the dose is increased. Orlistat can cause digestive effects such as oily stools, an urgent need to open your bowels, wind with discharge and abdominal discomfort. These effects can be more noticeable after meals that contain more fat.
Because the side effects can overlap, starting both medicines at the same time can make it harder to work out which medicine is responsible if you develop new digestive symptoms.
If you are starting orlistat while already taking metformin, your prescriber or pharmacist can help you understand what to expect and what to do if side effects develop. Do not stop or change your diabetes medicine without medical advice.
Vitamins, Which Both Medicines Affect in Different Ways
Orlistat can reduce the absorption of fat soluble vitamins A, D, E and K. UK product information advises taking a multivitamin supplement at bedtime when using orlistat. For alli, the product information also recommends taking a multivitamin at bedtime.
Metformin can reduce vitamin B12 levels, particularly with higher doses, longer treatment and certain other risk factors. This is a separate issue from the effect of orlistat on fat soluble vitamins.
If you take both medicines, let your healthcare professional know about all the medicines and supplements you use. They can decide whether any monitoring or supplements are appropriate for you.
What Happens When They Are Used Together
The combination has been studied in people with type 2 diabetes.
A 52 week randomised, double blind trial studied people with type 2 diabetes and obesity who were taking metformin either alone or alongside a sulphonylurea. Participants received either orlistat or placebo alongside a reduced calorie diet and weight management programme.
| Outcome at 52 weeks | Orlistat added | Placebo added |
|---|---|---|
| Weight change | ~5.0% | ~1.8% |
| HbA1c change | ~1.1% reduction | ~0.2% reduction |
| Fasting plasma glucose | ~1.9 mmol/l | ~0.3 mmol/l |
| Waist circumference | ~4.8 cm reduction | ~2.8 cm reduction |
The study found greater improvements in weight, HbA1c, fasting plasma glucose and waist circumference in the orlistat group than in the placebo group. It also reported that people taking orlistat required less antidiabetic medication during the study.
These results come from a specific clinical trial and should not be taken to mean that everyone taking orlistat with metformin will have the same results.
Why Your Healthcare Professional Managing Your Diabetes Needs to Know
If weight loss improves your blood glucose control, your diabetes medicines may need to be reviewed and, in some cases, adjusted.
Metformin on its own does not usually cause low blood sugar. However, the risk of hypoglycaemia can be higher when metformin is used with medicines such as insulin or sulphonylureas.
This is why it is worth telling the healthcare professional who manages your diabetes before starting orlistat. They can decide whether your blood glucose monitoring needs to change and whether any of your diabetes medicines need reviewing.
If you take a sulphonylurea or insulin, make sure you know the symptoms of low blood sugar and what you should do if they occur. Never change your diabetes medicine yourself.
If you are taking orlistat, your response to treatment should also be reviewed. For prescription orlistat, UK product information recommends stopping treatment if you have not lost at least 5% of your starting body weight after 12 weeks. For alli, you should speak to a doctor or pharmacist if you have not lost weight after 12 weeks.
Because you have diabetes and are taking prescription medicine, your suitability for orlistat should be assessed using your full medical and medication history. Your GP or diabetes team can also help monitor your diabetes while your weight changes.
Can You Combine Orlistat With an Injectable Weight Management Treatment?
This is a different question from taking orlistat with metformin, so it is important to look at the evidence separately.
Injectable weight management medicines used in the UK include GLP 1 receptor agonists such as liraglutide and semaglutide, as well as tirzepatide, which acts on both GIP and GLP 1 receptors.
There is limited evidence to support routinely combining orlistat with another medicine specifically used for weight management. NICE guidance sets out the use of individual medicines for weight management rather than recommending routine combination treatment.
What Is Actually Known
There is not enough evidence to say that routinely combining orlistat with an injectable weight management medicine provides an additional weight loss benefit.
There are also practical considerations. Injectable medicines such as GLP 1 receptor agonists and tirzepatide can cause gastrointestinal side effects, including nausea, vomiting, diarrhoea and constipation. Orlistat can also cause digestive side effects, particularly when meals contain more fat.
Using the treatments together could therefore make digestive side effects harder to manage or make it more difficult to work out which medicine is causing a particular symptom.
If you are already taking an injectable weight management medicine, speak to your prescriber before adding orlistat. They can look at your current treatment, medical history and goals and decide whether using another medicine is appropriate.
An Injectable With Metformin Is a Different Matter
This is worth separating because the two combinations are sometimes confused.
Metformin is commonly used alongside some injectable diabetes medicines, including GLP 1 receptor agonists, when treating type 2 diabetes. That is different from combining two medicines specifically for weight management.
The fact that metformin can be used with an injectable diabetes medicine does not mean that orlistat should automatically be added to an injectable weight management treatment.
Can I Take Alli With Metformin?
Alli contains 60 mg of orlistat and is available from pharmacies without a prescription. It is a pharmacy medicine, so a pharmacist can assess whether it is suitable for you.
The interaction answer is the same as with prescription orlistat: UK product information does not identify an established clinically relevant interaction between orlistat and metformin.
However, there is an important practical point. If you are buying Alli from a pharmacy, tell the pharmacist that you take metformin and explain what you take it for. Also tell them about any other medicines or supplements you use.
The Alli product information advises people taking medicines for diabetes to speak to a doctor before starting treatment because weight loss can affect diabetes control and may mean that diabetes treatment needs to be reviewed.
So, if you have type 2 diabetes and are considering Alli, do not skip the pharmacy consultation just because it is available without a prescription.
What People Ask Online, and What Is Actually Established
Online discussions can be useful for hearing about other people's experiences, but they should not replace UK prescribing information or advice from a healthcare professional.
What is established is that UK product information does not identify a clinically relevant pharmacokinetic interaction between orlistat and metformin. There is also a genuine overlap in digestive side effects, and weight loss can mean that diabetes treatment needs to be reviewed.
A clinical trial has also studied orlistat in people with type 2 diabetes who were taking metformin, with or without a sulphonylurea. The trial found greater weight loss and improvements in some measures of blood glucose control with orlistat than with placebo.
What has not been established is that taking the two medicines together produces a special or synergistic effect, that one medicine needs to be timed around the other, or that either dose should automatically be changed because of the other.
If you read personal accounts online, they may give you an idea of what digestive side effects can feel like or how people manage their diet while taking orlistat. However, do not use someone else's dosing or medicine changes as a guide for your own treatment.
What to Tell Your Prescriber
- That you take metformin, including the dose and how long you have been taking it.
- Whether you take anything else for diabetes, particularly a sulphonylurea or insulin.
- Your most recent HbA1c result, if you know it, and any recent blood glucose readings.
- Every other medicine you take, because orlistat can affect the absorption of some medicines, including ciclosporin, warfarin and other oral anticoagulants, levothyroxine and some medicines used to treat HIV.
- Any digestive or absorption problems you have, as orlistat is not suitable for people with chronic malabsorption syndrome or cholestasis.
- Whether you are pregnant, planning a pregnancy or breastfeeding, as orlistat is not suitable in pregnancy and is not recommended during breastfeeding.
Medical Disclaimer
This page provides general information about taking orlistat alongside metformin and other treatments. It is not personal medical advice and does not recommend a dose for anyone.
Do not start, stop or change any medicine based only on this page, and never adjust your diabetes medicine yourself. If you take metformin, speak to the GP or diabetes team managing your diabetes before starting a weight management medicine.
Seek medical advice if you develop severe or persistent diarrhoea, symptoms of low blood sugar or other worrying symptoms. If you develop severe, persistent stomach pain, particularly if it spreads to your back and is accompanied by nausea or vomiting, seek urgent medical help. This can be a symptom of acute pancreatitis, which has been reported with GLP 1 receptor agonists and dual GLP 1/GIP receptor agonists.
Suspected side effects can be reported through the MHRA Yellow Card scheme.
