An appetite-suppressant stimulant for short-term weight loss
Phentermine
An appetite-suppressant stimulant used for short-term weight loss alongside diet and lifestyle changes.
What is Phentermine?
Phentermine is a stimulant medicine that reduces appetite, used as a short-term aid to weight loss alongside a reduced-calorie diet and more activity. Because it is a stimulant, it raises the heart rate and blood pressure, so it is not suitable for people with heart disease or uncontrolled high blood pressure. It carries a risk of dependence and misuse, which is one reason it is meant for short-term use only. It is taken by mouth and used under medical supervision as part of a wider weight-management plan, not on its own.
Education and reference only. This is a plain-language guide to Phentermine — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Phentermine is a stimulant medicine used to suppress appetite as part of a short-term weight-management plan in people who are significantly overweight. It is intended to help someone stick to a reduced-calorie diet while they also make lasting changes to eating and activity, rather than being a long-term solution by itself. Because it is a stimulant with effects on the heart and circulation, and because it can be misused, it is used only for a short time and under medical supervision. It is taken by mouth, usually as a capsule or tablet.
How it works
Phentermine acts on the part of the brain that controls appetite, releasing signalling chemicals that reduce hunger and make a person feel full sooner, so they eat less. Because it works like a stimulant, it also speeds up the body in other ways, which is why it can raise the heart rate and blood pressure and cause restlessness or difficulty sleeping. Its appetite-reducing effect tends to lessen over time as the body adapts, which is part of why it is used only short-term, alongside diet and lifestyle changes that can be sustained.
Company & origin
Originated / developed by: Generic / specialist manufacturers.
A stimulant medicine that suppresses appetite, used only for short-term weight loss alongside diet and exercise.
Practical use
How to take Phentermine
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it by mouth as prescribed, usually earlier in the day to avoid sleep problems.
- Use it only for a short course, as advised, alongside a reduced-calorie diet and more physical activity.
- Tell your prescriber about any heart problems, palpitations or high blood pressure before starting, as it may not be suitable.
- Do not take more than prescribed and do not share it, as it can be habit-forming.
- Report any chest pain, a pounding or irregular heartbeat, breathlessness or mood changes promptly.
Weighing it up
Advantages & disadvantages of Phentermine
Advantages
- Reduces appetite and can help with short-term weight loss alongside diet and exercise.
- Taken by mouth as a simple once-daily medicine.
- Can give some people the initial push to start making lasting lifestyle changes.
Disadvantages
- Raises the heart rate and blood pressure, so it is not suitable for people with heart disease.
- Carries a risk of dependence and misuse, so it is for short-term use only.
- Commonly causes a dry mouth, restlessness, a faster heartbeat and difficulty sleeping.
Practical use
Good to know
The most important safety point is that phentermine is a stimulant: it raises the heart rate and blood pressure, so it is not suitable for people with heart disease, an irregular heartbeat or uncontrolled high blood pressure, and any chest pain, palpitations or breathlessness should be reported. It is intended for short-term use only, both because its effect wears off and because it carries a risk of dependence and misuse. It works best as one part of a plan that includes a healthier diet and more activity, not as a stand-alone fix. Common effects include a dry mouth, restlessness, a faster heartbeat and trouble sleeping, so it is usually taken earlier in the day. It should not be combined with certain other stimulants or with antidepressants of the MAOI type. It is used under medical supervision, with blood pressure and weight reviewed.
Who should not take it / use with caution
- People with heart disease, an irregular heartbeat or uncontrolled high blood pressure should not take it.
- People who have had a serious allergic reaction to phentermine should not take it.
- It must not be used with, or soon after, antidepressants of the MAOI type, because of the risk of a dangerous rise in blood pressure.
- It is avoided in pregnancy and breastfeeding, and in people with a history of significant mental-health problems or substance misuse.
Monitoring
- Checking blood pressure and heart rate before and during treatment.
- Reviewing weight and whether the medicine is helping as part of the wider plan.
- Watching for signs of dependence, mood changes or heart-related side effects.
Side effects
- A dry mouth, restlessness or feeling jittery.
- A faster or pounding heartbeat and a rise in blood pressure.
- Difficulty sleeping, headache, or mood changes such as anxiety or irritability.
- Rarely but seriously, chest pain, a very irregular heartbeat or breathlessness, which need urgent medical attention.
Key interactions
- It must not be combined with, or used soon after, antidepressants of the MAOI type, because of a dangerous rise in blood pressure.
- Other stimulants and some other weight-loss medicines add to its effects on the heart and should be avoided.
- Tell your prescriber about all medicines, including for blood pressure, mood and the heart, as several can interact.
Available as: Capsules and tablets taken by mouth.
Answers
Phentermine: frequently asked questions
What is phentermine used for?
It is a stimulant used to suppress appetite as a short-term aid to weight loss, alongside a reduced-calorie diet and more activity. It is not a long-term treatment on its own.
Why is it not for people with heart problems?
Phentermine is a stimulant that raises the heart rate and blood pressure, so it is not suitable for people with heart disease, an irregular heartbeat or uncontrolled high blood pressure.
Why can I only take it for a short time?
Its appetite-reducing effect wears off over time, and it carries a risk of dependence and misuse, so it is prescribed only for short-term use.
Why does it stop me sleeping?
As a stimulant it speeds up the body, which can cause restlessness and difficulty sleeping. It is usually taken earlier in the day to limit this.
Can I take it with antidepressants?
It must not be used with, or soon after, antidepressants of the MAOI type because of the risk of a dangerous rise in blood pressure. Always tell your prescriber what else you take.
Authoritative sources
- BNF
- NICE CKS
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