Phentermine & Diethylpropion

Both are prescription-only appetite suppressants acting on the central nervous system, but they're not interchangeable. Phentermine is usually taken once daily and tends to be tried first. Diethylpropion often comes in when Phentermine isn't suitable. A UK-registered clinician checks your BMI and history first.

Whether you are suitable for weight loss medication depends on your BMI, overall health, and a thorough clinical assessment—not a self-diagnosis. Many suitable candidates are adults living with overweight or obesity who have not achieved sufficient weight loss through diet and lifestyle changes alone. Certain heart conditions, high blood pressure, or conditions affecting the central nervous system may mean that medications such as Phentermine or Diethylpropion are not appropriate. Browse Weight Medics' weight loss treatment options to explore the medications and support packages available.

Dry mouth, trouble sleeping, a faster heartbeat, headaches, and mild stomach upset are common since these tablets stimulate the nervous system. Things usually settle within a week or two. Weight Medics builds in a two-week review, then regular check-ins, so any lingering issues get caught and adjusted early rather than ignored.

There's no specific amount. Everybody is different. NICE guidelines say losing 5% of your body weight  at 12 weeks can make a big difference to diabetes, blood pressure and joint pain. These tablets help by easing cravings so that a lower-calorie diet seems manageable. Patient stories show real results.

You’ll need a thorough consultation (typically via video) where a clinician will evaluate your health and weight. Once approved, medication is delivered securely to a UK address. “It’s not safe and it’s not legal to buy these controlled tablets without medical oversight. Instead, begin with a physical exam.

They can be, especially if you'd rather take a tablet than have injections, or you're not eligible for GLP-1 treatments. Unlike Mounjaro (Tirzepatide)  or Wegovy (Semaglutide), they work on hunger through the nervous system, not gut hormones so some medical conditions means we can not start patients on Phentermine or Diethylpropion  Compare both routes on the Weight loss injection packages page.

It's important to ensure 12 weeks of continual treatment, and a two-week break is then usually suggested to ensure tolerance to the medication doesn't build. 

Yes, Phentermine is legal, though it often gets mistaken for something banned. It is classed as an unlicensed medicine, which means it does not carry a standard MHRA licence but can still be prescribed by specialist clinics working under strict regulatory agreements. Your GP cannot write this prescription, and no legitimate pharmacy will sell it over the counter. For the full picture, our guide on whether Phentermine is legal in the UK sets out exactly where the rules stand.

No. These tablets sit outside standard NHS prescribing, so a request for a prescription at your local GP surgery is not possible. They are prescribed on a named patient basis by specialist weight loss clinics registered with the CQC, following a full assessment of your health, BMI and medical history. Your GP can still be kept informed of your treatment throughout, which is standard practise at Weight Medics.

No, and this is one of the most important things to get right. Any website offering Phentermine or Diethylpropion without a thorough medical review is operating outside UK regulations, and there is no real way to know what you are actually receiving. A genuine consultation checks your blood pressure, heart health and full medical history before anything is prescribed, which protects you from the risks that come with unsupervised stimulant use.

Wegovy (Semaglutide) tablets are the main alternative, and they work in a completely different way. Rather than being a stimulant based tablet, Wegovy (Semaglutide) tablets mimic a natural hormone that curbs appetite and slows digestion, helping you feel fuller for longer. They suit patients who would rather avoid a stimulant based option, though they can bring nausea or digestive discomfort, especially when starting treatment. Your clinician can talk you through which option fits your profile best.

Phentermine and Diethylpropion work on the brain to reduce hunger, while Wegovy (Semaglutide) tablets work differently, mimicking a hormone that curbs appetite and slows digestion. That means the side effects differ too: Phentermine and Diethylpropion can bring a faster heartbeat or trouble sleeping, whereas Wegovy is more likely to cause nausea, especially when starting treatment. Neither option is universally better, it comes down to what your body responds to and what your clinician recommends after your assessment.

Generally, yes. Tablet packages tend to start at a lower monthly cost than GLP-1 injections such as Mounjaro or Wegovy, which makes them an appealing option for patients who are eligible for either route. Cost should not be the only factor though. Your BMI, health history and how your body responds to different mechanisms all play a part in deciding which treatment gives you the better long term result.

There is no single answer that suits everyone. Tablets like Phentermine and Diethylpropion tend to suit patients who prefer to avoid needles or who have a lower BMI without major related conditions, while injections are often considered for higher BMI patients or those with additional risk factors such as elevated diabetes risk. If you are still weighing this up, our guide on how to choose the best weight loss tablets in the UK is a useful place to start before your consultation.

New patients need to be under 18- 65 to start treatment. If you are already an existing patient on the medication, you can continue up to age 75. Age is only one factor though, your overall health still needs to support ongoing use.

Regular blood pressure and heart rate checks are carried out throughout your treatment, alongside your scheduled reviews. This allows your clinician to spot any changes early and adjust your plan if needed.

Phentermine and Diethylpropion are not suitable for everyone. They may not be recommended if you are pregnant or breastfeeding, have heart disease, uncontrolled high blood pressure, glaucoma, hyperthyroidism, depression or unstable mood or take certain medications. Your clinician will review your medical history to decide whether these tablets or an alternative such as Wegovy (Semaglutide) tablets is the safest option. 

Yes. Both are schedule 3 controlled drugs, prescribed only under strict medical oversight. They are used off licence under MHRA approved arrangements, meaning they can only be prescribed by specialist clinics following a full assessment, not by a GP or pharmacy directly.