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Comparing weight loss medication

Losing weight is not an easy task. The traditional methods of diet and exercise don’t always work for everyone. This can be frustrating, and while it’s important to remember that weight loss will always be a slow process, it can also be a relief to find out there are more methods than exercise and dieting available to you in the modern day. While having options is great news for anyone wanting to lose weight, it’s also important to make sure the method you choose is safe, sustainable and suits your individual needs. 

It’s impossible to effectively compare weight loss pills without knowing all of the most important information about each one. Patient information leaflets, scientific studies and other similar sources are not the easiest to navigate or understand, often containing confusing jargon and complex measurement methods. So that’s why we’ve decided to create this weight loss medication comparison guide and table, providing you with everything you need to know about some of the most popular weight loss pills and medications. 

Which weight loss medication is best? 

Weight loss medication comes in two forms in the UK: appetite suppressants, and medication that reduces the absorption of fat in the stomach. Many different medications and active ingredients are available to achieve these goals, but the types of side effects you may experience will differ according to the active ingredient, the dosage and the way the medication works to help you lose weight. 

When it comes to comparing weight loss medications, it can be difficult to assess which medication is the best. This decision usually depends on your personal requirements and preferences, which side effects you’d prefer to avoid and what your preferences for course length and intensity of treatment are. While medication is often dependent on what works best for the individual, we’ve compiled a list of factors that can help determine which medications stand out among their competitors. 

Weight Loss Medications
NameAlliDiethylpropionMysimba
Active IngredientOrlistatDiethylpropionNaltrexone, Bupropion
FormCapsuleTabletTablet
FunctionReduces fat absorption of the stomachReduces appetiteReduces appetite
EffectivenessA 2021 review found that the active ingredient Orlistat reduced weight by 2.9% in 12 monthsA 2009 study found that subjects using Diethylpropion lost an average of 10.6% of their body weight after 12 monthsA 2021 review found that use of naltrexone/bupropion resulted in 4% of body weight lost in 12 months.
Price£39.99/month (based on 3 pack discount)N/A£99/month (based on 112 tablet pack)
Most Common Side Effects Flatulence, oily or soft stools, sudden bowel movementsFlatulence, constipation, indigestion, headaches, hair loss, drowsiness, dry mouth, muscle pain, stomach pain, skin rash, insomniaNausea, vomiting, constipation, headaches
Serious Side Effects*Severe allergic reaction, rectal bleeding, diverticulitis, pancreatitis, blisters, gallstones, hepatitis, kidney stonesFast or irregular heartbeat, blurred vision, heart, itching and rashes, difficulty breathing, chills, painful urination, chest pain, fainting, ankle or foot swelling, fever, sore throatSuicidal thoughts, seizures, serotonin syndrome, lupus rash, rhabdolmyolysis, Stevens Johnson syndrome, erythema multiforme
Average Drugs.com Rating6.28.7N/A
Is it available over the counter?YesNoNo
Weight Loss Medication
NameSaxendaPhentermineXenical
Active IngredientLiraglutidePhentermineOrlistat
FormInjectionCapsuleTablet
FunctionReduces appetiteReduces appetiteReduces fat absorption of the stomach
EffectivenessA 2021 review found that Liraglutide resulted in 5.4% of body weight lost in 12 monthsA 2021 review found that Phentermine resulted in 6.8% of body weight loss in 12 monthsA 2021 review found that the active ingredient Orlistat reduced weight by 2.9% in 12 months
Price£300/month from week 5 of treatment onwards (based on 5 pen discount)N/A£53.99/month (based on 3 pack discount)
Most Common Side Effects Flatulence, stomach problems such as bloating, discomfort, inflammation, pain and heartburn, weakness or exhaustion, dizziness, gallstones, insomnia, low blood sugar, increase in pancreatic enzymesDiarrhoea, constipation, stimulation, dry mouth, jitteriness, irritability, increased heart rateFlatulence, oily or soft stools, sudden bowel movements, headaches, diarrhoea, low blood sugar
Serious Side Effects*Severe allergic reactions, pancreatitis, thyroid tumours, low blood sugar, kidney problemsPrimary pulmonary hypertension, low blood sugar, heart valve diseaseSevere allergic reaction, kidney problems, liver problems, blood in urine, painful urination, lower back pain, stomach pain
Average Drugs.com Rating7.58.78.3 
Is it available over the counter?NoNoNo

*These side effects are listed under ‘serious side effects’ on the medication information leaflet, and if you experience them you should stop taking the medication and speak to your doctor immediately. In cases where serious side effects were not listed, we used information from drugs.com

It should be noted that some side effects are the result of conditions caused by the medication such as pancreatitis. Not all patient leaflets will categorise side effects by the condition that causes them, and as a result the number of side effects may differ between medications when recording the same condition. Consequently, the severity of side effects should be considered with more weight than the number of them. 

Which weight loss medication is the safest?

It can be difficult to determine which medications are safer than others, as this depends on the individual taking the medication, the number and severity of side effects, and how common serious side effects can be. Many medications list severe side effects for legal reasons without knowing how often they occur. With that in mind, we used the above factors to determine which weight loss medications may be considered safer to take than other medications. If you’re unsure about side effects and the safety of any particular medication, chat to your GP about your concerns. 

  • Alli and Mysimba appear to have the fewest common side effects (usually listed as side effects occurring in up to 1 in 10 people).
  • Alli is the only weight loss medication available over the counter in the UK, showing increased confidence in its safety. 
  • The medication with the fewest serious side effects appears to be Phentermine, although it should be noted that two out of the three serious side effects listed are potentially fatal conditions (primary pulmonary hypertension and heart valve disease).

What is the most effective weight loss medication?

The efficiency of weight loss medication can be measured in the percentage of weight loss that a subject experienced in a certain amount of time. These studies are often conducted in order to weigh the effectiveness of medication against the risks associated with using it, and they help to determine whether use of the drug is safe and worthwhile. We used two studies to determine which weight loss medication is more effective over a 12-month period: PubMed’s 2021 review of the long-term efficiency of active ingredients Orlistat, Phentermine, Liraglutide, and Naltrexone/Bupropion, and the International Journal of Obesity’s 2009 study on the effects of Diethylpropion. 

RankMedicationAverage weight loss over a 12-month period
1Diethylpropion10.6%
2Phentermine6.8%
3Liraglutide5.4%
4Naltrexone/Bupropion4%
5Orlistat2.9%
  • Diethylpropion appeared to be the most effective medication for losing weight over a 12-month period, with subjects losing 10.6% of their body weight. 
  • Phentermine is the second most effective appetite suppressant available, with subjects losing 6.8% of their weight in a year. 
  • Orlistat has a relatively low weight loss rate, with subjects losing 2.9% of their weight in 12 months. 

It’s important to note that different studies use different numbers of participants, which could provide differing results between studies. Despite this, placebo groups were present in all testing to ensure balanced and accurate results. It should also be noted that testing active ingredients may also cause differing results between the study and brand medication containing additional ingredients. 

Which weight loss medication is the cheapest?

Cheap diet pills and appetite suppressants within your price range are difficult to find. Diet medication is not often available on the NHS, making these treatments difficult to get hold of on a budget. So what are the best prices for weight loss medications in the UK? 

RankMedicationPrice per month
1Alli£49.99/month (based on 3 pack discount)
2Xenical£53.99/month (based on 3 pack discount)
3Mysimba£99/month (based on 112 tablet pack)
4Saxenda£300/month from week 5 of treatment onwards (based on 5 pen discount)
5Diethylpropion N/A*
6Phentermine N/A*

*Both Diethylpropion and Phentermine can only be prescribed by a doctor and must be used under supervision. Therefore, a price is not available for a specific dosage amount or length of course. 

The prices for Saxenda, Alli and Xenical are available in our online shop. As Mysimba is not available, we have used the price set by UK chain pharmacy Superdrug. 

What is the best weight loss medication on the market?

Experiences with weight loss medication vary depending on the individual. All factors need to be taken into account when determining the best weight loss medication for you, including which side effects you may prefer over others, how fast the medication works, what other measures are necessary to ensure efficient weight loss, and the price of the medication. When taking all factors into consideration, we found that: 

  • Appetite suppressants are more effective when it comes to long-term weight loss than anti-absorption pills. 
  • Appetite suppressants appear to be more expensive than anti-absorption pills, with Mysimba and Saxenda costing £99 and £300 per month respectively, compared to Alli and Xenical, which cost £39.99 and £53.99. 
  • Diethylpropion and Phentermine are the medications most highly rated on drugs.com, both achieving a rating of 8.7 from users. 
  • Diethylpropion and Phentermine have also been recorded to result in the most weight loss out of any medicine on the market, with Diethylpropion resulting in 10.6% of weight lost in 12 months, and Phentermine resulting in 6.8% in the same amount of time.

Which weight loss medication should I use? 

The best weight loss method and medication for you should be decided between you and your doctor. Many factors involved in choosing the correct medication are personal and individual, and what works well for someone else may not always be the best option for you. Hopefully this article has helped you make an informed decision about which weight loss medication to take. For more information about weight loss medications and methods, browse our blog here

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