Phentermine Vs Orlistat (Xenical) For Adolescent Obesity

Is your teenager struggling with obesity? You’re not alone—adolescent obesity is a growing concern worldwide, whether in developed or developing countries.

When it comes to finding a solution, most experts recommend lifestyle changes first, but sometimes these alone aren’t sufficient.

While many of us prefer not to take medication, there are times when it becomes necessary, especially when weight gain affects daily life and self-confidence, and leads to health issues like diabetes, hypertension, and heart disease.

For parents, figuring out where to begin can be confusing and worrisome. Medications like Ozempic and Mounjaro are FDA-approved and effective for weight loss, but they can be expensive and not always prescribed by doctors for various reasons.

Among other options, phentermine and orlistat are also FDA-approved for weight loss.

So, which one is best for your teenage child? Let’s explore that next!

Read:

Rybelsus, Wegovy, Ozempic Vs Orlistat (Semaglutide Vs Xenical)

What is Orlistat (Xenical and Alli)?

This is a lipase inhibitor used to cause weight loss in obese people. You can find both the prescription, which comes in higher doses (Xenical), and over-the-counter (Alli) forms of orlistat.

It has minimal systemic absorption, so it acts locally within the gut. Thereby minimizing systemic side effects.

The impacts of orlistat in causing weight loss and improving any other comorbid conditions like HTN and T2DM are well-known through clinical trials.

Orlistat is popular for many reasons:

It is relatively cheap,
It has minimal systemic side effects,
Orlistat is approved only for weight loss,
There are cheaper brands available other than Xenical, and
It is also available as an OTC medicine.

What is Phentermine?

Phentermine is a sympathomimetic amine, a stimulant drug (like amphetamines). It is an appetite suppressant used to manage obesity in the short term.

In the USA, it is considered a Schedule IV controlled substance. This means it is regulated because there is some potential for abuse and dependence.

However, it’s important to know that Phentermine has a lesser risk of dependence compared to other stimulant medications [ref].

Phentermine is absorbed well by the body and reaches its highest levels in the blood within 3 to 4 hours after taking it.

After that, it stays in the body for about 20 hours, but this can be longer for people with kidney problems.

This works best when it is used with a weight loss diet plan that includes healthy eating, regular exercise, and lifestyle changes.

Phentermine is FDA-approved for weight loss in combination with Topiramate as Qsymia. It is not indicated alone for treating obesity.

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Side effects of Phentermine Vs Orlistat:

Orlistat is a relatively safer drug because it does not get absorbed. Phentermine is a stimulant drug and is not a good option for people with hypertension.

Side Effects of Orlistat (Xenical):

Oily stools or discharge from the rectum
Increased gas with bloating
Stomach discomfort or urgency
Headaches
Fatigue
Constipation

Side Effects of Phentermine:

Increased heart rate or blood pressure
Insomnia or trouble sleeping
Dry mouth
Headaches
Anxiety or nervousness

Read:

Mounjaro Vs Phentermine: Which is Best for Weight Loss

Mechanism of action of Orlistat Vs Phentermine:

Orlistat and Phentermine work differently. Both drugs are associated with weight loss, however, orlistat works by blocking fat absorption while phentermine suppresses appetite.

Mechanism of Action of Orlistat:

It works by blocking an enzyme lipase that is found in the digestive system. Lipoprotein Lipase is an enzyme that helps break down fats from the food we eat into mini molecules that can be absorbed by the body.

When Orlistat inhibits this enzyme, it prevents about 30% of the fat from being broken down and absorbed [ref].

Instead, the unabsorbed fat is excreted from the body in bowel movements and this helps reduce the number of calories absorbed, resulting in weight loss.

Mechanism of Action of Phentermine:

Phentermine works differently from Orlistat as it is an appetite suppressant that impacts the central nervous system.

Its mode of action involves stimulating the release of neurotransmitters, such as norepinephrine [ref], in the brain.

This increase in norepinephrine helps reduce appetite by making you feel full, which in turn helps you eat less.

Read:

The Weight Loss Effects of Rybelsus and Phentermine/ Topiramate

FDA Approval of Orlistat and Phentermine for Weight Loss:

Orlistat (Xenical) FDA Approval for Weight Loss:

The FDA approved it in 1999 for prescription as Xenical in the United States.

Its approval was based on clinical trials showing that it can cause weight loss when used in combination with a low-calorie diet [ref].

Phentermine FDA Approval for Weight Loss:

It was first approved by the FDA in 1959 to help people lose weight for up to 90 days.

Since then, its initial approval has not changed, and it was also approved to be used for a longer time in treating obesity when combined with topiramate, which is sold under the brand name Qsymia.

Read:

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Phentermine Vs Orlistat: Dosage and Administration

Both Phentermine and Orlistat are available as oral medicines. The dose and mode of administration are given below:

How to Take Orlistat (Xenical) for Weight Loss:

Prescription (Xenical):

120mg capsule taken three times a day with each main meal containing fat.

Over-the-counter (Alli):

60mg capsule taken three times a day with each main meal containing fat.

Mode of administration:

Orlistat capsules should be taken orally, either with a meal or up to 1 hour after a meal. The dose can be skipped if a meal is skipped or contains no fat.
To better tolerate Orlistat, it is best to start taking it with one of the major meals (once daily).
The dose is then increased to twice daily and then three times a day or with every major meal of the day.

How to Take Phentermine for Weight Loss:

It comes in various strengths, and your doctor will determine the specific dose based on your individual needs.

Usually, the starting dose is low and may be gradually increased if needed and tolerated.

Mode of administration:

It is typically taken once daily, either before breakfast or 1-2 hours after breakfast.
It is best to avoid taking it in the evening as it is associated with insomnia.

Read:

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Weight Loss Potential of Phentermine Vs Orlistat:

Orlistat is an FDA-approved weight loss drug. It is associated with 5 to 10% weight loss over 3 to 6 months.

In a 54-month trial period, Orlistat significantly reduced BMI and waist circumference in obese adolescents compared with a placebo [Ref].

However, there was not much difference in another 6-month study [Ref].

Phentermine is FDA-approved for weight loss in combination with Topiramate. In a clinical trial, Phentermine/Topiramate (Qsymia) resulted in a weight loss of 11.63 kgs vs 7.38 kg with phentermine alone over 28 weeks [Ref].

In another study, Phentermine/Topiramate resulted in a 5% weight loss in 75% of the study participants vs 44% in the Orlistat group [Ref]

Phentermine/Topiramate seems more effective for inducing and maintaining weight loss compared to Orlistat. Orlistat on the other hand is much more safer than Phentermine.

Read:

Wegovy Weight Loss Comparison with Other Weight Loss Drugs

Final Takeaway:

Orlistat (Alli or Xenical) is a safer drug for weight loss compared with Phentermine. In addition, phentermine alone is not approved for weight loss.

Phentermine use is a controlled drug (Schedule IV) and has the potential to be abused especially by teenagers.

Orlistat (Xenical, Alli) causes fat malabsorption and hence there is a risk of fat-soluble vitamin deficiencies.

Supplementation with Vitamin D, E, A, and K is required for patients on Orlistat.

Here is a table summarizing the PROS and CONS of Phentermine Vs Orlistat:

Factors	Orlistat	Phentermine
Mechanism of action	Blocks fat absorption in the digestive system but you must follow a low-calorie diet too.	Suppresses appetite by affecting brain chemicals so you won’t be hungry all the time.
Dose	Prescription: 120mg 3x daily, OTC: 60mg 3x daily	Varies based on individual needs
Side effects	Since it is not absorbed much, it does not cause as many side effects. The reported ones are mostly digestive issues.	It can lead to higher heart rate, insomnia, and anxiety, so younger kids must stay away.
Age limit	Approved for ages 12 and over	Not recommended for adolescents under 16
Long-term use	Generally well-tolerated for longer use	Limited data on long-term safety in adolescents

So, based on the available data, it appears that Orlistat will be a better option for your teenager, especially if he/she is younger than 16 years.

Orlistat does not cause severe side effects thanks to its mode of action and it can be used for a longer time period.

Meanwhile, phentermine is not even approved for teens below 16 years.

Nevertheless, this blog is only to help you understand how the two drugs differ, and it should not be taken as a replacement for professional advice. Your doctor should always be the one to make the final decision.