Here’s Why Using Phentermine for Weight Loss Isn’t the Best Idea
Takeaways
Phentermine is one of the oldest FDA-approved medications for weight loss, gaining recognition in 1959. The initial products combined phentermine with fenfluramine and dexfenfluramine. Unfortunately, researchers found these to cause cardiac complications such as valvular abnormalities in users. As a result, the FDA removed fenfluramine and dexfenfluramine from the market in late 1997.
Phentermine alone or in combination with topiramate is relatively safer. That is why the FDA re-approved the medication for short-term (3-month) weight loss use in 2012.
Like other weight-loss drugs, phentermine seeks to complement a healthy lifestyle—not replace it. It is available in 3 formulations (the first 2 of which are phentermine only):
Apidex: 15.0 to 37.5 mg/day once or twice daily formulation
Lomaira: An 8 mg, 3 times a day package
Qsymia: A phentermine/topiramte combination available in varying strengths; 3.75 mg/23 mg, 7.5 mg/46 mg, 11.25 mg/ 69 mg, 15 mg/92 mg
How does phentermine work?
Phentermine is structurally similar to amphetamines. Thus, it lowers appetite through its indirect sympathetic action.
In other words, phentermine triggers the release of noradrenaline, the 'fight or flight’ hormone that enables the body to react in emergencies. It achieves this by directing blood flow to essential organs such as the heart and brain. As a result, blood flows away from the gastrointestinal tract, suppressing appetite and promoting a feeling of fullness.
In addition, phentermine directly inhibits neuropeptide Y—the main hunger signaling pathway in the brain. This also reduces cravings and hunger.
Topiramate is an anticonvulsant often added to phentermine to boost weight loss. How it achieves this isn't precisely known, but studies attribute the effect to its appetite suppressive qualities.
Who is phentermine suitable for?
In general, anyone who has attempted to lose weight and could not achieve their target weight is a candidate for weight-loss drugs such as phentermine. More specifically, the FDA recommends phentermine for individuals with a BMI of more than:
30 kg/m2 or
27 kg/m2 and associated comorbid conditions such as diabetes
Using phentermine for weight loss
Obesity is a chronic condition with many causes. Thus, a multi-faceted approach works best to induce and maintain weight loss.
There's no denying diet and exercise are the cornerstones of any weight loss program. Yet studies show they can only help participants lose 5% of their body weight. More concerningly, the weight reduction isn't sustained either, with up to 90% of individuals regaining any lost weight.
On the other hand, research shows that individuals who supplement a healthy lifestyle with medication report losing more than 9% of their body weight, with some medications (e.g., semaglutide) boosting weight loss up to 15%. They are also successful in maintaining their weight 56 weeks later.
Phentermine and the keto diet
The ketogenic diet is a popular diet that promises dramatic weight loss. It aims to use a fat-rich diet to re-wire the body's metabolism to break down fat reserves. The standard keto diet contains 75% fat, 20% protein, and 5% carbohydrates.
Many believe that phentermine can boost keto diet results. However, the interaction between phentermine and a ketogenic diet remains unknown. Hard evidence evaluating this is severely lacking and it is impossible to comment on the safety of this combination—both short and long term.
Phentermine side effects
Phentermine is not a good option for those with underlying heart disease. It can cause a range of cardiovascular complications such as:
Strokes
Arrhythmias (irregular heartbeat)
Heart failure
Coronary artery disease
Valvular abnormalities
Uncontrolled high blood pressure
Other common phentermine side effects include:
Tingling or pin-like sensation in hands or feet
Insomnia
Constipation
Phentermine contraindications
Given phentermine sympathomimetic effects (i.e., it causes an effect similar to that produced by stimulation of the sympathetic nervous system), it can trigger hypertensive episodes. As such, phentermine is contraindicated in:
Hyperthyroidism
Pregnancy and breastfeeding
Glaucoma
Users of CNS stimulants
Patients using monoamine oxidase inhibitors, isocarboxazid, linezolid, phenelzine, and procarbazine
The phentermine-topiramate can also interact dangerously with commonly used anti-depressants—selective serotonin reuptake inhibitors (SSRIs)—to cause serotonin syndrome. This can lead to fever, sweating, tremors, diarrhea, agitation, irregular heart, unconsciousness, and even death.
Phentermine’s dark side: Weight loss that comes with a price
Despite phentermine’s purported benefits, we do not recommend phentermine for weight loss here at NOVI Health. Here’s are the top three reasons why.
Does not address the root cause
While phentermine is an effective weight loss drug and works by suppressing appetite, it does not influence the body's metabolism and genetics—which are responsible for more than 80% of body weight.
Does not support lasting weight loss
Data supporting the use of phentermine is scarce. To date, only 3 placebo-controlled trials exist. While participants of these trials do report weight loss, the results are short-lived. More specifically, one-third of all users regained their lost weight within a year after treatment discontinuation. While phentermine may help one achieve short-term weight loss, it achieves this without building healthy habits. Thus, weight rebound is likely to happen.
Can be addictive
Phentermine use is also associated with a range of side effects and complications. For instance, given phentermine's structural similarity to amphetamine, it carries an addictive risk.
Furthermore, cardiac arrhythmias, metabolic disturbances, and psychiatric impairment are common among users. That is also why the FDA does not recommend long-term phentermine use. On top of that, the drug is often associated with fetal abnormalities in pregnant women, such as cleft palate.
Thus given the unfavorable risk-reward ratio, we cannot recommend phentermine. GLP-1 receptor agonists such as liraglutide and semaglutide are safer, better alternatives that can help you lose weight and improve your metabolic profile, targeting the underlying biology of obesity. A large body of evidence supports their use with research indicating that GLP1-receptor agonists are safe, tolerable, and effective in reducing weight in individuals with obesity.
Saxenda (liraglutide) and Wegovy (semaglutide) would be better options for weight loss. In multiple clinical studies of Saxenda, using the medication consistently resulted in weight loss of 4 to 6 kg. Nearly two-thirds of patients lost at least 5% of their body weight, and nearly one-third lost at least 10%.
Meanwhile, with Wegovy (semaglutide), patients achieved 5%–20% or greater weight loss. Further, Wegovy was found not only superior at reducing body weight compared with other antidiabetic drugs, but also cardioprotective.
Further, semaglutide such as Wegovy can be used for long-term management of weight.
Looking to lose weight safely and sustainably? NOVI Optimum Plus is our weight loss program centered on safe and proven weight loss medications supported by a healthy lifestyle for weight loss that lasts.
This publication does not constitute an advertisement, and is intended solely for educational purposes. Please seek professional medical advice as to whether a health product would be appropriate for you.
