Obesity is a widespread chronic disease with significant health risks, including diabetes mellitus, heart disease, hypertension, dyslipidemia, osteoarthritis, sleep disorders, and multiple types of cancer. A weight loss of at least 5-10% can significantly improve health-related outcomes in obese patients. Phentermine, a low-cost agent approved in 1959, has become a commonly used weight-loss medication. This article explores the efficacy, safety, and optimal use of phentermine for weight loss, drawing on clinical studies and expert opinions.
The Obesity Pandemic and the Need for Therapeutic Options
Obesity rates are rising globally, with Mexico having the second-largest prevalence of obesity among adults worldwide, particularly affecting the low-income population. In Mexico, obesity in adults was 31% in 2012 and 33.6% in 2018. Projections estimate that by 2050, 54% of men and 37% of women in Mexico will be obese, leading to a doubling of obesity-related diseases. This upward trend is mainly attributed to increased consumption of convenience food and a more sedentary lifestyle.
While lifestyle interventions like diet and physical activity are essential, they often have poor adherence and low success rates. Pharmacotherapy is recommended as an adjuvant for patients with a BMI ≥ 30 kg/m2 or a BMI ≥ 27 kg/m2 with obesity-related diseases.
What is Phentermine?
Phentermine (phenyl-tertiary-butylamine) is a sympathomimetic amine that acts as an appetite suppressant. It stimulates the release of neurotransmitters in the brain, increasing levels of chemicals that make you feel full, thus reducing food intake. It is recommended in the short-term (12 weeks), alongside exercise, lifestyle modifications, and caloric restriction.
How Phentermine Works for Weight Loss
Phentermine helps reduce appetite, maintain eating habits, and boost energy. It reduces appetite, making it easier to make better food choices, eat smaller portions, and transition into a healthier lifestyle. Weight loss is a direct result of this reduced appetite. Lipid profiles also show improvement, especially in triglycerides as well as HDL cholesterol.
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Phentermine Dosage and Administration
Phentermine is taken orally. Until 2016, phentermine was only available in 3 doses of extended-release capsules - 15mg, 30mg, and 37.5mg. The 30 mg capsule or 37.5mg tablet is usually taken once a day in the morning, 1 to 2 hours before breakfast. The 8mg tablet can be taken up to 3 times daily, 30 minutes before a meal.
After ingestion, phentermine reaches peak concentrations in 3 to 4.4 hours. The drug’s half-life is about 25 hours.
Phentermine Weight Loss Results: Clinical Evidence
Mexican Study
A prospective, multi-center, open-label study evaluated the efficacy and safety of phentermine in 932 obese Mexican adults. Participants received 15 mg or 30 mg phentermine once daily for 6 months.
- Efficacy: 30 mg phentermine was more effective than 15 mg phentermine in improving anthropometric variables in the 3-month follow-up, but not after completing the 6-month treatment period.
- Non-responders: Nearly 40% of 3-month non-responders reached a body weight reduction of at least 5% at 6 months.
- Responders: Approximately 65% and 25% of 3-month responders maintained or improved their body weight reduction with long-term phentermine, respectively.
- Tolerance: Weight regain was approximately 10% from 3 to 6 months.
- Cardiovascular Risk: None of the doses increased cardiovascular risk, although mild-to-moderate adverse events were more frequent with 30 mg phentermine.
Korean Study
A randomized, double-blind, placebo-controlled study in Korea examined the effect of phentermine on weight reduction and safety in 68 relatively healthy obese adults. Participants received phentermine-HCl 37.5 mg or a placebo once daily with behavioral therapy for obesity.
- Weight Loss: The mean decrease in both body weight and waist circumference in phentermine-treated subjects was significantly greater than in the placebo group (weight: -6.7 ± 2.5 kg, p < 0.001; waist circumference: -6.2 ± 3.5 cm, p < 0.001).
- Significant Reduction: More subjects in the phentermine group achieved a weight reduction of 5% or greater from the baseline and 10% or more (p < 0.001).
- Adverse Events: Dry mouth and insomnia were the only statistically significant adverse events that occurred more frequently in the phentermine group.
US Study
A study using electronic health records from the Patient Outcomes Research to Advance Learning (PORTAL) cohort, including nearly 14,000 phentermine users, found evidence of better weight loss with longer-term use of phentermine (up to 2 years’ follow-up).
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- Longer-Term Use: Weight loss was clinically significantly greater among people who used the medication longer-term (more than a year) or medium-term (more than 112 days but less than a year) than in people who used it for only 3 months.
- Blood Pressure: Systolic blood pressure was reduced at 24 months in long-term users of phentermine relative to short-term users.
Phentermine Success Rate
95% of patients who use Phentermine experience positive results, with an average weight loss between 4-8 pounds per month. Approximately 10% of patients lose an estimated 10 pounds a month.
Factors Influencing Phentermine Weight Loss Results
Dosage
The Mexican study indicated that 30 mg phentermine was more effective than 15 mg phentermine after 3 months, but not after 6 months of treatment.
Duration of Treatment
The US study showed that longer-term use of phentermine (up to 2 years) resulted in better weight loss outcomes.
Lifestyle Modifications
Phentermine is most effective when combined with dietary changes, physical activity, and continuous medical supervision.
Potential Benefits of Phentermine
Significant Weight Loss
Studies have shown that phentermine can help you lose up to an average of 5% of your total body weight, with some studies showing weight loss of up to 10% over 12 weeks.
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Improvement of Health-Related Outcomes
A weight loss of at least 5-10% can significantly improve health-related outcomes in obese patients, including improvements in diabetes, high blood pressure, and cardiovascular diseases.
Reduction in Binge Eating Episodes
Studies have shown that obese or overweight people who suffer from BED or bulimia nervosa, and have been treated with phentermine, have lost not just weight, but also seen a reduction in binge eating episodes.
Phentermine Safety and Side Effects
Common Side Effects
The most frequent adverse events reported in studies include dry mouth, stress, increased appetite, pain in extremity, stretch marks, anxiety, constipation, back pain, polydipsia, and dizziness.
Cardiovascular Effects
Phentermine did not increase heart rate or blood pressure in the Mexican study. However, it is essential to monitor patients for any potential cardiovascular side effects.
Contraindications
Phentermine is not recommended for people with a history of heart problems (such as stroke, heart failure, uncontrolled hypertension, etc), people already taking stimulant medications (Adderrall, Vyvanse), patients with glaucoma, and patients with an over-active thyroid (hyperthyroidism).
Addiction Potential
When used properly for weight loss, Phentermine has a low potential for dependence. However, Phentermine is classified as a controlled substance, and every controlled substance has the potential for misuse. It is important to follow the dosing instructions provided by your healthcare provider.
Who Should Not Take Phentermine?
- People with a history of heart problems
- People already taking stimulant medications
- Patients with glaucoma
- Patients with an over-active thyroid
- Women who are either pregnant or breastfeeding
- People who have taken an MAO (Monoamine Oxidase) inhibitor in the last 14 days
Precautions and Monitoring
- It’s important to monitor patients for their response to phentermine treatment. About a third of people prescribed phentermine lost less than 3 percent of their weight within the first 3 months of starting the drug. These “non-responders” should not continue phentermine treatment, as they are unlikely to experience clinical benefit from it.
- The Nurse Practitioner will evaluate you during your visit to determine whether Phentermine is a good choice based on your medical history.
How to Get Started on Phentermine
To get started on Phentermine, come to Cordova Weight Loss for an office visit ($50). We are located at 1660 Bonnie Ln Suite 105 Cordova, TN 38016. No need to make an appointment; just come in during office hours. Your initial visit will be longer, due to paperwork and answering questions, but follow-up visits should usually be much quicker. Most visits are done within 30-35 minutes!