Phentermine: indications, dosages, and side effectsPhentermine is an anorectic—a drug that suppresses hunger for short-term weight loss. Read our article to learn about phentermine therapy, availability, and side effects of the drug.

Phentermine: a comprehensive guide

Phentermine is a drug that suppresses hunger—they are also called anorectic. It was FDA-approved in the USA in 1959. Chemically, it is an amphetamine derivative—α-methyl-amphetamine. The drug is a Schedule IV controlled substance and cannot be legally obtained in the USA unless prescribed by a licensed medical professional. The patient can receive no more than 5 refills during 6 months. Phentermine is manufactured under various names, such as:

• Adipex-P;
• Sentis;
• Suprenza;
• Ionamin;
• Metermine.

How it works

Like other amphetamines, phentermine stimulates the CNS. It is not fully established how exactly the drug affects appetite. Allegedly, the compound can boost the levels of dopamine, serotonin, and norepinephrine in the brain, changing how the person feels and behaves. Additionally, higher norepinephrine outside the brain can promote faster fat burning.

How is phentermine used

Phentermine is indicated for short-term treatment of exogenous obesity. Exogenous means that the patient is overweight because of excess calorie intake (being sedentary and overeating). The standard protocol is to combine treatment with healthy lifestyle changes, including physical activity, changing behavioral patterns, and monitoring diet. The drug is typically prescribed to patients who have a body mass index (BMI) of 30 kg/m² and higher. If there are other health risk factors, such as diabetes or hypertension, present, the threshold is lowered to a BMI of 27 kg/m² to prevent further damage to the patient’s health. Phentermine is produced in capsules, pills, or tablets, of 15 mg, 30 mg, or 37.5 mg strength. There are also ODT tablets that dissolve on the tongue and release the medication faster. Being a CNS stimulant, the drug can cause insomnia. Therefore, it is best to be taken in the morning. Food does not affect its absorption—patients can take it with or without meals. The dosage has to be determined by the medical professional depending on how the patient reacts to treatment. The goal is to find the lowest effective dose.

Abuse, dependence, and other risks

When a doctor tries to help their patient lose weight and considers prescribing phentermine, they should remember that the drug has a high potential for abuse and dependence. These risks are the reason why the drug cannot be used by people who have a history of such issues. There are studies claiming that phentermine therapy did not lead to such consequences in patients. However, their pool of participants is limited and more research is needed to state that the drug is safe in that regard. If a patient develops tolerance to phentermine (when the body sort of “gets used” to the drug and does not respond to it properly), the treatment is to be discontinued. Phentermine usage, either alone or in combination with other medications, has been linked to the development of PPH (primary pulmonary hypertension) and cardiac valvular disease in patients who were otherwise healthy. There is also a case report of cardiomyopathy induced by the drug in a patient who did not have significant history of cardiac issues.

Side effects

The reported adverse reactions to phentermine affect various body systems.

Cardiovascular system

• heart palpitations—a sensation that the heart flutters, beats too fast, or pounds heavily;
• ischemization—decreased blood supply that affects organs and tissues negatively;
• hypertension—elevated blood pressure;
• tachycardia—increased heart rate.

CNS

• dizziness;
• restlessness;
• insomnia;
• impaired ability to focus;
• overstimulation;
• euphoria or dysphoria;
• headache;
• psychosis;
• tremor.

Other

• mouth dryness;
• hives;
• erectile dysfunction;
• changes in libido;
• diarrhea;
• constipation, etc.

Who cannot use phentermine

The medication is contraindicated to patients who:

• are pregnant or nursing;
• have a history of cardiovascular diseases;
• have hyperthyroidism (when the thyroid gland produces too much hormones);
• have glaucoma (a condition associated with increased pressure inside the eye that damages the optic nerve and impairs vision);
• are prone to agitated states;
• have a history of drug abuse;
• are hypersensitive or intolerant to sympathomimetic amines.