Phentermine is an FDA-approved appetite suppressant that has been on the market since 1958. For more than 60 years, it has been the most commonly prescribed weight-loss medication worldwide.
Phentermine is a sympathomimetic medication, meaning it works similarly to certain medications used to treat ADD or ADHD. It acts on the hypothalamus, the part of the brain that regulates hunger, to reduce appetite. Through its mild stimulant effects, it also helps increase metabolism.
Because of its stimulant-like properties, some patients report feeling more energized or “speedy” when first starting Phentermine. This sensation typically resolves within the first few weeks as the body adjusts.
When prescribed and used correctly, Phentermine is safe, effective, and inexpensive.
Typical Dosing
Phentermine is usually started at ½ of a 37.5 mg tablet (the pill is scored). The dose may be increased to a full tablet daily if appetite suppression becomes less effective or if the patient is ready for a higher dose.
How Is Phentermine Taken?
For best absorption and effectiveness, Phentermine should be taken on an empty stomach, ideally first thing in the morning upon waking.
Patients should wait at least one hour before eating. During that time, water, coffee, or any zero-calorie beverage is allowed.
Once a patient becomes accustomed to the medication, it can be taken slightly later in the morning. This can help extend its appetite-suppressing effects into the evening and reduce nighttime hunger and cravings.
How Long Can Phentermine Be Taken?
One of the most common questions patients ask is how long Phentermine can be used.
As long as there are no contraindications or significant side effects, Phentermine can be taken as long as needed to achieve and maintain a patient’s weight-loss goals.
Phentermine is also a valuable maintenance medication. By decreasing hunger and increasing metabolism, it helps counteract the body’s natural tendency to regain weight and return to its “set point.”
Obesity is a chronic disease, and treatment does not end once a goal weight is reached. Just as blood-pressure medication is continued after blood pressure improves, weight-loss medication should often be continued during maintenance.
What Are the Side Effects?
Most patients tolerate Phentermine well. The most common side effects include:
- Dry mouth – This often encourages increased water intake, which is beneficial for weight loss.
- Mild constipation – Staying well hydrated usually prevents this. If needed, over-the-counter options such as Miralax or Milk of Magnesia can be used temporarily.
- Blood pressure changes – All stimulant medications can increase blood pressure. Patients already on blood-pressure medication should monitor their readings. In practice, blood pressure often improves as weight is lost.
- Sleep disturbance – Taking Phentermine too late in the day may interfere with sleep.
On a positive note, patients with previously undiagnosed ADD often report improved focus and productivity while taking Phentermine.
Who Should Not Take Phentermine?
Phentermine is not appropriate for everyone. It should not be used by patients with:
- Severe heart disease
- Untreated arrhythmias or structural heart abnormalities
- History of stroke or severe peripheral vascular disease
- Acute angle-closure glaucoma
- Bipolar disorder with mania
A full medical evaluation is essential before starting treatment.
In Summary
Phentermine is an FDA-approved appetite suppressant that helps patients lose weight and maintain long-term weight loss. It works by reducing hunger and increasing metabolism, making it especially helpful for patients with a slower metabolic rate.
When taken on an empty stomach and paired with adequate hydration, Phentermine is safe, non-addictive, and cost-effective. It does not act on dopamine receptors, meaning it can be started or stopped safely under medical supervision.
For patients without contraindications, Phentermine remains an excellent and proven option in medical weight-loss treatment.