With so many new medications in the weight loss world, it can be hard to keep up! Is phentermine (the most commonly prescribed diet pill in the world) still relevant with the rise of weight loss injectables like Ozempic? Let’s start with a deep dive into phentermine, which remains today, my favorite anti-obesity medication (AOM). Then let’s take a look at how things have changed with the rise of other new drugs and how they can actually be used alongside phentermine for optimal weight loss results.
What is Phentermine?
Phentermine is an FDA-approved appetite suppressant pill that has been on the market since 1959. Being a sympathomimetic, it is similar in character to the drugs that are used today to treat ADD or ADHD. It works at the level of the hypothalamus to decrease hunger and through its stimulatory effects, increases metabolism.
Because it is similar in structure to stimulants, some patients may experience a “speedy” or “energized” feeling when they first start taking phentermine. This resolves once your body becomes used to the medication, which is typically within the first few weeks of use.
How is Phentermine Dosed?
When starting phentermine 37.5 mg (the dose used in our office), you should always start with a half pill. It is scored and easily “split-able” by hand or you can use a pill splitter. You may increase the dose to one whole pill daily if you begin to feel like the medication is not suppressing your appetite all day.
If you cannot tolerate half of the 37.5 mg pill (18.75mg), there is an even lower dose available under the brand name Lomaira. A full tab of Lomaira has 8 mg of phentermine. For my very sensitive patients, I will start them on a half tab of Lomaira which is 4 mg. This dose is well tolerated by just about everyone, and can be slowly titrated upward, half a pill at a time.
How is Phentermine Taken?
Phentermine is an oral pill that should be taken on an empty stomach so that it can be absorbed properly and work most effectively. It is highly recommended that you take phentermine immediately upon waking up so that it doesn’t affect your sleep. You should wait at least one hour after taking the medication to eat. Drinking water or black coffee during this one hour after taking the medication is fine.
If you tend to skip breakfast or eat a very light breakfast, it’s okay to take your pill later in the morning around 10 or 11 am, as long as your stomach is not full. If you fall asleep easily and are a sound sleeper, this is a good choice as it will last later into the evening and prevent late-night hunger and cravings.
Side Effects of Phentermine
Dehydration
Phentermine can dehydrate you and it is common to experience a dry mouth. Make sure to drink plenty of water when taking this medication, which should be on average 60-100 ounces per day.
Constipation
Some patients will experience mild constipation. Again, keeping your fluid intake high can prevent this. If you are reaching your water goals and still struggling, you can take two tablespoons of milk of magnesia morning and night until the constipation subsides. Another option is to use polyethylene glycol powder (Miralax). Dissolve 17 grams in eight ounces of water or another beverage daily until the constipation subsides.
High Blood Pressure
All stimulants can potentially raise your blood pressure. If this happens, it is generally mild, and tends to occur within the first hour or two and then steadily drops back to normal. If you take medication for high blood pressure, keep a blood pressure journal. Check your blood pressure two hours or more after taking the phentermine for an accurate reading. This will help your provider know how your blood pressure is doing on a daily basis. If you don’t own a blood pressure cuff, you can check it at just about any pharmacy. When your weight significantly drops, expect your blood pressure to come down also. This may require taking you off your blood pressure medication—another important reason to monitor it regularly.
Who Should Not Take Phentermine?
Some people should not take phentermine. Providers will carefully screen your medical history and list of medications before prescribing to make sure it’s safe.
Do not take this medication if you have:
- Severe heart disease (when recommended by a cardiologist to avoid)
- A history of abnormal heart rhythm (when recommended by a cardiologist to avoid)
- Structural abnormalities of the heart (as recommended by a cardiologist)
- Had a hemorrhagic stroke
- Peripheral vascular disease
- Acute angle closure glaucoma
- A seizure disorder (as recommended by a neurologist)
- Bipolar depression (it can precipitate mania)
Phentermine and Weight Loss Injectables
Phentermine can work alongside or as a replacement for weight loss injectables. It is the only AOM that increases metabolism and decreases hunger, which is extremely beneficial for patients who are hypometabolic (having a low metabolic rate). Injectables work by targeting the GLP-1 receptor in our brain and gut, and delays gastric emptying which reduces appetite and promotes fullness.
Comparing Cost and Accessibility
Phentermine is readily available and inexpensive. At our office, we dispense it free of cost to our patients and have not had any supply chain issues thus far. With injectables, insurance coverage is a moving target, and availability is often limited, leaving patients in a lurch when they can’t get their prescription filled.
As I speak to my colleagues in our field, it seems that many of us are using both injectables and phentermine for the weight loss piece, but switching over to just phentermine for maintenance when possible (due to the unpredictable cycle of availability and coverage for injectables), Additionally, phentermine can be used if a dose is unavailable to help continue the weight loss process.
Comparing Safety
Phentermine is easily titrated and non-addicting (you can start and stop with no complications). With injectables, there are many side effects and dosing has to be carefully titrated up and down.
Comparing Weight Loss Results
Weight loss-wise, we have seen over 10% weight loss pretty regularly compared to placebo. When paired with a GLP-1 (injectable) for the weight loss phase, it is extremely high, reaching 15-20% or more depending on drug and dose.
Is Phentermine Still Prescribed Regularly?
Obesity Medicine Physicians (experts in the field of weight loss) still prescribe phentermine regularly. Injectables have been available for far longer than the media hype surrounding them. Many of us see the mess that has been created around these medications and use them with caution. However, we recognize that they are a powerful tool in our tool chest when used properly.
Phentermine’s Lasting Impact
Phentermine remains relevant as a reliable drug that has been studied for long-term use. It has been proven time and time again to be a safe and effective treatment to manage obesity and maintain long-term weight loss.
