Diethylpropion vs Phentermine: Two Weight Loss Drugs Compared

If you're exploring prescription options for weight loss, you may come across diethylpropion and phentermine. These medications have been used for decades to support short-term weight management, especially when combined with nutrition, activity, and behavior changes. But figuring out which one is right for you can feel overwhelming. This guide breaks down everything you need to know about diethylpropion vs phentermine, including how they work, possible side effects, and safety considerations.

What Is Phentermine?

Phentermine is a prescription medication used for short-term weight loss. It belongs to a class of drugs called sympathomimetic amines, which stimulate your central nervous system to reduce your appetite. It contains the active ingredient phentermine hydrochloride. In many cases, healthcare professionals prescribe phentermine for people with a body mass index (BMI) of 30 or above, or 27 and above with certain health conditions like high blood pressure, high cholesterol, or type 2 diabetes. You may see phentermine compared with similar medications in searches like Tenuate vs phentermine, Bontril vs phentermine, or phentermine vs diethylpropion. These comparisons usually reflect different brand names or closely related appetite suppressants. Phentermine is available in several doses and formulations. Sold under brand names such as Adipex-P® and Lomaira®. Because Adipex is so widely recognized, patients often search for Tenuate vs Adipex to understand the differences between these two common appetite-suppressing medications.

How Does Phentermine Work?

Phentermine works by stimulating your central nervous system and increasing certain brain chemicals involved in appetite control. This helps you feel less hungry and may make it easier to eat smaller portions. It can also increase alertness, which is why some people notice stimulant-related side effects.

What Is Diethylpropion?

Diethylpropion is another prescription appetite suppressant that has been used since the 1950s. It works similarly to phentermine by stimulating your central nervous system to help decrease appetite. While phentermine is often the go-to for many providers, diethylpropion is a frequent alternative. It is commonly known by brand names like Tenuate® and Tenuate Dospan®, and internationally as anfepramona. When researching weight-loss options, you may see comparisons such as phentermine vs. Tenuate or phentermine vs. Bontril. It is important to note that Bontril (phendimetrazine) is a different stimulant medication that is also used for short-term weight management. Diethylpropion is available in immediate-release tablets and extended-release formulations, which often leads to searches such as diethylpropion 75 mg vs phentermine as patients compare dosage strengths and effectiveness.

How Does Diethylpropion Work?

Diethylpropion reduces appetite by stimulating the central nervous system, similar to phentermine, but it is generally considered milder. Immediate-release tablets act quickly and wear off sooner, while extended-release forms provide steadier appetite control throughout the day.

Why Use Diethylpropion vs Phentermine for Weight Loss?

Both medications can support weight loss by helping reduce appetite, which may make it easier to follow a lower-calorie eating plan. However, you might prefer one over the other depending on how your body responds and on your healthcare professional's recommendations. When weighing the pros and cons of phentermine and diethylpropion, factors that often guide your choice include:

• Your healthcare provider’s recommendation based on your overall health
• Your medical history, especially any heart or blood pressure concerns
• How well you handle stimulant-related side effects
• Whether specific doses or extended-release options are available to you
• Your experience with weight-loss medications
• Cost, pharmacy pricing, and insurance coverage

Although both medications have been used for decades, they don't affect everyone the same way.

What Is the Difference Between Phentermine and Diethylpropion?

Phentermine and diethylpropion are both stimulants, but they vary in strength, release options, and how long they stay active in your body. Phentermine is generally considered stronger, while diethylpropion is often described as milder. These differences can influence which one feels more comfortable or effective for you.

Phentermine vs Diethylpropion: Comparison Table

Below is a side-by-side comparison to help you understand how they differ.

Feature	Phentermine (e.g., Adipex-P)	Diethylpropion(e.g., Tenuate)
How it works (Mechanism)	Stronger sympathomimetic amine; it primarily works by releasing norepinephrine in the brain to reduce appetite.	Milder sympathomimetic amine; also works by increasing norepinephrine/dopamine, but generally with less central nervous system activity.
Formulations	Immediate-release (IR) and Extended-release (ER) tablets and capsules (e.g., 8 mg, 15 mg, 30 mg, 37.5 mg).	Immediate-release (IR) tablets (25 mg) and Controlled/Extended-release (CR/ER) tablets (75 mg).
Dosing	Most common: Once daily (15 mg to 37.5 mg). Lower dose (8 mg): Up to three times daily before meals.	IR (25 mg): Three times a day, one hour before meals. ER (75 mg): Once daily in mid-morning.
Strength of Effect	Generally, stronger appetite suppression and associated with greater average weight loss in studies.	Milder appetite suppression; may be easier to tolerate for those sensitive to strong stimulants.
Common Side Effects	Dry mouth, insomnia, restlessness, increased heart rate/blood pressure, irritability.	Dry mouth, mild dizziness, headache, stomach upset, and less pronounced cardiac/sleep side effects than phentermine.
Typical Use	Indicated for short-term use (up to 12 weeks). Part of a comprehensive lifestyle plan.	Indicated for short-term use (up to 12 weeks). Sometimes preferred for its milder profile.
Controlled Substance Class	Schedule IV (indicates lower potential for abuse than Schedule II-III medications, but monitoring is still required).	Schedule IV (indicates lower potential for abuse than Schedule II-III medications, but monitoring is still required).

Why the 12-week limit? The FDA approves these medications for short-term use. Typically, up to 12 weeks, because their effectiveness may decrease over time as your body adapts, and long-term safety data remains limited. Your healthcare provider can help determine which dosing schedule fits best with your lifestyle and preferences.

Is Phentermine the Same as Diethylpropion?

No. Both are stimulant-like medicines that help curb hunger for weight loss, but they're different drugs with their own chemical makeup. In one study of adults who were significantly overweight (more than 20% above healthy weight ranges), researchers compared phentermine 30 mg once daily with diethylpropion 75 mg once daily, both with a 1,500-calorie diet. Over 12 weeks, phentermine helped people lose more weight, especially in the final month, though both drugs worked well and were mostly easy to tolerate. Phentermine generally provides stronger appetite suppression and longer-lasting effects for most people. Diethylpropion is usually gentler and is available as either quick-acting 25 mg tablets or longer-lasting 75 mg tablets. When patients search for Tenuate vs phentermine or phentermine vs bontril, they are typically looking for this balance between potency and side-effect tolerance.

Is Diethylpropion as Good as Phentermine?

Yes, for many people it works great. Studies show both drugs help with short-term weight loss when paired with healthier eating and increased activity. Diethylpropion users lost slightly less weight than phentermine users over 12 weeks, but the difference was still clinically meaningful. At six months, people on diethylpropion lost nearly 10% of their starting weight (vs. just 3% on placebo), and they kept most of it off at one year. The best choice boils down to: how stimulants affect you, your health background, any side effects, and what your healthcare provider recommends. Diethylpropion is effective (even if sometimes slightly less potent than phentermine), and its milder effects make it a preferred choice for people who want good appetite control without as much stimulant intensity.

What Side Effects Are Common Between Diethylpropion and Phentermine?

Both medications share many of the same stimulant-related side effects because they affect your nervous system in similar ways. Common side effects may include:

• Dry mouth
• Increased heart rate
• Insomnia
• Constipation
• Increased blood pressure
• Nervousness or restlessness
• Headache

Your healthcare professional may monitor your blood pressure and overall cardiovascular health while you take either drug.

What Side Effects Are Not Common Between Diethylpropion and Phentermine?

While their shared stimulant effects overlap, each drug has some unique considerations:

Phentermine:

• May cause more noticeable insomnia
• May cause bigger increases in heart rate
• May interact with more medications due to its stimulant strength

Diethylpropion:

• May cause dizziness in some people
• Extended-release versions may cause mild stomach upset
• Immediate-release forms may lead to mid-day wear-off feelings

These differences may help you and your healthcare professional decide which option is the better fit.

How Successful Is Phentermine in Treating Obesity?

Studies show that phentermine can help with weight loss when it’s used for a short time along with healthy eating and activity changes. In a 24-week clinical study, people who took phentermine (15 mg per day) as part of a structured weight-loss program lost about 6% of their body weight, compared with about 3% in people who followed the program without the medication. In that same study, just over half of those taking phentermine lost at least 5% of their starting weight, while only one in four in the placebo group reached that level. This shows that phentermine can be a helpful short-term option for people who haven’t had enough success with lifestyle changes alone.

How Successful Is Diethylpropion in Treating Obesity?

Diethylpropion has been used for decades and is supported by clinical data showing effective short-term weight reduction. Research demonstrates that people taking diethylpropion lose significantly more weight compared to those taking a placebo. In clinical trials, diethylpropion users achieved an average placebo-subtracted weight loss of 6.6% over 6 months, with over two-thirds (67.6%) reaching the 5% weight-loss milestone. When considering dosing convenience, many patients compare diethylpropion 75 mg vs phentermine. While both medications belong to the same class of sympathomimetic amines, diethylpropion is often noted for its consistent safety profile in long-term studies, despite its typical short-term indication.

Is Phentermine Better Than Diethylpropion for Weight Loss?

Not always. Phentermine may suppress appetite more strongly, but diethylpropion may be a better choice if you want a gentler option. Effectiveness varies from person to person. Both medications require close monitoring and should always be used under the care of a healthcare professional.

Related FAQs

 

Can you take phentermine and diethylpropion together?

You should not take these medications together. Both are stimulants, and combining them increases the risk of side effects such as high blood pressure, irregular heart rhythms, anxiety, and insomnia. Your healthcare professional will recommend only one medication at a time for safety. Together, these medications can overstimulate your nervous system. If you feel your current prescription isn't working well enough, speak with your healthcare professional before making any changes.

Does phentermine suppress your appetite?

Yes, phentermine suppresses appetite by stimulating your central nervous system. This helps you feel less hungry and may make it easier to follow a reduced-calorie eating plan. Phentermine increases neurotransmitters, such as norepinephrine, which play a role in satiety. This effect helps many people feel more in control of their eating patterns, especially early in their weight-loss journey.

Does diethylpropion suppress your appetite?

Yes. Diethylpropion works similarly to phentermine by reducing appetite through central nervous system stimulation. Many people experience mild to moderate appetite suppression, which can support weight loss when combined with changes in nutrition and activity. Although diethylpropion may be gentler than phentermine, it can still help you manage hunger cues effectively. Some people prefer it because it may cause fewer stimulant-related side effects.

Diethylpropion vs phentermine: Which has more risks?

Phentermine generally carries more stimulant-related risks, such as increased heart rate, elevated blood pressure, and insomnia. Diethylpropion also carries risks, but many people find it milder. The safer option depends on your health history and how you respond to stimulants. Your healthcare professional will help you choose the medication that best balances benefits and risks for your situation. Be sure to discuss any heart-related concerns, sleep issues, or medication interactions when considering these treatment options.

How ScriptSave® WellRx Can Help You Save on Prescriptions

If you and your prescriber decide that one of these medicines is right for you, the next question is often, How much is this going to cost? Prices can vary widely from pharmacy to pharmacy, even within the same zip code. ScriptSave® WellRx can help you compare prices and find discounts of up to 80%* off the cash price on many prescriptions, including medicines like phentermine or diethylpropion, depending on your location and pharmacy. Our program isn't insurance. It's a way to increase transparency into prescription costs so you can keep more of your money in your pocket. You can search your medication, dosage, and zip code at WellRx.com to see prices at nearby pharmacies and find where your prescription may be most affordable. DISCOUNT ONLY – NOT INSURANCE. Medical Security Card Company, LLC, administers the program.\

 

Bio: Alyse Thompson, M.D., is a freelance medical writer with experience caring for patients in primary and urgent care settings. She also has a master's degree in basic medical science. She has managed acute and chronic diseases and participated in medical and pharmaceutical research.

References

https://www.nhlbi.nih.gov/health/overweight-and-obesity

https://www.wellrx.com/adipex-p/drug-information/

https://www.wellrx.com/diethylpropion-hcl/drug-information/

https://www.wellrx.com/lomaira/drug-information/

https://www.nature.com/articles/s41591-025-03556-3

https://reference.medscape.com/drug/adipex-p-lomaira-phentermine-343002

https://reference.medscape.com/drug/diethylpropion-cr-343077

https://pubmed.ncbi.nlm.nih.gov/6844367/

https://pubmed.ncbi.nlm.nih.gov/19564877/