Best Supplements to Take with Phentermine

Prescription appetite suppressants are potent on their own, but when phentermine stops working adding a supplement is one way to promote continued weight loss. While some individuals receive approval from their doctors to take phentermine and supplements at the same time, most patients choose to experiment with supplements as they transition off the medication. 

Six of the most common weight loss supplements to take with phentermine, or for continued weight loss after treatment ends, are:

 Always ask your prescribing doctor and pharmacist before combining ANY additional medications or supplements with phentermine. A medical professional is the best person to assess the likelihood of possible drug interactions or negative side effects, especially given your individual medical condition and other prescription & OTC medications.


Melatonin sleepMany phentermine users are drawn to melatonin as a sleep aid if they struggle with phentermine-related insomnia. However, you should always ask your doctor before combining melatonin and phentermine given the substances’ opposite effects.

Purpose of Melatonin

Melatonin is a hormone that controls your sleep-wake cycles. It is made naturally in your brain’s pineal gland, but you can also take it as a dietary supplement. Melatonin supplements are available as pills, gummies or sub-lingual tabs. Available doses range from 1-10 milligrams [1]. 

This supplement is commonly used for adjusting sleep schedules. People take melatonin to cope with shift changes, jet lag, insomnia or other sleep disorders. Researchers are also still looking into other uses for this hormone. While it works very well for some users, others note little to no difference when using melatonin.

Even though melatonin is generally better-tolerated than other sleep aides, it is not harmless. Melatonin can cause daytime sleepiness, headaches, dizziness, stomach discomfort or mood changes (anxiety, depression or crankiness). It can also cause problems if you take it at the same time as other medications including blood thinners, immunosuppressants, diabetes medications or birth control pills [2].

Melatonin and Phentermine

The interaction between phentermine and melatonin remains undefined. Some sources warn that phentermine increases alertness, while melatonin dampens it. As a result, it is not advisable to mix them without a medical professional’s advice. However, some doctors do specifically prescribe melatonin to phentermine patients who struggle with insomnia. If you are interested in taking melatonin and phentermine together, bring it up to your doctor and pharmacist.

Capsicum / Cayenne Pepper

Capsicum / Cayenne Pepper boosts metabolismFood-based supplements have earned a certain fame in the past few years. One of the most popular, and most researched, food ingredient supplements is capsicum. It is a chemical derived from hot chili peppers and studies show it accelerates metabolism to promote weight loss.

Purpose of Capsicum

Capsicum helps suppress appetite, curb cravings and boost metabolism. Research shows that adding just a small amount of cayenne to food helps people eat less and resist cravings. These effects are especially strong if you don’t usually eat a lot of spicy food [7].

It also boosts metabolism to help you burn more calories – even at rest. Capsicum, like any spicy food, naturally increases core body temperature. Since your body likes to exist at a fairly exact temperature, your metabolism quickly revs to bring your core temperature back down to normal. Through this mechanism, capsicum boosts metabolism and promotes weight loss. In fact, subjects displayed higher resting energy expenditure even 4.5 hours after taking the capsicum supplement or eating cayenne pepper [7].

Can you take a fat burner while on phentermine?

Capsicum, in the form of cayenne pepper, is a popular ingredient in foods like curries, chili and seasonings. It is also common in fat-burning dietary supplements.

5 Star Fat BurnerThere is no listed drug interaction between phentermine and capsicum, however this does not mean than an interaction cannot occur. More, active ingredients in a fat burner (such as caffeine) may interact dangerously with phentermine or other weight loss pills. Capsicum could also interact with other drugs and medications, so ALWAYS consult with your doctor and pharmacist before taking any medication or supplement alongside phentermine. Many people find a fat burner useful to keep losing or maintain loss after transitioning off phentermine.

If your doctor and pharmacist approve of you taking capsicum supplements with phentermine, consider 5 Star Fat Burner. This supplement contains Capsimax® (cayenne pepper fruit extract) and GreenSelect® Phytosome® (green tea extract) as its two key components. These ingredients are clinically-proven to promote weight loss. Plus, 5 Star Fat Burner is naturally caffeine-free and formulated with five other supporting ingredients to encourage further weight loss.

 To read more about 5 Star Fat Burner or order now, click here.

Pre-Workout Supplements

Pre-workout supplementsExercise is critical to weight loss success, but some people feel like they lack the energy to power through a tough workout, even with the help of phentermine. Understandably, then, that many patients wonder about combining phentermine with pre-workout supplements to give their gym session an extra boost.

Purpose of Pre-Workout Supplements

Pre-workout supplements, commonly referred to as “pre-workout”, are powders that fitness enthusiasts take just before exercise to enhance performance. Different brands contain different ingredients, but popular ingredients include quick-digesting carbs, amino acids and B vitamins. Some products also contain caffeine or special ingredients like beet juice. These supplements claim to improve performance by boosting energy, and in some cases revving your metabolism or boosting your 'fight or flight' response. However, experts conclude that these products do not live up to their packaging claims in most cases [3]. 

Phentermine and Pre-Workout Supplement

It is best to steer clear of pre-workout supplements while taking phentermine.

Since phentermine already boosts energy by promoting a biological response similar to ‘fight or flight’, taking a pre-workout supplement is often just taking more of the same (and not in a good way). This combination could cause or exacerbate side effects like rapid heart rate or spikes in blood pressure. Since you don’t know how your body will react, and since every pre-workout supplement is different, taking phentermine and pre-workout together isn’t generally a good choice. This same logic is why healthcare providers ask you to minimize or avoid caffeine while taking phentermine.

Instead of Pre-Workout Supplements

Instead of risking the combination of phentermine and pre-workout, try these ideas to boost your energy before a big workout:

Vitamin B12

Vitamin B12Vitamin B12 and B vitamin complexes are popular supplements among phentermine users. In fact, weight loss doctors frequently prescribe B12 shots or pills with phentermine to boost patients’ energy and metabolism. Still, not all experts are convinced about this popular supplement’s true utility.

Purpose of B12 Supplements

B12 is a water-soluble vitamin found in most animal products, including eggs, fish, meat and dairy. This vitamin is critical for the amino acid conversion that allows for RNA, DNA, protein and lipid synthesis. It also supports proper neurological function and hemoglobin formation. While B12 deficiency remains relatively rare among healthy American adults, it is more common among older adults, vegans and people with gastrointestinal disorders [4].

As part of their standard slimdown program, many weight loss clinics offer B12 supplementation (either as a shot or a pill) to boost energy and metabolism. However, despite this common practice, one expert notes that extra B12 probably won’t help much for weight loss or energy unless you are deficient [5]. Still, if you are interested in B12 or other B vitamin supplementation, many doctors are willing prescribe this supplement to combat potential deficiency and aid weight loss.

Phentermine and Vitamin B12 Pills

Many phentermine patients take phentermine and B12 together, but almost always under the direct supervision of their doctor. While this vitamin is not likely to cause toxicity, it does interact with some medications. Always tell your prescribing doctor about all of your current & recent medications and supplements to minimize the risk of a negative drug interactions. If you are taking any medications for an acidy stomach, or metformin to manage diabetes, be sure to specifically discuss with your doctor how these pills interact with B12.

Conjugated Linoleic Acid (CLA)

Conjugated Linoleic Acid (CLA)After a couple months on phentermine, many people start looking for a way to boost their results – on the scale, in the gym and otherwise – and CLA remains a common choice. Patients report promising results with this supplement, but science is mixed. As with any other pill, always ask your doctor and pharmacist before combining any new medication or supplements with phentermine.

Purpose of CLA Supplements

Conjugated linoleic acid (CLA) supplements may help reduce body fat and weight when used in combination with regular physical activity. Scientific research is still mixed as to the effectiveness of this supplement, but many first-hand reports passionately support the use of CLA to reduce body fat. Studies are also mixed regarding the supplement’s possible negative effects with long-term use, namely related to worsening lipid profiles or glucose metabolism [6]. For this reason it is important to do your own research and assess whether CLA would prove beneficial for you in particular.

Phentermine and CLA

5 Star CLAThis supplement may help boost weight loss, especially fat loss, during your phentermine journey. Some users feel it is especially effective in increasing inches lost when used in combination with regular physical activity. Still, it is vital that your medical team remains aware of all medications and supplements in your daily routine. Check with your doctor and pharmacist before starting CLA.

If you and your medical team decide that CLA could benefit your weight loss journey, we recommend 5 Star CLA as one of the best brands on the market. This product contains CLA derived from safflower oil with a minimum concentration of 80%, the industry standard.

 To read more about 5 Star CLA or order now, click here.

5-Hydroxytryptophan (5-HTP) 

5-Hydroxytryptophan (5-HTP)5-HTP is one of the most common supplements for patients to take during or after their treatment with phentermine. This natural precursor to serotonin has been shown to increase satiety and boost weight loss on its own, but there is still no consensus as to whether it is safe or productive to combine it with phentermine.

Purpose of 5-HTP

5-hydroxytryptophan, or 5-HTP, is a precursor to serotonin. This essential neurotransmitter helps to control sleep, mood, and hunger, so inadequate serotonin can have a significant effect on health and well-being. 5-HTP supplements are made from either the seeds of the African tree called Griffonia, or synthetically produced in chemical laboratories. 

Most people consume adequate 5-HTP in their diets as long as they eat enough protein. However, stress, poor diet or lack of exercise our modern lifestyles can result in low levels of serotonin. If low levels of 5-HTP have been identified as a possible cause, a doctor may recommend 5-HTP supplements.

5-HTP promotes weight loss by serving as a precursor to serotonin that:

5-HTP And Phentermine

One observational study on combination pharmacotherapy for weight loss stated that, “Combining 5-HTP and phentermine generally results in greater weight loss than would be observed with either medication alone.” He also noted that patients experience fewer stimulant side effects when phentermine and 5-HTP are administered at the same time. However, doctors agree that controlled trials should be conducted before medical professionals adopt a widespread acceptance of this combination [12]. 

Like any other supplement, always consult with your doctor and pharmacist before combining 5-HTP and phentermine. A medical professional can help you navigate how much 5 HTP to take with phentermine and when to take 5 HTP (time of day) with phentermine.


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2. WebMD Staff. (2017). What Is Melatonin?  Retrieved from WebMD:

3. Fetters, K. A. (2017, Nov 12). What Are Pre-Workout Supplements — and Do You Need Them? Retrieved from

4. Office of Dietary Supplements. (2018). Vitamin B12. Retrieved from National Institutes of Health: Office of Dietary Supplements:

5. Bauer, D. B. (2018). Are vitamin B-12 injections helpful for weight loss?  Retrieved from Mayo Clinic:

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10. Shell, W., Bullias, D., Charuvastra, E., May, L. A., & Silver, D. S. (2010). A Randomized, Placebo-Controlled Trial of an Amino Acid Preparation on Timing and Quality of Sleep. American Journal of Therapeutics, 17(2), 133-139. doi:10.1097/mjt.0b013e31819e9eab

11. Shaw, K. A., Turner, J., & Mar, C. D. (2002). Tryptophan and 5-Hydroxytryptophan for depression. Cochrane Database of Systematic Reviews. doi:10.1002/14651858.cd003198

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