Can Phentermine cause headaches?

by Rakib Sarwar, RPh
Published on March 6, 2019 and last updated for accuracy on September 19, 2022
woman suffering from headache and holding her head

With so many people battling with overweight and obesity-related problems, new weight loss drugs cannot stop hitting the market anytime soon. With several new weight loss drugs being advertised by different companies, one needs to be careful when choosing. You don’t want to spend your hard-earned money on drugs that can neither help you lose weight nor maintain your normal health.

The worldwide popularity of phentermine may be related to its effectiveness for weight loss. In this post, we will help you learn about phentermine, who can take it, side effects to watch out for, and phentermine may cause headaches (1).

What is phentermine?

Phentermine is an over-the-counter drug for weight loss. It can come in different forms such as an oral capsule, orally disintegrating tablet, or an oral tablet. Phentermine capsule comes as the Adipex-P drug brand. It can also come in the form of a generic drug.

All generic drugs are known to be more affordable than their branded counterparts. In most cases, these generic versions may not come with the strength and form the branded ones come in. Since phentermine is a form of controlled substance, it is important you ensure the close monitoring of a doctor while you are on this drug (6).

Potential risks of phentermine use

The oral capsule form of phentermine is administered for some weeks as a treatment for obesity. This is one drug that has been found to help obese and overweight people lose weight. However, it comes with some known health risk issues (2).

Some common risk factors associated with the use of phentermine include high cholesterol, high blood pressure, and diabetes. Phentermine is used alongside weight loss exercises, a low-calorie diet plan, and some behavioral changes aimed at enhancing your weight loss (5).

How phentermine may help you lose weight

Phentermine is a member of the anorectics drug class. A drug class is made up of a group of medications formulated to work in the same way. Drugs belonging in the same class are used for the treatment of similar cases (2).

It is believed that phentermine helps you lose weight by enhancing the production of important brain chemicals that help curb your appetite. The release of these brain chemicals can help curb your food cravings, thereby aiding your weight loss faster (3).

Phentermine and headaches – a common complaint

Headaches (including migraines) are among the most commonly experienced side effects while on phentermine. These headaches can range from mild to severe (4).

These headaches may or may not be related to the phentermine pills. The lifestyle changes you initiate while on phentermine can account for the recurrent headaches you experience. Whether these headaches are mild or severe, they are known to affect your overall comfort and quality of life.

Below, we will help you learn the most possible causes of a headache while on phentermine and how you can overcome this side effect. Most times these headaches would go away on their own, but if they persist, you may have to consult a physician as they may be a sign of an underlying serious ailment (4).

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So who can get these headaches while taking phentermine?

Despite the fact that headache is a common side effect with phentermine, not everyone will experience it while taking phentermine. The people most prone to developing headaches while on phentermine are new users. Using phentermine alongside other drugs can also increase your chances of developing headaches with the drug (8). So, let’s see who stands a higher risk of developing headaches while on phentermine:

New Users

You stand a higher risk of developing headaches with phentermine as a new user. This is also applicable to most other common side effects that accompany the use of this weight loss drug (8).

The reason for this increased risk of developing headaches as a new user is related to the fact that your body needs some time before it can get used to the drug and its effects on your body (7).

Some people are known to be more sensitive to chemical substances than others. So, if you are among the overly sensitive type, you will most likely react more to phentermine and experience more of these headaches than most other new users would. These headaches are part of your body’s way of adjusting to the new drug and its effects (8).

However, if this headache persists for more than a few days or weeks, you may need to get in touch with your doctor to help diagnose any underlying ailment. Where there is no underlying ailment, your doctor may decide to change your phentermine dosage or change the schedule to help you experience fewer side effects (4).

Most times, it is not about taking a high dose of the drug as phentermine still produces the needed weight loss effects even at a lower dosage. However, make sure you never change your schedule or dosage without speaking with a doctor first (7).

Smokers and drinkers

One other major factor that increases your risk of developing headaches with phentermine is your lifestyle changes and choices while on phentermine. The drug interaction between phentermine and chemical substances is one reason why you would experience more headaches while drinking, smoking or taking caffeine alongside phentermine. This is why it is advised you avoid taking these substances while on phentermine (9).

It is advised you never combine alcohol and phentermine as it can be one dangerous combination that can usher in loads of side effects. The interaction of alcohol with phentermine is known to increase stress, dizziness, and sleepiness in your body. This interaction can also increase your blood pressure. So, make sure you skip alcohol whenever you are on phentermine to curb these side effects (10).

Also, nicotine and caffeine are two other intoxicating substances you may wish to never combine with phentermine. These are stimulants and can lead to higher risks of side effects with phentermine. A severe headache is a common side effect that occurs when you combine phentermine with any of these stimulants (10).

So what are some possible causes of headaches while on phentermine?

There are several possible causes of headaches with phentermine just like we have mentioned earlier. Sometimes, it is difficult to identify the real cause of each an individual headache while taking phentermine.

Therefore, knowing the possible causes of headaches while on phentermine will go a long way to help you identify the major cause you should deal with at any particular time. Below are some common possible causes of headaches while on phentermine. Some of these causes may be related to the drug itself or some lifestyle changes that accompany the drug intake.

1. Taking additional stimulant drugs or supplements

The stimulant effects have been identified as one major possible cause of headaches while on phentermine. Phentermine creates certain effects in your body that can be likened to the adrenaline rush termed the “flight or fight” response. One major effect of this adrenaline rush-like response is the narrowing and tightening of your blood vessels in your body’s digestive organs. Another effect this response can have in your body is the widening of the blood vessels in your brain, lungs, heart, and skeletal muscles (9).

Most of these chemical changes that come with this type of stimulated stress response can increase your heartbeat. And this increased heartbeat supplies the needed nutrients and oxygen to your body. This is why most phentermine takers would always report an increase in their heart rate and blood pressure while on the drug. These cardio changes are the major reasons why taking phentermine with a history of high blood pressure or any heart diseases is considered dangerous (9).

The synthesized stress response initiated by the dilation of the cerebral arteries increases the flow of blood to your brain. While this may not cause any brain pains, the expansion of your blood vessels can trigger the surrounding nerves which send pain signals to your face and head. These pain signals may be the major reasons why you experience headaches with phentermine (9).

If you experience persistent headaches with a high dose of phentermine, you may wish to ensure you speak with your doctor to reduce your dosage and change your schedule.

2. Dehydration

Dehydration is one other major cause of headaches with phentermine. Most doctors will advise you to take plenty of water while taking phentermine. Staying adequately hydrated will help you keep your kidneys protected, control your food cravings, and nourish your skins. It will also help you control the common side of effect of phentermine known as xerostomia or dry mouth. While this xerostomia may not be caused by dehydration, not taking enough water can worsen the condition (9, 11).

It is easy to become dehydrated when you forget to take enough fluids. It is a known fact that not taking enough water can give you headaches even when you are not on phentermine. Being dehydrated will make your blood vessels to contract, keep your electrolytes unbalanced, and these two effects of dehydration can lead to severe pain signals in your brain (9, 11).

So, taking adequate fluids is one way you can treat this type of headache. Make sure you consume enough water to keep your body tissues adequately hydrated. Taking 2-3 glasses of water when you experience a sudden headache will help you keep the headache at bay. If your headache is caused by dehydration, it should go away from 30 minutes to 3 hours (9, 11).

Never forget you stand the risk of becoming more dehydrated with alcoholic and caffeinated beverages. The best drinks to help you stay hydrated are sugar-free, caffeine-free drinks (11).

3. Skipping Meals

Skipping meals is one other major reason why you will likely develop headache with phentermine. Not eating enough food can also make you develop a headache while on phentermine. Following a highly restrictive diet can also leave you with headaches due to the low blood sugar associated with such restrictive diets (9, 11).

Your body cells make use of glucose known as blood sugar for energy. Among your body cells, your body neurons consume most of the glucose. So, to ensure your brain keeps functioning at a high peak, make sure you control your body’s glucose supply. This explains why any drop in your body’s blood sugar gives you headaches. Once you develop low blood sugar or hypoglycemia, you can have headaches, nausea, confusion, or any other symptoms. If you have diabetes, fast for long, or eat foods high in sugar, you will experience more glucose deficiency-related headaches (9, 11).

Your body will also release stress hormones whenever you fast, and these stress hormones can worsen your headaches when on phentermine. To keep your hypoglycemic headaches away, eat once in every 4-6 hours. If you have a problem controlling your blood sugar or any diabetes-related complications, you can settle for meals or snacks every 3-4 hours while you are awake (10, 11).

If you are too busy to eat regularly, make sure you complement with a good meal replacement shake or some healthy snack. You can limit your calorie intake to about 1200 each day as a woman or 1500 a day as a man while on phentermine (10, 11). This will help regulate and maintain important healthy bodily functions. Additionally, taking adequate meals while on any drugs helps the drug function more effectively.

4. Inadequate Sleep

Last but not the least on the list of possible causes of headaches while on phentermine is lack of sleep. Insomnia has been identified as one common side effect that accompanies phentermine intake. Getting more sleep than you need, not getting enough sleep and frequent sleep disruption can worsen your headaches while on phentermine (12).

Your brain relies on these sleep hours to refuel and recharge. Any type of sleep problems will deny your brain this much-needed adequate rest, and the end result could be a severe headache. To keep this headache trigger at bay, make sure you get about 9 hours sleep every night (9, 12). If phentermine interferes with your night sleep, you can take it first thing in the morning. Taking the drug early enough may help ensure its effects wear off before your bedtime (12).

How to get rid of headache while on phentermine

We have seen some of the possible causes of headaches while on phentermine. However, it is important we mention some ways you can get rid of headaches irrespective of the cause. Most phentermine side effects are known to vanish own their own as your body becomes accustomed to the effects of the drug (5). Here are some possible ways you can get rid of headache while on phentermine:

1. Do all you can to keep triggers away

The first step to keeping away headaches while taking phentermine is to prevent as many triggers as possible. Once you identify common triggers such as not taking enough water, skipping meals, or taking stimulants, do all you can to avoid them. Preventing headache remains the most effective way of dealing with it (9).

2. Take a painkiller

You can treat minor headaches with some over-the-counter painkillers. However, it is important you stick with the recommended dosage and ensure you take the painkiller with adequate water (9).

3. Consult your doctor

If the headache refuses to go away or becomes severe, try to get medical help as soon as possible. A severe headache can be a sign of an underlying medical condition and can be diagnosed by a physician. Also, any headaches that refused to go away after taking a painkiller is something your doctor should attend to as soon as possible (9).

Once you take these steps, you can enjoy your phentermine and all of its weight loss benefits without experiencing any discomforting headaches and head pains.