woman with headache on phentermine

Your Phentermine Headache: Causes and Solutions

General Phentermine Questions?
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Headaches are one of the most common side effects of phentermine. In fact, almost half of respondents in our new user poll reported experiencing this uncomfortable reaction. The pain may be caused by either the pills or related lifestyle changes, but regardless, even a mild phentermine headache can really impact your quality of life. So, we’re here to help you understand some possible causes and solutions for this frequent side effect!

IMPORTANT WARNING: Mild headaches are a common side effect of phentermine. However, if your headache is severe (“worst ever”) or won’t go away, seek immediate medical attention. This pain could be symptomatic of a much more serious issue.

Who Gets Headaches on Phentermine?

While not every person taking phentermine experiences headaches, it is still one of the most common reactions to this medication. New users and those that consume other substances alongside phentermine are more likely to experience head pain, as well as other negative side effects.

New Users

Headaches – and side effects in general – are more common when you first start phentermine. This is because your body takes some time to adjust to phentermine’s effects. As with all chemical substances, some people react more strongly than others to phentermine’s active ingredient. So, if you’re especially sensitive, headaches may occur as part your body’s adjustment to the new medication.

Regardless, if your headaches are especially severe or persistent (more than a couple of days), consider speaking to your doctor. He or she may want to decrease your initial phentermine dose, or adjust your schedule. This change could help you enjoy the effects of phentermine without experiencing so many side effects. Phentermine can still be highly effective at lower doses, so you should not be concerned that phentermine will stop working. Still, never adjust your phentermine dosage or schedule without speaking to your doctor first.

Drinkers & Smokers

Lifestyle choices also increase your risk of headaches on phentermine. Due to the chemical interactions between substances, phentermine users who smoke, consume caffeine or drink alcohol are more likely to experience headaches. The increased risk of side effects helps explain why indulging in these vices is discouraged while taking phentermine.

Alcohol and phentermine should not be mixed because they are known to be a problematic (and potentially dangerous) combination. Alcohol interacts with phentermine to increase dizziness, sleepiness and stress on your organs. It can also contribute to increased blood pressure. So, you should strive to avoid all alcohol while taking phentermine.

The other two substances – caffeine and nicotine – are stimulants. It’s not advisable to combine phentermine with any other stimulant given that the medication already contains a very powerful upper. Users who choose to combine outside stimulants are at increased risk for negative side effects, including headaches.

Headaches are one of the most common side effects of phentermine. Click here to learn more about possible causes & solutions!

What Causes Headaches?

Phentermine headaches may occur for a variety of reasons and it is hard to identify exactly what causes each individual headache. Therefore, it proves beneficial to know about the various posibilites. Below we discuss some potential causes  of phentermine headaches – both related to the medication itself and associated lifestyle changes.

Taking a Stimulant

One of the main reasons phentermine causes headaches is because of its stimulant effects. Phentermine is a sympathetic amine, so it creates effects in the body similar to the rush of adrenaline we experience when we have a “fight or flight” response. One of the main effects of this response is vasoconstriction, or the tightening and narrowing of blood vessels, in your digestive organs and vasodilation, or widening of your blood vessels, in your skeletal muscles, heart, lungs and brain. The chemical changes associated with this simulated stress response also make your heart beat harder and faster to provide your muscles with the oxygen and nutrients they need. As a result, many phentermine users experience an increase in blood pressure, as well as an increase in heart rate, after taking the medication. These cardiovascular changes are the main reason why it’s so dangerous to take phentermine if you have a history of heart disease or high blood pressure.

They also help explain the commonality of headaches. Just like too much coffee can give you headaches, so to can a high dose of phentermine. When cerebral arteries dilate (as part of the synthesized “fight or flight” response), blood flow increases to the brain. While brain tissue itself doesn’t feel pain, expansion of the blood vessels triggers surrounding nerves to send pain signals to your head and face. These signals may be responsible for your phentermine-related headache.

If you’re on a high dose of phentermine and the headaches (or other side effects) aren’t going away, consider speaking with your doctor about adjusting your dose down. Never adjust your dosage or schedule without first speaking with your prescribing doctor.


Another potential cause for phentermine-related headaches is dehydration. As your doctor probably mentioned, it’s important to drink plenty of water while taking phentermine. Staying hydrated is important to protect your kidneys, control cravings and nourish your skin. It’s also helpful in managing the common phentermine side effect of dry mouth (xerostomia). While xerostomia is not caused by dehydration, forgetting to drink enough water definitely makes it worse.

With the high fluid needs on phentermine, it’s easy to get dehydrated. And, whether you’re on phentermine or not, drinking too little water can cause headaches. Dehydration causes tissues and blood vessels to contract, as well as electrolyte imbalances, both of which trigger pain signals in your head. So, the trick to preventing – and treating – this type of headache is adequate fluid consumption. Aim to drink enough water to keep your pee light yellow and your tissues hydrated. When you feel a headache coming on, drink 2-3 glasses of water right away. If the headache is caused (or worsened) by dehydration, this should start bringing relief in about 30 minutes to 3 hours. Just remember that caffeinated and alcoholic beverages dehydrate you more, so go for caffeine-free, sugar-free drinks if your goal is proper hydration.

woman at work with phentermine headache

Skipping Meals

Another common cause of phentermine headaches is skipping meals or not eating enough. Following an overly-restrictive diet can cause headaches because of either low blood sugar or stress hormones, or both.

Our cells use glucose (aka blood sugar) for energy. Among our bodily cells, neurons consume the most glucose per ounce. So, tight control of glucose is critical to keep our brain functioning at top speed. It makes a lot of sense, then, that headaches are one of the first symptoms of your blood sugar being thrown off-balance. If you develop hypoglycemia, or low blood sugar, it can cause headaches, confusion, nausea and other symptoms. The risk of glucose-related headaches is higher in people with diabetes, those who fast for long periods of time and people with high-sugar diets.

Your body also releases stress hormones when you fast, which may trigger (or exacerbate) headaches in some people.

To minimize your risk of hypoglycemic headaches, make sure to eat every at least 4-6 hours while you’re awake. If you have diabetes or trouble regulating your blood sugar, it may be better to aim for a meal or snack every 3-4 hours. When you’re busy and don’t have time to eat a proper meal, try to plan a meal replacement shake or healthy snack to eat on-the-go. In terms of quantity, aim for at least about 1200 calories per day if you’re a woman, or about 1500 calories per day if you’re a man on phentermine, to support basic biological functions.

Lack of Sleep

Finally, skimping on shut-eye can cause headaches (or even migraines) in many people. Insomnia is a common side effect of phentermine, so this is widespread trigger of phentermine headaches. Too much sleep, too little sleep or disrupted sleep patterns can call trigger or exacerbate headaches.

Sleep problems contribute to head pain because your brain uses sleep hours to recharge and refuel. If you’re depriving this vital organ of its much-needed rest, headaches can ensue. The pain may present as either a migraine or tension-type headache. To prevent this trigger, aim for around 7-9 hours of high quality sleep per night. If phentermine is keeping you up, try taking your pill very first thing in the morning so that you give the medication as much time as possible to wear-off before you head to bed.

How Can I Get Rid of My Headache?

We’ve discussed some of the main triggers for phentermine headaches, but regardless of what’s causing the headache, you’re probably most interested in getting rid of it. Like most phentermine side effects, your headaches will probably decrease or disappear once your body gets used to the medication. Still, you have a couple of options to manage this side effect in the meantime.

1) Prevent triggers: First and foremost, prevent your headache triggers if possible. Whether it’s an afternoon coffee, skipping breakfast or forgetting to drink water – try to identify your triggers and avoid them. The best way to deal with headaches is to prevent them in the first place when you can.

2) Use an over-the-counter pain killer: If your headache is relatively mild and passing, you may be able to treat it with over-the-counter (OTC) pain killers like Advil or Tylenol. Do not exceed the recommended dose and make sure to take the pills with plenty of water.

3) See your doctor: If your headache won’t go away, or turns severe, seek medical attention right away. A “worst ever” headache can indicate a serious medical problem and should be immediately assessed by a medical professional. Similarly, a headache that won’t go away and/or that is interfering with your daily activities is something your prescribing doctor should know about.

Have you suffered with headaches on phentermine? What did you do to cope? Did they go away eventually? Share your experiences in the comments section below!

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