Phentermine Headache

Phentermine Headache

Headaches are one of the most common side effects of phentermine. In fact, almost half of users experience this uncomfortable reaction.

While the exact cause of phentermine headaches remains unknown, there’s no doubt that even a mild phentermine headache can significantly impact the quality of life.

This article is intended for informational purposes only. We are not doctors and the information below does not in any way constitute or substitute a professional medical opinion. Always contact a licensed medical professional for medical advice.

Does Phentermine Cause Headaches?

Woman with a phentermine headache
About 2 in 5 patients experience phentermine headaches

Not every patient experiences a phentermine headache, but head pain is still one of the most common reactions to this medication.

Headaches are most common at the beginning of treatment with phentermine. It often takes the body a few days or weeks to adjust this medication’s stimulant effects. Some people react more strongly than others and more sensitive patients sometimes experience a severe headache.

Certain lifestyle choices also increase the risk of headaches on phentermine. Phentermine users who consume caffeine, alcohol, or tobacco are more likely to experience headaches.

Alcohol and phentermine pills interact negatively and can cause chest pain, increased blood pressure, dizziness, depression, and sleepiness ( 1 ). Caffeine and nicotine are stimulants, so consuming them in combination with phentermine (an already-powerful stimulant) also increases the risk of adverse reactions.

If your phentermine headache is severe, persistent, or worsening, contact your doctor or seek immediate medical attention right away.

Why Does Phentermine Give Me a Headache?

Phentermine headaches occur for a variety of reasons and it is hard to identify the precise cause exactly of each pain. However, some common explanations for a phentermine headache include:

Taking a Stimulant

Phentermine weight loss pills can cause headaches as a result of the active ingredient’s stimulant effects. Phentermine is a sympathomimetic amine anorectic that stimulates the central nervous system to elicit a heightened state, similar to the “fight or flight” response ( 2 ).

One of the main effects of this activation response is the tightening and narrowing of blood vessels (vasoconstriction) in the digestive organs and the widening of blood vessels (vasodilation) in the skeletal muscles, heart, lungs, and brain. The chemical changes associated with this response also increase heart rate and blood pressure to provide the muscles with the oxygen and nutrients they need ( 4 ).

When cerebral arteries (blood vessels around the brain) dilate, blood flow increases to the brain. While brain tissue itself does not feel pain, the expansion of the blood vessels triggers surrounding nerves to send pain signals to your head and face ( 5 ). These signals may be responsible for your headache.

Woman drinking water to relieve a phentermine headache
Dehydration is a common cause of headaches


Another potential cause for a phentermine headache is dehydration.

This medication increases water needs and staying hydrated is critical to weight loss ( 6 ). Without enough water, tissues and blood vessels contract and electrolytes levels can get thrown out of balance, which triggers head pain.

So, the trick to treating and preventing this type of phentermine headache is maintaining adequate fluid consumption each day.

Not Eating Enough

Skipping meals or not eating enough is another common culprit in phentermine headaches.

Following an overly-restrictive diet often causes headaches because dramatic changes in blood sugar or diet can alter hormone levels. Hypoglycemia (low blood sugar), for example, causes headaches, confusion, nausea and other symptoms ( 7 ).

Long periods of fasting, such as those promoted by diets like intermittent fasting, may trigger (or exacerbate) a hypoglycemic headache.

woman yawning
Lack of sleep may worsen a phentermine headache

Lack of Sleep

Finally, skimping on shut-eye can cause headaches or even migraines. Insomnia is a common phentermine side effect, so sleep problems are a widespread trigger of phentermine headaches.

Interestingly: too much sleep, too little sleep, or poor-quality sleep can call trigger or exacerbate headaches ( 8 ). Sleep problems contribute to head pain because the brain uses sleep to recharge and refuel. If you’re depriving this vital organ of its much-needed rest, headaches ensue.

How to Get Rid of a Phentermine Headache

Like most side effects, phentermine headaches often decrease as your body adjusts to the medication.

However, if you are early in treatment and battling a bothersome phentermine headache, you’re likely wondering how to prevent a headache while taking Adipex or other brands of phentermine.

The first goal is to avoid headache triggers. Then, use this simple, five-step plan to get rid of a mild phentermine headache:

1. Stay Hydrated

Aim for at least two liters of water or other caffeine-free, calorie-free beverages per day. Drink more if your pee is darker than light yellow ( 9 , 10 ).

When you feel a phentermine 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 somewhere between 30 minutes and 3 hours.

Caffeinated and alcoholic beverages worsen dehydration.

healthy meal for weight loss
Low blood sugar from eating too little can exacerbate a phentermine headache

2. Eat Enough

To minimize blood sugar-related headaches, eat every 4-6 hours while awake. If you have diabetes (or other problems regulating your blood sugar, have meal or snack every 3-4 hours.

Eating too few calories, even if consumed periodically throughout the day, can also cause a hypoglycemic phentermine headache. Small snacks should be around 100-250 calories each, and women should consume at least 1200 calories a day, while men need 1500 calories a day to support basic biological functions.

Each time you eat, aim for a combination of complex carbs (whole grains, fruit, vegetables) and lean protein to keep blood sugar level.

3. Prioritize Sleep

To prevent a sleep-related phentermine headache, sleep for 7-9 hours every night ( 11 ). If the medication is keeping you up, try taking your pill first thing in the morning so that you give the phentermine as much time as possible to wear off before you head to bed.

4. Take an OTC Pain Killer

If your headache is relatively mild and short-lived, you may be able to treat it with over-the-counter (OTC) pain killers.

Common pain relievers you can take for a headache while on phentermine include Tylenol (acetaminophen), Motrin (ibuprofen) or Aleve (naproxen) ( 12 ). However, it is important not exceed the recommended dose or combine these medications, and always make sure to take the pills with plenty of water.

5. Go to the Doctor

See a doctor if your phentermine headache is not completely controlled with reasonable at-home treatment. Tell your doctor about any severe headache that gets worse, doesn’t go away, or interferes with your daily activities.

Call 911 or go to the hospital RIGHT AWAY if you have a “worst ever” headache. This can indicate a serious medical problem and needs to be assessed by a medical professional right away.

Back to All Phentermine Side Effects

  1. (2019, January). Phentermine and Alcohol / Food Interactions
  2. National Center for Biotechnology Information. PubChem Compound Database: CID=4771 (Phentermine).
  3. Linder, T., Ph.D., & Melby, A. E., Ph.D. (2017, April 14). Control of Arterioles.
  4. BBC Science & Nature. (2014, September 24). Human Body and Mind – Nervous System Layer.
  5. Marcus, D. A. (2004, May 24). What causes headaches?
  6. Popkin, B. M., D’Anci, K. E., & Rosenberg, I. H. (2010). Water, Hydration and Health. Nutrition Reviews, 68(8), 439-458. doi:10.1111/j.1753-4887.2010.00304.x
  7. The Migraine Trust. (n.d.). Hypoglycaemia.
  8. Rains, J., Ph.D. (n.d.). Sleep Disorders and Headache.
  9. NHS Inform. (2019). Hydration.
  10. Mayo Clinic Staff. (2017, September 06). Water: How much should you drink every day?
  11. National Sleep Foundation. (2014, November 13). How to Fall Asleep Fast.
  12. Davis, M., MD. (2008). Chapter 8: Appetite Suppressants. In The Millenium Diet: The Practical Guide for Rapid Weight Loss (pp. 75-88). Healthnets. ISBN: 978-0-615-20972-2.