Do You Have Insomnia From Phentermine? Read This!

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As a weight loss medication, phentermine successfully reduces appetite and increases energy levels mainly by increasing the release of key hormones which suppress hunger signals and boost concentration, alertness and the ability to sustain a more active lifestyle. However, as a stimulant,it is common for patients to experience insomnia from phentermine, making it difficult to get to sleep for many people who take this medication. Here we explain why insomnia occurs and what you can do to help minimize this side effect while taking phentermine.

Why Does Phentermine Cause Insomnia?

As phentermine is structurally similar to amphetamine, it has a similar impact on the central nervous system with respect to certain effects. Phentermine, like amphetamine is a psychoactive medication, which means that it crosses the blood-brain barrier to directly impact the central nervous system. There is a particular class of neurotransmitters called catecholamines, which are released when phentermine stimulates the neuron bundles in our brain. These include dopamine, epinephrine (adrenalin) and norepinephrine (noradrenalin). This causes phentermine to produce a significant but temporary improvement in both mental and physical abilities, including a positive impact in perception, mood, consciousness and behavior. It is this enhanced alertness and energy from phentermine which improves ability to concentrate on goals and maintain focus, in addition to being more motivated and able to sustain an active lifestyle.

However, this activity in the central nervous system can lead to difficulty sleeping as the brain finds it hard to ‘switch off’. Throughout the day, phentermine stimulates the brain to be more efficient and alert, increasing energy levels and concentration, but these enhanced levels of alertness can then interfere with your body’s ability to sleep, often despite feelings of tiredness. Some people believe that phentermine may inhibit the release of melatonin, the hormone which is released in accordance with the onset of darkness to bring about sleep, however, this is not thought to be the cause of insomnia from phentermine. Instead, it is more likely that the enhanced alertness which phentermine causes by stimulating the central nervous system inhibits the ability to sleep, despite the release of melatonin.


How to Avoid Insomnia From Phentermine

It is reasonably common for patients taking phentermine to experience insomnia during the first few days of their prescription, but if this side effect continues then you should consult your doctor to enquire about the possibility of a lower dose, or to see if he or she has advice for how you can help to minimize this problem.

Taking phentermine earlier in the day can help to reduce the possibility that you will have trouble sleeping when you go to bed, as the energy-boosting effects should wear off throughout the day. You should also try to expel the excess energy that phentermine gives you by exercising or increasing your daily activity level by taking the opportunity to walk as much as possible, such as, by parking at the far end of the parking lot, always taking the stairs, and going for a stroll during your lunch break. Although exercising increases general energy levels as well as energy levels following activity, exercise also aids sleep as it helps to regulate circadian rhythms and balance out hormones which help you sleep. If possible it is best to do more energetic exercise early in the day, as high-energy exercise causes an influx of adrenalin in the body that may inhibit sleep. However, more relaxing exercise such as yoga or Pilates are suitable for later in the day, especially if followed by a period of relaxation and stretching.

You should also try to disconnect as much as possible in the hours before bedtime with a reduced use of smartphones, computers and televisions. Instead, try relaxing with a bath or by reading a book. Ideally, your bedroom should be for the sole purpose of sleeping without interference from technological devices, and you should also avoid working in your bedroom as this association between work and rest can inhibit sleep by causing stress and hormone imbalances. You should also make sure your bedroom is a comfortable temperature for sleeping and that light from the street or other rooms is kept to a minimum. Lastly, avoid caffeine by refraining from drinking coffee, tea and soda in the hours before you go to bed. If your insomnia continues, you may wish to take something to aid your sleep but you must always consult your doctor before taking anything alongside phentermine, whether it is an over-the-counter remedy or a prescription sleeping medication, as it may cause a harmful drug interaction with additional side effects.

Lastly, if you find phentermine is just too strong of a medication for you, and you can’t manage to find a balance you’re comfortable with, then you may want to consider a weight loss alternative. At, we recommend Phen Caps, the #1 phentermine alternative. Phen Caps mimic the effects of phentermine, meaning they increase energy and suppress appetite and cravings. They contain no actual phentermine, but rather 9 innovative ingredients, and therefore do not have the same effect on your sleep patterns while also having no side effects! Maybe the most notable point, they are non-prescription, so can be bought online easily!

Have you experienced insomnia while taking phentermine? If so please feel free to comment below as we would like to hear if you have any feedback or advice for others with the same problem.

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114 Responses

  1. I started the 37.5mg a little over a week ago, I’m getting the insomia now which Im trying to figure out little tricks to help. I feel like when I don’t get enough sleep the pill does not seem to be as effective as it was the first few days. I’m still watching what I eat but I definitely are feeling hunger cravings more often and the side effect dry mouth is gone. Is this medication not as effective if you don’t get a good nights rest?

    • Hi Diane! Yes, actually 🙂 Due to hormonal imbalances, we experience more cravings and feel less satisfied when we’re sleep-deprived, with or without phentermine. Check out this article if you would like to read more about sleep and weight loss with phentermine.

  2. The first few days of the 37.5mg of phentermine did really great, I had no cravings all day. I take it within 30 minutes of waking up around 6:30am. After about a week I started having insomnia and never get a good night sleep. I now start having cravings sometimes as early as 11:30. Is the pill not as effective if I do not get a good night sleep? I am worried about dropping the dose down since I already having cravings on the 37.5mg.

  3. I am taking phentermine 37.5 mg once a day at 6:30 am when I wake up. I generally don’t have a problem going to sleep but 4am like clockwork I wake up. My question is if I take it at 6:30 am the previous morning is it still in my system at 4 am the next morning causing me to wake up at 4 am or is it just me waking up at that time ? I never did this before. I have been taking this for about 2 months. Thank you 😊

    • Hi Ann 🙂 The phentermine is still in your system at 4am the next morning, but in most people it wouldn’t be strong enough to be keeping you up. It is most likely just a change in your sleep schedule, but if it’s bothering you or getting worse, definitely check with your doctor. Hope you can get some sleep soon!

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