Insomnia can be induced by phentermine usage. This can be worrisome because you wouldn’t want to go through the night without sleep or your sleep cut short simply because you are trying to shed some pounds.

Having a good night sleep is very beneficial to your health. This is because; it can boost your immune system, help prevent weight gain, strengthen your heart, increase productivity, and as well, improve your memory. But taking phentermine can cause you sleep deprivation, which is of no health benefits.

The good news is that insomnia can be prevented while taking the drug. This means that, you can use phentermine and also sleep well enough at night.

What is phentermine and what is it used for?

Phentermine is a prescription medication or drug which is used to treat obesity. It is taken orally, together with diet and exercise for few weeks, as prescribed by a doctor.

Side effects of phentermine

While taking phentermine, you may experience the following side effects;

  • Hypertension (high blood pressure)
  • Restlessness
  • Sex drive changes
  • Insomnia
  • Erectile dysfunction (in men)
  • Fatigue
  • Headache
  • Dry mouth
  • Constipation
  • Period problems (in women)

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Why does phentermine cause insomnia

The drug acts as a Central Nervous System (CNS) stimulant, just like amphetamine. It does this by increasing the levels of dopamine and norapinephrine, which results to a temporary and significant boost in energy and decrease in appetite. This helps you to lose weight and at the same time cause sleeping difficulty; which sometimes, extends into the night and make it hard for you to fall asleep, even when you are tired and weak.

How to deal with insomnia while taking phentermine.

A lot of people wonder how to fall asleep at night while taking phentermine. If you find yourself battling recurrent insomnia, try these five simple tips to sleep better. Although there is no magic cure for phentermine induced insomnia, but these simple strategies can help your sleeplessness go away.

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1. Take your prescribed phentermine drug earlier.

Take the phentermine dose as prescribed by the doctor first thing in the morning to reduce the risk of phentermine induced insomnia. Most patients prefer to take their pill on an empty stomach, either 30 minutes before or 1-2 hours after breakfast.

Phentermine reaches its maximum potency in the blood after about 1-3 hours and is completely absorbed in 4-6 hours, depending on physical activity and the amount of food in the stomach. However, most patients feel phentermine’s energy-boosting effects for closer to 10-14 hours. So, it is recommended to take the last dose pill at least 8-10 hours before bedtime to minimize medication-related insomnia.

2. Reduce or stop caffeine usage.

Too much consumption of caffeine interferes with your ability to get enough restful, reparative sleep. The best option for you is to steer clear of caffeinated beverages while taking phentermine because the medication already has strong stimulant effects. Consuming caffeine while taking phentermine can cause adverse reactions like racing heart, chest pain or high blood pressure.

You need to avoid anything that contains caffeine such as coffee, caffeinated tea, colas and energy drinks. Instead, opt for caffeine-free, sugar-free options like water, milk or herbal tea. This can be hard for some people to do but why should you not do it if you really want your sleep back.

3. Exercise

One way to burn off the extra energy from phentermine and reduce insomnia is to increase daily activity. This can come in the form of either workouts or simply moving more throughout the day.

Evidence indicates that working out first thing in the morning is best for overcoming insomnia. In fact, people who work out on a treadmill at 7:00 am sleep longer, experience deeper sleep cycles, and spend 75 percent more time in the most reparative stages of slumber than those who exercise at later times that day”. But don’t worry: afternoon workouts also help combat insomnia. The only time of day that exercise does not help with insomnia from phentermine is late at night.Aerobic exercise too close to bedtime increases core body temperature and signals your body not to sleep.

If you have some extra energy late at night, opt for a more relaxing exercise like yoga or stretching.

4. Disconnect 1 to 2 hours before bedtime

Too much screen time adversely affects your mental health and can interfere with sleep. So, you need to try to disconnect 1-2 hours before bedtime by turning off smartphones, computers and televisions. Use that time to read a book, meditate or take a warm bath to wind-down instead.

5. Make your bedroom a sleep room.

You have to keep your bedroom free of technological devices, work or other distractions. When you design your room as a space for rest and relaxation you are sending signal to your brain that the bedroom is a place for sleep, not stress and wakefulness. Make sure your bedroom has a comfortable temperature for sleeping (preferably on the cooler side) and that light from the street or other rooms is kept to a minimum.


Cosentino, G., Conrad, A., & Uwaifo, G. (2013). Phentermine and topiramate for the management of obesity: A review. Drug Design, Development and Therapy, 267. doi:10.2147/dddt.s31443

Aaron. (2020, January), Phentermine: What You Need To Know – How to lose weight

SCL Health. (2018, September). The benefits of getting a full night’s sleep (2019, January). Caffeine and Phentermine Drug Interactions.

National Sleep Foundation. (2018). What Time of Day to Exercise for Better Sleep.

Thomée, S., Härenstam, A., & Hagberg, M. (2012). Computer use and stress, sleep disturbances, and symptoms of depression among young adults – a prospective cohort study. BMC Psychiatry, 12(1). doi:10.1186/1471-244x-12-176

Disclaimer: The information contained in this article is provided as an information resource only. This information should not be used as a substitute for professional diagnosis and treatment. You should always consult your doctor or other healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.

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