Phentermine promotes weight loss by reducing appetite and increasing energy levels. Itdoes this primarily by triggering the release of hormones that suppress hunger signals and boost concentration and alertness.
However, as a result of this increased energy and alertness, it is common for patients to experience phentermine insomnia. When persistent, this phentermine side effect can make getting enough sleep a frustratingly difficult task.
Yes, insomnia is one of the most common side effects of phentermine pills .
In fact, more than 1 in 2 patients experience phentermine insomnia, making it the second-most reported side effect of phentermine .
Phentermine functions as a central nervous system (CNS) stimulant, in many ways similar to amphetamine.
The medication is thought to function by increasing concentration of a class of neurotransmitters called catecholamines, including dopamine and norepinephrine (noradrenalin). As such, when a dose of phentermine causes a surge of these chemicals, it produces a temporary, albeit significant, decrease in appetite and boost in energy .
However, that same stimulation can also cause difficulty sleeping.
Phentermine stimulates the brain to be more efficient and alert, increasing energy levels and concentration to promote weight loss throughout the day. Unfortunately, these enhanced levels of alertness can also continue into the night and interfere with your body’s ability to sleep, even despite feelings of tiredness.
Patients often experience insomnia during the first few days or weeks of treatment, but it should improve as your body adjusts to the medication.
If this side effect continues (e.g. you are still experiencing phentermine insomnia after 2 months), consult with your doctor. He or she may suggest a lower dose or offer additional advice about what can help with insomnia from phentermine.
Phentermine insomnia can keep you up for hours or even days at a time, despite intense feelings of tiredness. It is common, then, to wonder how to fall asleep on phentermine. There is no magic phentermine insomnia cure, but there are some strategies to help phentermine insomnia go away.
If you find yourself battling recurrent insomnia, try these five simple tips to sleep when on phentermine:
Take phentermine first thing in the morning to reduce the risk of phentermine insomnia. Most patients 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, doctors and pharmacists recommend taking the last dose pill at least 8-10 hours before bedtime to minimize medication-related insomnia.
It is best to steer clear of caffeinated beverages while taking phentermine due to the medication’s stimulant effects. Consuming caffeine while taking phentermine can cause or exacerbate adverse reactions like racing heart, chest pain or high blood pressure .
Regardless of whether or not you are taking phentermine, excess caffeine consumption also interferes with your ability to get enough restful, reparative sleep.
Avoid caffeine by refraining from coffee, caffeinated tea, soda (particularly colas) and energy drinks, especially for several hours before you go to bed.
One way to expel the excess energy and prevent insomnia while taking phentermine is to increase your daily activity level. This can be either in the form of formal workouts or simply taking the opportunity to move throughout the day.
Getting to the gym early in the morning seems to hold the most benefit in terms consistency and overcoming insomnia. In fact, the National Sleep Foundation notes that, “people who work out on a treadmill at 7:00am 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.” 
No time to go for a walk in the morning? Not to 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 right before bed, opt for a more relaxing exercise like yoga or stretching .
Research shows that too much screen time negatively affects users’ mental health and can interfere with restful sleep . So, try to disconnect as much as possible in the late evening hours by reducing use of smartphones, computers and televisions.
Your bedroom should be for the sole purpose of sleeping: without interference from technological devices, work or other distractions. This singular purpose space helps signal your brain that the bedroom is a place for sleep and rejuvenation, not stress and wakefulness.
Finally, take a moment to consider the physical environment in your room as well. Make sure your bedroom is a comfortable temperature for sleeping (preferably on the cooler side) and that light from the street or other rooms is kept to a minimum.
At least once during their phentermine journey, many patients wonder, "Can you take sleeping pills with phentermine?" The answer is simple: you need to ask your doctor.
Some combinations are dangerous, while others can help you sleep and promote greater weight loss. However, sleeping pills are not a safe option for all patients so it is vital that you speak directly with your prescribing physician.
Phentermine and melatonin are a common combination, especially for patients struggling with insomnia. However, the specific drug interaction remains undefined and some doctors warn about the two substances’ opposing effects.
Therefore, it is vital for each patient to check with their doctor and pharmacist before combining phentermine and melatonin, or any other medication or supplement.
Click here to read more about supplements to take with phentermine.
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6. National Sleep Foundation. (2018). What Time of Day to Exercise for Better Sleep.
7. 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