Is It Okay To Skip Doses Of Phentermine?

In our latest question and answer, the pharmacist discusses missing doses of phentermine.

Jun 28, 2018

Jen0609 asked

Can I skip days on Phentermine or are there health risks associated? I don’t feel I want to take it everyday. Sometimes I take a week break from it. I just want to make sure this doesn’t cause harmful affects on my body by doing so. I also know you are not suppose to drink alcohol while on it, while I’m not a huge drinker, if I know I’ll be having a few glasses of wine over the weekend, I will try to stop taking this a few days prior.


Phentermine sympathomimetic drug with similar effects to amphetamines. It is used most commonly as a short term (~8-12 weeks) weight loss aid. As phentermine has similar effects to amphetamine, it is thought to increase the release of various neurotransmitters in the brain, including norepinephrine and dopamine. It is also thought to increase levels of serotonin.

Can Phentermine Cause Withdrawal Symptoms?

Like other medications that significantly alter neurotransmitter levels (e.g. amphetamines, antidepressants) there is the chance of withdrawal symptoms if you have been taking the drug a long time and discontinue abruptly (or miss doses consistently). From the prescribing information for phentermine:

"Abrupt cessation following prolonged high dosage administration [of phentermine] results in extreme fatigue and mental depression; changes are also noted on the sleep EEG."

Depending on how long you have been taking phentermine is a major factor in whether or not you will experience side effects from missing doses. In general, one or two missed doses will not precipitate withdrawal or cause symptoms. In addition, as phentermine is generally used for short periods of time (~8-12 weeks), it isn't typically associated with major withdrawal reactions for most individuals.

Nevertheless, you should speak to your doctor regarding whether or not it is safe for you to "skip doses" or need a therapy change as they have your complete medical history. Your doctor can provide careful monitoring and symptom management is necessary.

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