Can You Take Adipex-P (Phentermine) With Cold Medicine?

Some are safe, but not all!


I've been taking Adipex-P for two months now and this morning I woke up with a beginning of a cold. What cough medications can I take that are safe for me? Also, are there daytime medications that I can take? Thank you.

Asked by JJohnson On Aug 15, 2018

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Aug 16, 2018

Person With ColdPhentermine (Adipex-P) has several interactions with over the counter cough/cold medications and are important to be aware of.

Specifically, caution needs to taken before combining phentermine with:

  • Dextromethorphan (cough suppressant)
  • Pseudoephedrine (nasal decongestant)
  • Phenylephrine (nasal decongestant)

We discuss these in more detail below.

Phentermine With Dextromethorphan

Both phentermine and dextromethorphan can increase levels of the neurotransmitter serotonin (1, 2). This increases the risk of a rare but serious condition known as serotonin syndrome, which is characterized by several symptoms, including (3):

  • Agitation
  • Anxiety
  • Hyperthermia
  • Mental status changes
  • Cognitive impairment
  • Seizures
  • Rigidity
  • Sweating
  • Nausea
  • Vomiting

While the overall risk of serotonin is relatively low for most individuals, combining medications with serotonin effects increases the risk (4). 

There is some controversy regarding how strong an effect dextromethorphan has on serotonin. Some studies show that when taken at recommended doses, it doesn't increase levels (5). Others studies however, have presented case reports in which serotonin syndrome occurred on usual doses (6). It is important to speak with your doctor before combining phentermine with dextromethorphan.

It is also important to be aware that dextromethorphan is a very common ingredient in over the counter cough/cold medications. For example, it is included in NyQuil, DayQuil and Tylenol Cold & Flu. Be sure to read the labels of the over the counter products you plan on purchasing.

Phentermine With Pseudoephedrine Or Phenylephrine

Taking phentermine with psuedoephedrine or phenylephrine can increase blood pressure and heart rate. Phentermine is a stimulant medication, chemically similar to amphetamines. Both pseudoephedrine and phenylephrine have mild stimulating properties (7). Phentermine with nasal decongestant can have additive effects.

Phentermine should not be used with either drug unless specifically directed by your doctor.

What Cold Medications Are Safe?

While you should avoid any of the medications previously discussed with phentermine unless you speak with your doctor, the following are considered to have no drug interactions:


Antihistamines are considered safe to take with phentermine. While not often classified as 'cold' medications, antihistamines can help many related symptoms, include:

  • Runny nose
  • Congestion
  • Watery eyes
  • Post nasal drip (which could cause a cough)
  • Insomnia (with sedating antihistamines like Benadryl)

Over the counter antihistamines include:

  • Benadryl (sedating)
  • Zyrtec
  • Allegra
  • Claritin

Pain Relievers

Both NSAID pain relievers (e.g. Advil, Aleve) and Tylenol (acetaminophen) are considered safe with phentermine. They can provide symptomatic relief for a variety of cold symptoms, including fever and headaches.


Mucinex (guaifenesin) is considered safe to use with phentermine. Mucinex helps to relieve chest congestion and can be helpful for post nasal drip.


Most "natural" products for cough relief are safe to use, including ones with honey. In addition, cough drops with menthol or ones with anesthetics (e.g. benzocaine) are considered safe.

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Dr. Brian Staiger is a licensed pharmacist in New York State and the founder of He graduated from the University At Buffalo with a Doctor of Pharmacy degree in 2010. He has been featured in numerous publications including the Huffington Post as well as a variety of health and pharmacy-related blogs. Please feel free to reach out to him directly if you have any inquiries or want to connect! He's answered thousands of medication and pharmacy-related questions and he's ready to answer yours! Office: 716-389-3076

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