Phentermine With Diazepam Interaction

Jay asked

I took a 30mg phentermine at 7 AM yesterday morning. Today I was prescribed diazepam 5mg to be taken before bed. Is it safe to take the diazepam tonight as I haven’t taken phentermine since yesterday morning? How long does phentermine stay in the body?

Answer

There is no drug interaction between phentermine and diazepam and they can safely be taken together.

Having said that, they do have conflicting and potentially off-setting effects as phentermine is a stimulant while diazepam is a CNS (central nervous system) depressant.

Therefore, for an example regarding this issue, if you take diazepam for anxiety, you may find that it doesn't work quite as well if you take it with phentermine.

In terms of how long phentermine lasts, the duration of action differs depending on the specific product:

• The duration of action of the 8 mg capsules or tablets is about 4 hours.

• The duration of action of the 30 mg capsules or the 37.5 mg tablets is 12—14 hours.

Now, although it may not still be having active effects, it takes significantly longer than 12-14 hours for phentermine to be metabolized and eliminated from the body.

According to the prescribing information for phentermine, it has a half-life (the time it takes for our body to metabolize 50% of a drug) of 19-24 hours.

Generally, it takes at least 5 half-lives to elapse to consider a drug completely metabolized and eliminated from the body. This would equate to about 5 days with phentermine.

This is why before surgery, if you are taking phentermine, it is recommended to stop taking it at least one week prior, to avoid interactions with anesthesia and potential adverse cardiac effects.

In your situation, having taken phentermine more than 24 hours ago, the drug is still in your body but should be having minimal effects on you. There is no interaction with your prescribed diazepam so you can feel safe taking it.