Drug Arrows In Pills


There are four medications in question here:

The only drug interaction is between Klonopin (clonazepam), a benzodiazepine and Benadryl (diphenhydramine), a sedating antihistamine.

Benadryl - Klonopin Interaction

Use of Klonopin and Benadryl together could potentially cause additive side effects, such as:

  • Sedation
  • Dizziness
  • Central nervous system depression
  • Respiratory depression
  • Confusion

Due to the increased risk of side effects, they should be used together with caution, and you certainly should not operate heavy machinery or partake activities that require alertness until you know how these drugs affect you.

The most dangerous potential side effects, respiratory depression, would be uncommon at usual doses of Benadryl and Klonopin. Typically, cases of breathing problems only happen when an overdose occurs but it is nonetheless essential to aware of and report any breathing issues to your doctor should they occur.

You mentioned you took Klonopin 6 hours ago. While the most potent effects of the drug are likely to have worn off by now, it is still present in your body.

After taking a dose by mouth, it is quickly absorbed, and max concentrations are reached within 1 to 4 hours. The typical duration of action is between 6 and 12 hours and is recommended to be dosed up to three times daily.

Klonopin has a long half-life, the amount of time it takes our body to eliminate 50% of a drug. It generally takes around 5-6 half-lives for a drug to be eliminated. The prescribing information lists Klonopin as having a half-life between 19 and 50 hours.

If you wait 6 hours between dosing of Klonopin and Benadryl, Klonopin will likely still be having medicinal effects on you, but it typically would be declining by this time. Nevertheless, it stays in your body for days.

To truly avoid any sort of interaction between Benadryl and Klonopin, doses would need to be separated by a considerable margin of time (4-7 days). In general, this isn't necessary and after about 12 hours, additive effects should be minimal.

Final Words

These drugs are often used together, but should only be done under the direction of your doctor. The risk of severe side effects is minimal for most individuals, with the combo most likely causing you to feel more tired or sedated than usual.


Taking Benadryl (diphenhydramine) and Klonopin (clonazepam) can result in additive side effects, such as sedation and dizziness. Serious side effects, such as respiratory depression, are rare at directed doses.

  • Elsevier ClinicalKey: Clonazepam (Accessed 1/28/19)
  • Elsevier ClinicalKey: Diphenhydramine (Accessed 1/28/19)
  • Klonopin Prescribing Information (Accessed 1/28/19)