Is It Safe To Take Benadryl With A Water Pill?

In our latest question and answer, the pharmacist discusses the use of Benadryl with water pills.

Is It Safe To Take Benadryl With A Water Pill?
May 21, 2019

Suzie asked

Can I take Benadryl with my water pill?

At a glance

  • Benadryl (diphenhydramine) doesn't have known interactions with 'water pills', but long-term use may mitigate their effects since Benadryl can cause urinary retention due to its anticholinergic properties.


Benadryl Capsules With Text - Taking With Water Pills

There are no known interactions between Benadryl (diphenhydramine) and 'water pills', also known as diuretics.

Having said that, the term 'water pill' is very broad, and could include everything from prescription diuretics (e.g. hydrochlorothiazide, furosemide, etc...) to over the counter products, like Diurex (which contains pamabrom).

This doesn't even include all of the herbal supplements that are thought to have diuretic properties, like dandelion and maritime pine.

Nevertheless, Benadryl doesn't have any published interactions with known diuretics.[1]

It is important to note, however, that the consistent use of Benadryl may cause urinary retention, which may decrease or negate the effects of a water pill (in terms of water retention). It shouldn't have any effect on blood pressure though.[2]

Benadryl Effects On Body Water

As mentioned, Benadryl doesn't have any known interactions with 'water pills' (which includes prescription and over the counter products that reduce total body water).

However, Benadryl does have fairly strong anticholinergic effects, especially when used long-term.[3]

Anticholinergic effects refer to a drugs ability to block the neurotransmitter acetylcholine. The effects are wide-ranging but include:[4]

  • Thickening of mucus secretions
  • Urinary retention
  • Pupil dilation
  • Dry eyes
  • Blurred vision
  • Increased body temperature
  • Dizziness
  • Sedation
  • Dry mouth

All of the above would be considered side effects of Benadryl, but the sedation it can cause is often the reason why it is used as an over the counter sleep aid and is included in sleep aid products (e.g. Tylenol PM).[5]

The specific effect of urinary retention generally only occurs in those that take Benadryl consistently for a long period of time. It also occurs more often in the elderly, who are more susceptible to the anticholinergic effects of Benadryl (which is one of the reasons it is not recommended in the geriatric population).[6]

Final Words

So overall, Benadryl likely won't interact with your 'water pill'.

It is important to know however that Benadryl itself can cause urinary retention, which may reduce how effective your water pill is.

The intermittent use of Benadryl likely won't be a problem, but if you plan on taking it all the time, you may notice that you are going to the bathroom less.

  1. ^ Elsevier Diphenhydramine Monograph. ClinicalKey
  2. ^ Pharmacology of Antihistamines. PubMed
  3. ^ Long-term use of diphenhydramine. PubMed
  4. ^ Managing Anticholinergic Side Effects. PubMed
  5. ^ Tylenol PM Manufacturer Website.
  6. ^ Commentary on the New American Geriatric Society Beers Criteria for Potentially Inappropriate Medication Use in Older Adults. PubMed

Ready for a more personal experience with your meds?