Antihistamines are antiemetics?
June 2, 2007 6:03 PM   Subscribe

Is it true that an over the counter antihistamine like Benedryl (U.S. name) will inhibit vomiting?
posted by mrhappy to Health & Fitness (22 answers total) 2 users marked this as a favorite
In a fashion. Diphenhydramine is actually the drug in question, and due to the details of it's function that's beyond my ken, it can inhibit vomiting.
posted by SpecialK at 6:07 PM on June 2, 2007

(However, it will only work on SOME reasons for vomiting, and someone more smarter than myself will have to explain why. I wouldn't take it to inhibit vomiting, mostly because you can't get an effective amount into the bloodstream before you vomit it back up, dig?)
posted by SpecialK at 6:08 PM on June 2, 2007

Also -- this question could've been answered with a really quick google.
posted by SpecialK at 6:09 PM on June 2, 2007

Not all antihistamines are anti-emetics, but some are. Dramamine is the most famous, I think. Cyclizine is the big one here in teh UK. They work by dulling sensation in the inner ear, which is believed to reduce your sense of motion, so they're often used for travel sickness, but they work for other forms of nausea as well -- hence Cyclamorph, in which the cyclazine reduces nausea induced by the morphine.
posted by PeterMcDermott at 6:11 PM on June 2, 2007 [1 favorite]

according to wikipedia, it basically just slows down your systems, which keeps the vomiting reflex at bay. it also makes you tired, constipated, and generally dries you out (you produce less saliva, tears, etc).
posted by thinkingwoman at 6:40 PM on June 2, 2007

Isn't it the case that there aren't really any true anti-nausea drugs?
posted by Ethereal Bligh at 7:10 PM on June 2, 2007

Dramamine is the most famous, I think.

Dramamine is Benadryl is diphenhydramine (well, okay, one is dimenhydrinate, but that seems to get metabolized into diphenhydramine + a salt in the body). Diphenhydramine is also a common sleep aid.

The point being that if you want diphenhydramine, it's worth looking in the motion sickness, antihistamine, and sleep-aid sections, as the prices can be notably different.
posted by ROU_Xenophobe at 7:15 PM on June 2, 2007

Theoretically - yes.

Practically - no. I got all excited about this in pharmacy school when I learned about what receptors it blocks. I experimented on my husband one unfortunate night when he was ill. I gave him some of the children's Benedryl suspension, figuring the suspension would be absorbed faster than the tablet. Not fast enough. It all came back up.

Google revealed that the military is in fact researching using diphenhydramine for this purpose. In suppository form. Personally, I think I'll stick with the puking. I think Emetrol is an over the counter option.

There is a prescription drug called Zofran that is supposed to be a wonderful anti-emetic used with cancer patients a lot. It's also sometimes prescribed for pregnant women. In fact, one of our professors told us that the drug was such a lifesaver for a pregnant friend of hers that the woman ended up naming her daughter Zoe Anne after the drug.
posted by selfmedicating at 7:16 PM on June 2, 2007

IANAPharm, I just get hives a lot.

Benadryl can slow down vomiting/stop it in some people. Not as well as dramamine or the other related ones, but it can. Your average 'antihistamines' affect H1 histamine receptors, which are responsible for various things, including motion sickness, hives, itching, and some smooth muscle things - including the GI smooth muscles, aka vomiting. (H2 receptors are for gastric acid; the newer anti-acid drugs are H2 antihistamines.) Different antihistamines on the market are tweaked to have a greater or lesser effect on each of these, versus sedation. Again, personal reaction can vary.

Anecdotally: I used it on a friend who was sick, knowing that one antihistamine wasn't going to kill her, and might help her (more importantly: me) get some sleep. She was vomiting/dry heaving on the hour, not just a once-event thing. It did slow down afterwards - for whatever reason. It may have just knocked her out enough that it slowed everything down.
posted by cobaltnine at 7:19 PM on June 2, 2007

As a nurse (ing student) I have seen this on the floors all the time. People who tend to get sick after taking certain medications (or people who just feel nausea) are given this regularly. It does seem to work on most people. The point is to keep the medication down, so giving it to someone who is about to throw up is not a very practical idea. If we know someone is going to feel sick after getting a medication, we pre-medicate with benadryl at least 30 minutes prior.
posted by nursegracer at 7:42 PM on June 2, 2007

Response by poster: Great. Thank you for your thoughtful, informed answers, and for the one Google snark. May the internet gods bless you.
posted by mrhappy at 11:02 PM on June 2, 2007

The two best anti-emetics I have found are marijuana, which unfortunately has a relatively short effect when infected with particularly nasty bugs, and Prochlorperazine, which can be administered topically.

Unfortunately, one is illegal, and one requires a prescription. Prochlorperazine is amazing, though. Unlike others that only work for me if taken before the onset of nausea, that gel just stops the nausea in its tracks.
posted by wierdo at 3:31 AM on June 3, 2007

Ginger has always gotten rid of my nausea.
posted by Zarya at 5:05 AM on June 3, 2007

when I first was having chemo I was prescribed benadryl as part of the post chemo anti-nausea regimen. (I also had zofran and something else.) But I was always zonked for several days because benadryl knocks me out for twice the expected time. I told my cancer doc about being knocked out, and he said, "oh, the benadryl is really optional. try not taking it!"

So I left it out and the other drugs did a good enough job keeping the nausea away. I'd had no idea he considered it optional!
posted by anitar at 9:07 AM on June 3, 2007

Around 40 years ago, they passed out a very heavy duty antihistamine for morning sickness, and many pregnant women slept through the entire thing. About 35 years ago, they discovered it could cause birth defects and took it off the market. The name of the stuff eludes me by now.
posted by unrepentanthippie at 9:48 AM on June 3, 2007

Around 40 years ago, they passed out a very heavy duty antihistamine for morning sickness, and many pregnant women slept through the entire thing. About 35 years ago, they discovered it could cause birth defects and took it off the market. The name of the stuff eludes me by now.

You're thinking of thalidomide, but it's not an antihistamine.
posted by Ethereal Bligh at 10:12 AM on June 3, 2007

No, it wasn't thalidomide, that was a tranquilizer or psychotropic. This was an actual antihistamine.
posted by unrepentanthippie at 10:45 AM on June 3, 2007

posted by unrepentanthippie at 10:47 AM on June 3, 2007

Ah. Thalidomide fit the bill well enough that I figured that's what you were thinking of. Sorry to have underestimated you. :)
posted by Ethereal Bligh at 6:31 PM on June 3, 2007

Benedictin = B6 + Unisom (regular strength). Off the market around 1983. Unisom = antihistamine. The pregnancy category of Doxylamine (and other antihistamines) fluctuates between A and B, depending on the current litigious climate. Given the current state of OB lawsuits, it won't be back on the market any time soon, even though it's actually likely safe.
posted by cobaltnine at 6:35 PM on June 3, 2007

From this page on the treatment of emesis:
Classes of antiemetic drugs
  1. Muscarinic receptor antagonists Good for prevention of motion sickness.
    • scopolamine (Transderm-Scop®)
  2. H1 antihistamines

    For motion sickness. Most antihistamines have additional anticholinergic action. Typical side effects of H1 antihistamines include drowsiness and loss of coordination. The newer antihistamines (e.g., Hismanal, Claratin, Allegra) which do not cross the blood-brain barrier would not be useful.

    • dimenhydrinate (Dramamine)
    • several clizines (e.g., cyclizine)
    • diphenhydramine (Benadryl)
    • promethazine
    • hydroxyzine (Vistaril)
  3. Antidopaminergic drugs

    Most of these drugs are also used as antipsychotic agents. They have antimuscaranic action.

    • chlorpromazine
    • droperidol (Inapsine)
    • prochlorperazine
    • metoclopramide (used as antiemetic)
    • fluphenazine
    • domperidone (used as antiemetic)
    Droperidol has a "black box" warning and for this reason should not be lightly used for control of emesis.

  4. Benzodiazepines

    Good for anticipatory nausea and vomiting before cancer therapy. Also useful for vestibular disorders.

    • diazepam (Valium)
    • lorazepam (Ativan)
  5. Corticosteroids

    Mechanism of action not clear. May be related to the inhibition of arachidonic acid release. Dexamethasone is reportedly as effective as ondansetron for prevention of PONV (Wattwil et al. 2003)

    • dexamethasone
    • methylprednisolone
  6. Cannabinoids

    Acts on higher centers in the cortex. -- dronabinol

  7. 5-HT3 receptor antagonists

    This class of drugs is the most effective treatment available for prevention of severe vomiting due to cancer chemotherapy and cause little toxicity; about 85% of patients attain complete control of emesis and nausea. Usually given in combination with dexamethasone. Also widely used for PONV, but less effective (20% reduction, Tramer et al, Anesthesiology 87:1277-89, 1997). Although animal studies suggest it should not work for vestibular problems, empirically it is also often effective in this context. Unfortunately, this is a very expensive drug (about $20-$40/dose or even more). It is very convenient and can be taken as a sublingual preparation.

    • ondansetron
    • tropisetron
    • granisetron (approved for IV injection only)
    • dolasetron (investigational)
  8. Miscellaneous

    • benzquinamide
    • diphenidol (Vontrol) -- little used because of side effects (hallucinations)
    • trimethobenzamide (Tigan)
    • verapamil (Calan) -- useful for migraine associated vertigo and cyclic vomiting.
posted by Ethereal Bligh at 7:16 PM on June 3, 2007

No apology needed; it was a good guess. I should have googled first. :)
colbaltnine: Thank you for the translation.
posted by unrepentanthippie at 7:48 PM on June 3, 2007

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