What Side Effects Do People Experience With Phenergan? Real Reddit Users Share

Phenergan (generic promethazine) is an antihistamine used for nausea, allergies, sleep, and motion sickness, among other uses. It’s well-known for being very sedating, but how does it really affect people day to day? We’ve gathered Reddit users’ own reports of side effects — both common and unusual — to give a more grounded view beyond the medical leaflets.

Here’s what people who’ve used Phenergan say — the good, the uncomfortable, and the weird.

What Reddit Users Say About Phenergan’s Side Effects

Many users mention that Phenergan does work for nausea or sleep relief, but nearly always accompanied by strong side effects—especially tiredness and grogginess.

"It works well for my nausea but it makes me so dang drowsy!"

"I take promethazine … it’s a miracle for me!!! … The drowsiness goes away after a few months"

Sedation, Tiredness, and Feeling Out of It

One of the most common complaints: Phenergan knocks people out hard. It’s not just a little sleepy — it can be extreme.

"This week I finally broke … supplemented with phenergan yesterday … Today I have been completely out of it. The nausea has subsided quite a lot, but my whole body feels like jello and when I get up to move it feels like walking through cement."

"I know it’s common to make you sleepy … but this one makes me so tired I literally can’t wake up for more than a couple moments for 10-12 hours, and I’m still really drowsy for another 8-12 hours after that."

Changes Over Time / Tolerance

Some people report that the effects (especially the sedation) get less intense with time.

"At most Phenergan makes me drowsy but as my body has gotten used to it it doesn’t affect me much anymore other than handling nausea and letting me keep some stuff down."

Digestive and Gastrointestinal Discomfort

There are also reports of nasty stomach reactions, especially when using suppositories or after stopping/starting the drug.

"Took 2 doses and had these effects both times so I am pretty confident it is just how my body reacts to this med. First of all, it felt like I put hot sauce into my behind. SO MUCH BURNING! then, within about 10 min, I had horrific stomach cramps. The ones you get when you have food poisoning and are about to get horrific diarrhea."

"I take promethazine it’s a miracle for me!!! … I took it at night and it did make me feel a little woozy the following day, though but nothing I couldn’t manage, I could still go to work."

Effects On Sleep & Dreams

Phenergan is often used for sleep, but it doesn’t always work smoothly.

"I have been taking 2 25mg tablets a night and my sleep has improved a lot. They seem to stop the noise in my head and I’m sleeping in 20 to 30 minutes but I'm only getting 5/6 hours of good sleep then it's constant vivid dreams and nightmares and waking every hour."

Other Side Effects & Mental Effects

Besides sedation and digestive issues, users also report mental or perceptual oddities — including confusion, struggling to get out of zombie mode, and sometimes anxiety or restlessness.

"I take promethazine … I know extreme tiredness is one … what else?"

"Phenergan can cause sedation or slight euphoria (aka dopamine). It is not surprising that it messes with your focus and energy level."

Why Some People Dislike It Despite Its Benefits

Even when Phenergan does help nausea or other symptoms, side effects often make people hesitant to continue it regularly.

"It was an absolute game changer. I still have a very small list of safe foods, but I went four days without vomiting and I was so much more functional despite it making me feel like a complete zombie."

What Medical Sources Say – How Reddit Lines Up

According to NHS and other official sources, common side effects include:

  • Daytime tiredness / drowsiness (NHS)
  • Dizziness or unsteadiness (NHS)
  • Nightmares, especially in children (NHS)
  • Blurred vision (Medicines.org.au)
  • Dry mouth, throat & nose (NPS.org.au)
  • Gastrointestinal upset (nausea, constipation, or diarrhea) (NPS.org.au)

Many Reddit reports mirror these, but some describe more intense or prolonged effects (e.g. very long drowsiness, vivid/disturbing dreams, GI burning/cramps) that may not always be highlighted in official warnings.

Final Thoughts: What to Expect & Manage

From what Redditors report, here are some takeaways if you or someone you know is starting Phenergan or uses it regularly:

  • Expect drowsiness. It can be heavy and last well into the next day.
  • Use it when you can rest; plan around times you need to be alert.
  • Watch for digestive irritation, especially with suppository forms or when stopping/starting.
  • Mental side effects (nightmares, restlessness, vivid dreams) seem fairly common.
  • Tolerance may build — the sedative effects often lessen over time, though not everyone experiences that.
  • Always follow medical advice, especially with dosage, and consult a doctor if side effects are severe or unexpected.

This article summarises anecdotal Reddit experiences and should not replace medical guidance. Always consult a healthcare provider before starting or changing any medication.