Drug & supplement interaction

Slimfast Diet + Promethazine

Promethazine brand name: Phenergan.

No Known Interaction
Medically reviewed by · Updated June 2026 · Pair last verified Sep 20, 2026
The bottom line No known interaction

We found no known interaction between Slimfast Diet and Promethazine in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first.

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Interaction report

Slimfast Diet and Promethazine

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Promethazine and Slimfast Diet in our sources. This does not guarantee that the combination is completely free of risk — research on Slimfast Diet alongside specific medications may be limited.

Worth understanding: our licensed dataset holds no drug-interaction record for Slimfast Diet at all — not against Promethazine, and not against any other medication we track. This verdict therefore rests on the absence of any recorded data, not on research that looked at this combination and found nothing. We cannot rule an interaction out.

Slimfast Diet is an eating pattern rather than something you take. Ask your pharmacist or doctor before changing how you eat while on a prescribed medicine: some medicines are dosed around meals, and a change in diet can change how they work. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Slimfast Diet safety at a glance

Slimfast Diet overall Use caution Generally well tolerated for healthy adults, but it is a food-based plan rather than a tested medicine and is not right for everyone.
Pregnancy Use caution Calorie-restricting diet plans are not recommended during pregnancy; speak with your doctor about nutrition needs.
Breastfeeding Use caution Restricting calories while breastfeeding may not be appropriate; check with your doctor before using a meal-replacement plan.

Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Promethazine and Slimfast Diet? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
What to actually watch for

What Promethazine’s Own FDA Label Lists

This is not an interaction — none of it involves Slimfast Diet. These are the most notable effects listed in the ADVERSE REACTIONS section of Promethazine’s own FDA label, for the medication by itself. Knowing the drug’s own list makes it easier to work out the likely cause if something new turns up while you follow Slimfast Diet and take the medicine. 10 of them are worth acting on rather than waiting out — marked below.

  • A slow heartbeat Worth acting on
  • Hallucinations Worth acting on
  • Yellowing of the skin or eyes Worth acting on
  • Wheezing Worth acting on
  • Confusion Worth acting on
  • Seizures Worth acting on
  • A low platelet count Worth acting on
  • Hives Worth acting on
  • A low white blood cell count Worth acting on
  • Bleeding or bruising Worth acting on

Showing the 10 most notable of 26 label-listed effects — ranked by how unusual each one is across medicines generally, with serious effects weighted up.

From the ADVERSE REACTIONS section of the FDA label for Promethazine. Read the label on DailyMed › Where a percentage is shown, it is the share of 22,361 voluntary FDA FAERS reports for Promethazine that mention that effect — a reporting proportion, not an incidence rate and not evidence the drug caused it. Slimfast Diet’s licensed record lists no adverse effects our clinical vocabulary could match, so there is no Slimfast Diet side to compare — that is a limit of the record, not a statement that Slimfast Diet has no side effects.

From our Q&A

Questions About Slimfast Diet or Promethazine

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Slimfast Diet or Promethazine, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Promethazine

This page covers Slimfast Diet only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Promethazine page lists 83 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Henbane (major), Scopolia (major), Alfalfa (moderate) and Angel's Trumpet (moderate).

By severity: 3 major · 57 moderate · 23 minor.

From our pharmacist’s overview on the Promethazine page

“Promethazine (Phenergan) is a phenothiazine antihistamine used for allergies, nausea, and motion sickness, and it is strongly anticholinergic on its own, causing dry mouth, blurred vision, drowsiness, and constipation. That is why the 83 supplements and herbs on this list deserve real attention, starting with the three rated major.”

Reviewed by 2 · Jul 18, 2026

Open the Promethazine interaction page

How much people look this up

Where Slimfast Diet and Promethazine Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Slimfast Diet
Steady interest

#1,206 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Promethazine
Steady interest

#1,448 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Where does our data come from?
  • Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Slimfast Diet reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 20, 2026. The Slimfast Diet and Promethazine records this page draws on were last updated June 22, 2026.
  • What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
Data structure & sourcing designed and verified by .
Eating pattern

About Slimfast Diet

What is Slimfast Diet?

  • Weight loss
  • Weight maintenance
  • Meal replacement
  • Calorie control
  • Convenient on-the-go nutrition

SlimFast is a commercial brand of meal-replacement shakes, bars, and snacks designed to help with weight loss by controlling daily calories. It is not an herb or single supplement, and while structured meal-replacement plans can help some people lose weight in the short term, long-term success depends on overall diet and lifestyle. Talk with your doctor or pharmacist before starting if you have a medical condition such as diabetes.

Not applicable (commercial meal-replacement product, not a plant) · Ready-to-drink shakes, shake powders, meal-replacement bars, and snack products

An interaction check asks whether these two react with each other — it does not ask whether Slimfast Diet is a good idea for someone in your situation. Here is what our Slimfast Diet record says about it on its own.

Slimfast Diet: dosing

There is no medicinal "dose" for SlimFast because it is a food product. Instead, follow the plan and serving sizes printed on the product label. A common approach is replacing one or two meals a day with a SlimFast shake or bar, eating one balanced meal, and having a small snack or two.Drink plenty of water and aim to keep your overall diet balanced.

From our Slimfast Diet monograph — the full record covers uses, side effects and every documented interaction.

Read the full Slimfast Diet monograph & all interactions
Medication

About Promethazine

What Is Promethazine Used For?

Brand name: Phenergan

Promethazine is used for a wide range of conditions. Tablets, oral solution, and rectal suppositories (brands including Phenergan, Promethegan, and Phenadoz) are approved for seasonal and perennial allergic rhinitis, vasomotor rhinitis, allergic conjunctivitis, hives (urticaria), angioedema, dermographism, and allergic reactions to blood or plasma. They are also used for motion sickness (both prevention and active treatment), nausea and vomiting related to anesthesia and surgery, sedation, and as a helper medication alongside pain relievers after surgery.

Promethazine hydrochloride injection (brands including Phenergan and Promethazine HCl injection) is used for many of the same purposes but is reserved for situations where oral treatment is not possible — including allergic emergencies as an adjunct to epinephrine, sedation during labor, and as an aid during certain surgical procedures such as bronchoscopy and eye surgery.

Most-Reported Side Effects for Promethazine

From FAERS, the FDA’s public side-effect reporting system (22,614 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Dependence 3,586 reports
Nausea 2,646 reports
Vomiting 1,802 reports
Fatigue 1,496 reports
Diarrhea 1,341 reports
See full Promethazine drug information
Keep checking

Other Drugs & Slimfast Diet

Browse every other medication we’ve checked against Slimfast Diet — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
0Moderate
0Minor
2,829No known interaction
2,829 No interaction
No interaction 2,829 drugs checked — show the list

We also checked Slimfast Diet against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,829 medications checked with no known interaction — see the full Slimfast Diet list.

See the full Slimfast Diet interactions page
See every supplement checked against Promethazine, ranked by severity
Evidence & sources

Slimfast Diet References

The 6 references that drive our Slimfast Diet monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

  1. Pritchett AM, Deswal A, Aguilar D, et al. Lifestyle Modification with Diet and Exercise in Obese Patients with Heart Failure - A Pilot Study. J Obes Weight Loss Ther. 2012 Mar 1;2(2):1-8. PubMed
  2. Berkowitz RI, Wadden TA, Gehrman CA, et al. Meal replacements in the treatment of adolescent obesity: a randomized controlled trial. Obesity (Silver Spring). 2011 Jun;19(6):1193-9. PubMed
  3. Morgan LM, Griffin BA, Millward DJ, et al. Comparison of the effects of four commercially available weight-loss programmes on lipid-based cardiovascular risk factors. Public Health Nutr. 2009 Jun;12(6):799-807. PubMed
  4. Truby H, Baic S, deLooy A, et al. Randomised controlled trial of four commercial weight loss programmes in the UK: initial findings from the BBC "diet trials." BMJ. 2006 Jun 3;332(7553):1309-14. PubMed
  5. Noakes M, Foster PR, Keogh JB, Clifton PM. Meal replacements are as effective as structured weight-loss diets for treating obesity in adults with features of metabolic syndrome. J Nutr. 2004 Aug;134(8):1894-9. PubMed
  6. Yip I, Go VL, DeShields S, et al. Liquid meal replacements and glycemic control in obese type 2 diabetes patients. Obes Res. 2001 Nov;9 Suppl 4:341S-347S. PubMed

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Following Slimfast Diet While Taking Promethazine: Common Questions

Is it safe to follow Slimfast Diet while taking Promethazine?
We do not list a known interaction between Slimfast Diet and Promethazine. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
Does Promethazine interact with any supplements?
Yes. Promethazine has documented interactions with 83 supplements in our database — Slimfast Diet is not one of them. The Promethazine interaction page linked on this page lists every one, ranked by severity.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Where next

Keep Exploring

Slimfast Diet monograph Uses, safety profile, and every drug interaction in one place Promethazine drug information The full plain-English guide to this medication Promethazine supplement interactions Every supplement checked against Promethazine, ranked by severity Supplement interaction checker Check any supplement or product against your medications Browse medications A–Z Every drug we’ve checked against herbs & supplements References The 6 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Promethazine and Slimfast Diet?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.