Drug & supplement interaction

K2/spice + Tadalafil

Tadalafil brand names: Cialis, Tadliq.

No Known Interaction

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Updated July 2026 · Pair last verified Sep 13, 2026

The bottom line No known interaction

We found no known interaction between K2/spice and Tadalafil 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. Additionally, although there is no interaction, the two are separately associated with some of the same side effects, which would make a new symptom harder to attribute to one or the other.

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Interaction report

K2/spice and Tadalafil

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 Tadalafil and K2/spice in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. 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.

K2/spice safety at a glance

K2/spice overall Avoid These products are illegal, unregulated, and have caused serious harm and death.

Pregnancy Avoid Never use during pregnancy; it can seriously harm both mother and baby.

Breastfeeding Avoid Avoid while breastfeeding; chemicals can pass to the infant and cause harm.

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

Still wondering about combining Tadalafil and K2/spice? Ask Dr. Brian Staiger, PharmD, BCPS directly ›

How we checked

Why No Interaction Is Listed for Tadalafil

Interactions in our licensed database are recorded against drug classes, not just single drug names. Tadalafil is filed under 5 classifications — including phosphodiesterase-5 inhibitors, vasodilators, cytochrome p450 3a4 (cyp3a4) substrates. K2/spice has documented interactions with 2 drug classes — the most serious being anticonvulsants (moderate) and qt interval-prolonging drugs (moderate) — and none of Tadalafil’s classifications are among them.

Classification data comes from our licensed Natural Medicines dataset. A medication can belong to classes beyond those recorded there, so this describes how the check was run — it is not a safety guarantee.

Keep it in perspective

K2/spice Does Interact With Other Medications

K2/spice has 208 moderate known drug interactions in our database — Tadalafil isn’t one of them. If you take anything else, check it against the full list below.

Moderate 208 No known interaction 2,622 (incl. Tadalafil)

Taking anything else?

Check Another of Your Medications Against K2/spice

Covers the 2,830 medications we’ve checked against K2/spice. Pick one to open its full report.

What to actually watch for

No Interaction Found — But Data Suggests K2/spice and Tadalafil May Share a Side Effect

This is not an interaction. Neither one changes how your body handles the other, and nothing here says they react together. What our sources do show is that each has separately been linked to the effects below — so taking both can make those effects more likely to turn up, and harder to pin on one or the other if they do.

Stomach pain Additional detail
K2/spice
“When inhaled, K2/spice can cause nausea, vomiting, abdominal pain, and diarrhea. In a review of United States poison control center reports, vomiting occurred in around 16% of K2/spice toxicity cases. An analysis of online forum posts from K2/spice users suggests that around 5% of users experience nausea and/or vomiting.”

K2/spice · Natural Medicines adverse-effect record, reported in diarrhea.
5 sources cited

99616. Lamy FR, Daniulaityte R, Nahhas RW, et al. Increases in synthetic cannabinoids-related harms: results from a longitudinal web-based content analysis. Int J Drug Policy. 2017;44:121-9. PubMed

99617. Law R, Schier J, Martin C, Chang A, Wolkin A; Centers for Disease Control (CDC). Notes from the field: increase in reported adverse health effects related to synthetic cannabinoid use - United States, January-May 2015. MMWR Morb Mortal Wkly Rep 2015;64(22

99624. Tait RJ, Caldicott D, Mountain D, Hill SL, Lenton S. A systematic review of adverse events arising from the use of synthetic cannabinoids and their associated treatment. Clin Toxicol (Phila) 2016;54(1):1-13. PubMed

108487. Ruiz-Maldonado TM, Dorey A, Christensen ED, Campbell KA. Near-fatal spice intoxication of a toddler. Pediatrics. 2021 Aug;148(2):e2021050888. PubMed

111236. D'Errico S, Zanon M, Radaelli D, et al. Acute Kidney Injury (AKI) in Young Synthetic Cannabinoids Abusers. Biomedicines 2022;10(8):1936. PubMed
Tadalafil

Listed in the ADVERSE REACTIONS section of the FDA label for Tadalafil. Read the label on DailyMed ›

Reported for K2/spice but not commonly for Tadalafil: heart failure, confusion, a heart attack and memory problems.

Effects for Tadalafil come from the ADVERSE REACTIONS section of its FDA label; effects for K2/spice come from the Natural Medicines adverse-effect record, quoted above. Where a percentage is shown, it is the share of 98,103 voluntary FDA FAERS reports for Tadalafil that mention that effect — a reporting proportion, not an incidence rate and not evidence the drug caused it. Wording is matched across sources by our own clinical vocabulary, so treat this as a prompt to pay attention, not a diagnosis.

From our Q&A

Questions About K2/spice or Tadalafil

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers K2/spice or Tadalafil, 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 Tadalafil

This page covers K2/spice only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Tadalafil page lists 144 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), American Mistletoe (major), Grapefruit (major), Hawthorn (major) and St. John's Wort (major).

By severity: 5 major · 98 moderate · 41 minor.

From our pharmacist’s overview on the Tadalafil page

“Grapefruit juice is the first thing to know about if you take tadalafil (Cialis, Tadliq). It blocks CYP3A4, the enzyme that clears the drug, so blood levels climb and side effects like a steep drop in blood pressure become more likely.”

Reviewed by 2 · Jul 18, 2026

Open the Tadalafil interaction page

How much people look this up

Where K2/spice and Tadalafil 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 K2/spice

Steady interest

#1,337 of 1,452 supplements looked up here in the last 7 days

29 days ago today

Medication Tadalafil

Top 1%

#16 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 K2/spice reference on this page ↓
Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The K2/spice and Tadalafil records this page draws on were last updated July 10, 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 Dr. Brian Staiger, PharmD, BCPS.

Supplement

About K2/spice

What is K2/spice?

Recreational drug ('legal high')
Marijuana substitute
Mood or perception changes
Sometimes used to avoid drug testing

K2/Spice is NOT a herbal supplement — it is plant material sprayed with man-made synthetic cannabinoid chemicals. It is dangerous, unpredictable, and has caused seizures, heart problems, psychosis, and deaths, so it should not be used.

Not a plant part; synthetic chemicals sprayed onto dried plant material · Dried plant material that is smoked or vaped; sometimes sold as liquid for vaping

An interaction check asks whether these two react with each other — it does not ask whether K2/spice is a good idea for someone in your situation. Here is what our K2/spice record says about it on its own.

K2/spice: dosing

There is no safe or recommended dose of K2/Spice. Because these are unregulated, illegal products with unknown and constantly changing ingredients, no dose can be considered safe. The strength can vary wildly even within a single package.This is not a supplement that should be taken at any amount. If you are looking for help with substance use, please reach out to a healthcare provider, pharmacist, or a substance-use support service.

From our K2/spice monograph — the full record covers uses, side effects and every documented interaction.

Read the full K2/spice monograph & all interactions

Medication

About Tadalafil

What Is Tadalafil Used For?

Brand names: Cialis, Tadliq

Tadalafil tablets (including Cialis and generic tadalafil) are used to treat erectile dysfunction (ED), the symptoms of benign prostatic hyperplasia (BPH — an enlarged prostate), or both conditions together. When used with the drug finasteride to start BPH treatment, this combination is recommended for up to 26 weeks.

Adcirca, Alyq (tablets), and Tadliq (oral suspension) are indicated specifically for pulmonary arterial hypertension (PAH — high blood pressure in the lungs), to improve the ability to exercise.

Most-Reported Side Effects for Tadalafil

From FAERS, the FDA’s public side-effect reporting system (99,210 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Dyspnea 11,917 reports

Headache 10,982 reports

Diarrhea 8,020 reports

Nausea 6,697 reports

Fatigue 6,080 reports

See full Tadalafil drug information

Keep checking

Other Drugs & K2/spice

Browse every other medication we’ve checked against K2/spice — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major

208Moderate

0Minor

2,621No known interaction

208 Moderate 2,621 No interaction

Moderate

208 interactions

Showing 60 of 208 moderate interactions — see all 208 on the K2/spice page.

No interaction 2,621 drugs checked — show the list

We also checked K2/spice against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,621 medications checked with no known interaction — see the full K2/spice list.

See the full K2/spice interactions page

See every supplement checked against Tadalafil, ranked by severity

Evidence & sources

K2/spice References

The 40 references that drive our K2/spice 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.

Amar JY, Ruta J, Rahimian D, Dillinger RL, Katz P. Toxic leukoencephalopathy with extrapyramidal dysfunction due to synthetic cannabinoids. J Clin Neurosci 2018;58:213-4. PubMed
Andonian DO, Seaman SR, Josephson EB. Profound hypotension and bradycardia in the setting of synthetic cannabinoid intoxication - a case series. Am J Emerg Med 2017;35(6):940.e5-940.e6. PubMed
McIlroy G, Ford L, Khan JM. Acute myocardial infarction, associated with the use of a synthetic adamantyl-cannabinoid: a case report. BMC Pharmacol Toxicol 2016;17:2. PubMed
Chinnadurai T, Shrestha S, Ayinla R. A curious case of inhalation fever caused by synthetic cannabinoid. Am J Case Rep 2016;17:379-83. PubMed
Clark BC, Georgekutty J, Berul CI. Myocardial ischemia secondary to synthetic cannabinoid (K2) use in pediatric patients. J Pediatr 2015;167(3):757-61.e1. PubMed
Davidson C, Opacka-Juffry J, Arevalo-Martin A, Garcia-Ovejero D, Molina-Holgado E, Molina-Holgado F. Spicing up pharmacology: a review of synthetic cannabinoids from structure to adverse events. Adv Pharmacol 2017;80:135-68. PubMed
Durand D, Delgado LL, de la Parra-Pellot DM, Nichols-Vinueza D. Psychosis and severe rhabdomyolysis associated with synthetic cannabinoid use: a case report. Clin Schizophr Relat Psychoses 2015;8(4):205-8. DOI
Freeman MJ, Rose DZ, Myers MA, Gooch CL, Bozeman AC, Burgin WS. Ischemic stroke after use of the synthetic marijuana "spice". Neurology 2013;81(24):2090-3. PubMed
Kelkar AH, Smith NA, Martial A, Moole H, Tarantino MD, Roberts JC. An outbreak of synthetic cannabinoid-associated coagulopathy in Illinois. N Engl J Med 2018;379(13):1216-23. PubMed
Lamy FR, Daniulaityte R, Nahhas RW, et al. Increases in synthetic cannabinoids-related harms: results from a longitudinal web-based content analysis. Int J Drug Policy. 2017;44:121-9. PubMed
Law R, Schier J, Martin C, Chang A, Wolkin A; Centers for Disease Control (CDC). Notes from the field: increase in reported adverse health effects related to synthetic cannabinoid use - United States, January-May 2015. MMWR Morb Mortal Wkly Rep 2015;64(22
Castaneto MS, Gorelick DA, Desrosiers NA, Hartman RL, Pirard S, Huestis MA. Synthetic cannabinoids: epidemiology, pharmacodynamics, and clinical implications. Drug Alcohol Depend 2014;144:12-41. PubMed
Monte AA, Calello DP, Gerona RR, et al. Characteristics and treatment of patients with clinical illness due to synthetic cannabinoid inhalation reported by medical toxicologists: a ToxIC database study. J Med Toxicol 2017;13(2):146-52. PubMed
Öztürk E, Oral A, Özdemir M, Bambul N. Synthetic marijuana "K2" induced ITP. Platelets 2015;26(3):258-9. PubMed
Schwartz MD, Trecki J, Edison LA, Steck AR, Arnold JK, Gerona RR. A common source outbreak of severe delirium associated with exposure to the novel synthetic cannabinoid ADB-PINACA. J Emerg Med 2015;48(5):573-80. PubMed
Sheikh IA, Luksic M, Ferstenberg R, Culpepper-Morgan JA. Spice/K2 synthetic marijuana-induced toxic hepatitis treated with N-acetylcysteine. Am J Case Rep 2014;15:584-8. PubMed
Tait RJ, Caldicott D, Mountain D, Hill SL, Lenton S. A systematic review of adverse events arising from the use of synthetic cannabinoids and their associated treatment. Clin Toxicol (Phila) 2016;54(1):1-13. PubMed
Yamanoglu A, Celebi Yamanoglu NG, Evran T, Sogut O. How much can synthetic cannabinoid damage the heart? A case of cardiogenic shock following resistant ventricular fibrillation after synthetic cannabinoid use. J Clin Ultrasound 2018;46(9):605-9. PubMed
Zheng CY, Minniti CP, Chaitowitz MH. Sickle cell crisis complicated by synthetic cannabinoid abuse: a case report. Hemoglobin 2016;40(3):220-2. PubMed
Yamanoglu A, Cakmak S, Celebi Yamanoglu NG, Sogut O. A new side effect of synthetic cannabinoid use by the bucket (waterpipe) method: acute respiratory distress syndrome (ARDS). Turk J Emerg Med 2017;18(1):42-4. PubMed
Tse R, Kodur S, Squires B, Collins N. Sudden cardiac death complicating acute myocardial infarction following synthetic cannabinoid use. Intern Med J 2014;44(9):934-6. PubMed
Rianprakaisang T, Gerona R, Hendrickson RG. Commercial cannabidiol oil contaminated with the synthetic cannabinoid AB-FUBINACA given to a pediatric patient. Clin Toxicol (Phila). 2020;58(3):215-216. PubMed
Kourouni I, Mourad B, Khouli H, Shapiro JM, Mathew JP. Critical Illness Secondary to Synthetic Cannabinoid Ingestion. JAMA Netw Open. 2020;3(7):e208516. PubMed
Ahmed ST, Alam A, Hassan A, Kamal S, Mahmood M. Acute Liver Failure Caused by Synthetic Marijuana Use. Am J Ther. 2020. doi: 10.1097/MJT.0000000000001181. PubMed
Ahmed T, Khan A, See VY, Robinson S. Cardiac arrest associated with synthetic cannabinoid use and acquired prolonged QTc interval: A case report and review of literature. HeartRhythm Case Rep. 2020;6(5):283-286. PubMed
Cohen K, Mama Y, Rosca P, Pinhasov A, Weinstein A. Chronic Use of Synthetic Cannabinoids Is Associated With Impairment in Working Memory and Mental Flexibility. Front Psychiatry. 2020;11:602. PubMed
Godwin PO, Unterman S, Elfessi ZZ, Bhagat JD, Kolman K. Management of Rodenticide Poisoning Associated with Synthetic Cannabinoids. Fed Pract. 2019;36(5):237-241.
Parajuli P, Regmi MR, Lara-Garcia OE, Abu Limon I, Deckard A. Man vs. man-made marijuana: A case of drug-induced posterior reversible encephalopathy syndrome (PRES) due to K2, a synthetic cannabinoid (SCB). J Community Hosp Intern Med Perspect. 2020;10(4) DOI
Skryabin VY, Vinnikova MA. Psychotic Disorders in Patients Who Use Synthetic Cannabinoids. J Psychiatr Pract. 2019 Nov;25(6):485-490. PubMed
Yildiz SS, Sutasir MN, Sigirci S, et al. Acute effects of synthetic cannabinoids on ventricular repolarization parameters. Turk Kardiyol Dern Ars. 2019;47(5):384-390.
Martínez L, La Maida N, Papaseit E, et al. Acute pharmacological effects and oral fluid concentrations of the synthetic cannabinoids JWH-122 and JWH-210 in humans after self-administration: an observational study. Front Pharmacol. 2021 Aug 19;12:705643. PubMed
Simon G, Tóth D, Heckmann V, Kuzma M, Mayer M. Lethal case of myocardial ischemia following overdose of the synthetic cannabinoid ADB-FUBINACA. Leg Med (Tokyo). 2022 Feb;54:102004. PubMed
Stogner J, Patterson C. Suicidal ideation, planning, and attempts among synthetic cannabinoid users across different demographic subgroups. Crisis. 2022;43(4):323-330. PubMed
Manini AF, Krotulski AJ, Schimmel J, et al. Respiratory failure in confirmed synthetic cannabinoid overdose. Clin Toxicol (Phila). 2022;60(4):524-526. PubMed
Theunissen EL, Reckweg JT, Hutten NRPW, et al. Intoxication by a synthetic cannabinoid (JWH-018) causes cognitive and psychomotor impairment in recreational cannabis users. Pharmacol Biochem Behav. 2021 Mar;202:173118. PubMed
Ruiz-Maldonado TM, Dorey A, Christensen ED, Campbell KA. Near-fatal spice intoxication of a toddler. Pediatrics. 2021 Aug;148(2):e2021050888. PubMed
D'Errico S, Zanon M, Radaelli D, et al. Acute Kidney Injury (AKI) in Young Synthetic Cannabinoids Abusers. Biomedicines 2022;10(8):1936. PubMed
Fatmi SS, Outlaw A. Coronary Vasospasm Associated With Synthetic Marijuana Resulting in Transient Electrocardiogram Changes and Troponin Elevation. Cureus 2022;14(5):e25084. PubMed
Gala Z, Kravchenko T, Volk L, Chatani P, Kar R, Choron RL. Subcutaneous Emphysema, Pneumothorax, Pneumomediastinum, and Pneumoperitoneum Following Synthetic Cannabinoid Toxicity in an Incarcerated Man. Am Surg 2022. PubMed
Jafry AH, LaGrow A, Akhtar KH, et al. Synthetic cannabinoids and ST elevation myocardial infarction. Am J Med Sci 2022;364(4):481-491. 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

Taking K2/spice and Tadalafil Together: Common Questions

Is it safe to take K2/spice with Tadalafil?

We do not list a known interaction between K2/spice and Tadalafil. 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.

Do K2/spice and Tadalafil have any of the same side effects?

Yes — our sources link each of them separately to one of the same effects. That is not an interaction: neither changes how your body handles the other. It does mean that if one of those effects turns up, it can be harder to tell which one is behind it. They are listed on this page with the source behind each.

How was the K2/spice and Tadalafil combination checked?

Interactions in our licensed database are recorded against drug classes. Tadalafil is filed under 5 classifications, and K2/spice has documented interactions with 2 drug classes — none of Tadalafil's classifications are among them. A medication can belong to classes beyond those recorded in our dataset, so this describes how the check was run rather than guaranteeing safety.

Does K2/spice interact with any other medications?

Yes. K2/spice has 208 documented drug interactions in our database — Tadalafil is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.

Does Tadalafil interact with any supplements?

Yes. Tadalafil has documented interactions with 144 supplements in our database — K2/spice is not one of them. The Tadalafil 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

K2/spice monograph Uses, safety profile, and every drug interaction in one place Tadalafil drug information The full plain-English guide to this medication Tadalafil supplement interactions Every supplement checked against Tadalafil, 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 40 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Tadalafil and K2/spice?

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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.