Herb & supplement monograph

Fish Oil Drug Interactions, Uses, Effectiveness, Safety & More

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS ·Updated July 2026

What is this page for?

First and foremost: how Fish Oil interacts with medications. The heart of this page is the interaction list — every drug Fish Oil is known to interact with, and how serious each one is.

But these pages have grown well beyond that into a full monograph — what Fish Oil is, what people use it for and how strong the evidence is, its safety and side effects, and answers to the questions we’re asked most — written and reviewed by the clinical staff at HelloPharmacist. It’s educational information from our licensed clinical databases, not medical advice, and we don’t sell or endorse products. Our editorial policy

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Fish Oil Drug Interactions: The Bottom Line

From the HelloPharmacist Editorial Team · Updated July 2026

Based on the available evidence, the overall risk of a clinically significant Fish Oil drug interaction appears low for most people. None of the listed interactions are rated major, and the best-documented concerns mostly apply to a small group of closely monitored medicines.

Interactions deserving the most attention

The strongest human evidence involves the transplant drugs sirolimus, tacrolimus, and cyclosporine, where fish oil raised blood levels of these narrow-margin medicines, in one study enough that the sirolimus dose had to be reduced. Fish oil can also modestly lower blood pressure, so it may add to the effect of blood pressure medications. With warfarin and other blood thinners, the evidence conflicts: a few case reports suggest a bleeding risk, but studies have not shown a meaningful change in most people.

What the rest of the list means

A long interaction list does not mean every combination is harmful. Many entries are theoretical, based on possible effects on how the body absorbs fats or processes medications, and several predicted effects have not produced meaningful changes in people. Fish oil's mild effects on blood pressure and platelets tend to matter only when a medicine leaves little room for error.

Check your medications against Fish Oil

Based on HelloPharmacist’s Fish Oil interaction data and reviewed under our editorial standards.

Interaction report

Drugs that interact with Fish Oil

327 medications have a known interaction with Fish Oil, graded by severity. Select any drug for the full evidence-based detail.

Don’t want to scroll the list? Just ask.

Tell us the medications you take and we’ll check each one against Fish Oil using our pharmacist-reviewed interaction data.

AI summaries are generated from our Fish Oil interaction data for education only — always confirm with your pharmacist. How we use AI

2,830 drugs

Read The List Like a Pharmacist

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Major. Clinically significant; generally best avoided, or used only under direct professional supervision.
Moderate. May need monitoring, a dose adjustment, or separating the times you take each one.
Minor. Generally not clinically significant, but still worth noting and mentioning to your pharmacist.
No known interaction. Checked against our sources with nothing documented — not the same as proven safety.

Likelihood — How Well It’s Documented

Likely. Well-controlled human studies have demonstrated the likely existence of this interaction
Probable. Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
Possible. Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists
Unlikely. Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans.

Where This Data Comes From

Interaction records are evidence-graded and sourced from the Natural Medicines database (TRC Healthcare), the same reference used by pharmacists and hospitals.
Each drug listed above links to the full report for that exact Fish Oil combination — clinical detail, likelihood, evidence level, and citations.
Content is reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

The big picture

The kinds of drugs Fish Oil affects

Every type of medication (drug category) Fish Oil is known to interact with. Open any category for the detail — or search your exact drug in the checker above.

All 9 drug categories Fish Oil interacts with

Antihypertensive DrugsContraceptive DrugsCyclosporine (neoral, Sandimmune)Orlistat (xenical, Alli)Sirolimus (rapamune)Tacrolimus (prograf)Anticoagulant/antiplatelet DrugsPlatinum AgentsWarfarin (coumadin)

Antihypertensive Drugs

Theoretically, taking fish oil with antihypertensive drugs might increase the risk of hypotension.
Clinical evidence indicates that fish oils can modestly lower blood pressure and might have additive effects in patients treated with antihypertensives.

Likelihood Probable Evidence B

Contraceptive Drugs

Theoretically, taking fish oil with contraceptive drugs might decrease the triglyceride-lowering effects of fish oil.
There is some evidence that contraceptive drugs might interfere with the triglyceride lowering effects of fish oils.

Likelihood Probable Evidence B

Cyclosporine (Neoral, Sandimmune)

Taking fish oil with cyclosporine might increase levels and adverse effects of cyclosporine.
In kidney transplant recipients on a general immunosuppressive regimen, taking omega-3 fatty acids daily seems to increase peak blood levels of cyclosporine when compared with placebo. This increase was as much as 20% after one month. However, the area under the curve was not significantly affected.

Likelihood Probable Evidence B

Orlistat (Xenical, Alli)

Theoretically, taking fish oil with orlistat might decrease the absorption of fish oil fatty acids.
Orlistat binds lipase in the gastrointestinal tract and reduces fat absorption. Theoretically, taking fish oil with orlistat might decrease absorption of fish oil fatty acids. To avoid this potential interaction, recommend separating administration of orlistat and fish oil by at least 2 hours.

Likelihood Probable Evidence D

Sirolimus (Rapamune)

Taking fish oil with sirolimus might increase levels and adverse effects of sirolimus.
Pharmacokinetic research shows that omega-3 fatty acids increase exposure to sirolimus in kidney transplant patients on a calcineurin inhibitor-free immunosuppressive regimen. A 25% dose reduction in sirolimus was required to keep patients within the expected trough-concentration window. Researchers hypothesize that this may be due to inhibition of cytochrome P450 3A4 (CYP3A4) by fish oil, although this has not been confirmed in clinical research.

Likelihood Probable Evidence B

Tacrolimus (Prograf)

Taking fish oil with tacrolimus might increase levels and adverse effects of tacrolimus.
In a small group of patients, taking fish oil 2.6 grams (Omacor) daily for 4 weeks increased the 8-hour area under the curve of tacrolimus by 25% when compared with baseline. Peak levels were increased by approximately 22%. Researchers hypothesize that this may be due either to an increase in bioavailability or to inhibition of cytochrome P450 3A4 (CYP3A4) by fish oil, although this has not been confirmed in clinical research.

Likelihood Probable Evidence B

Anticoagulant/Antiplatelet Drugs

Fish oil may have antiplatelet effects and may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs. However, evidence is conflicting.
While fish oil may not be a potent inhibitor of platelet function, high doses of fish oil might have antiplatelet effects. Theoretically, concomitant use of fish oil with anticoagulant or antiplatelet drugs may increase the risk of bleeding. However, the most rigorous research shows that short-term doses of fish oil 10 grams daily or long-term doses of 1.5 grams daily for up to 52 weeks does not increase the risk of bleeding or affect coagulation parameters in chronically ill and vulnerable patients. Other controlled research shows that fish oil does not affect platelet function or increase the risk of bleeding. Some research even suggests that perioperative fish oil use decreases bleeding risk. Some research suggests fish oil does not have additive antiplatelet effects when combined with aspirin, but other clinical evidence suggests that adding fish oil to low-dose aspirin treatment increases antiplatelet effects in patients who are aspirin-resistant. Also, some clinical research seems to show that fish oil has additive antiplatelet effects when used with aspirin and clopidogrel compared to aspirin and clopidogrel alone.

Likelihood Unlikely Evidence B

Platinum Agents

Theoretically, taking fish oil with platinum agents can cause resistance to platinum agents, potentially decreasing their effectiveness.
Platinum-induced fatty acids (PIFAs) are fatty acids secreted from human and mouse stem cells when exposed to platinum-based chemotherapy. Animal research suggests that PIFAs cause resistance to chemotherapy by stimulating lysophospholipid production in the spleen, which interferes with the DNA damage caused by certain chemotherapy drugs. One PIFA, known as 16:4(n-3), has been found in both raw fish and some commercially available fish oil products. Mackerel and herring have high PIFA concentrations, while salmon and tuna have low PIFA concentrations. Levels of PIFA in commercial fish oil products ranged from 0.2- 5.7 microMol. Animal research shows that PIFA-containing fish oil products cause resistance to cisplatin, fluorouracil, irinotecan, and oxaliplatin. It is unclear if all commercially available fish oil products contain PIFAs. Additionally, it is argued that levels of PIFA found in some fish oil products are too low to be of clinical concern. Furthermore, a lack of chemotherapy resistance in countries with high fish intake, such as Greenland, Japan, and Norway, suggest that this interaction may not be clinically significant.

Likelihood Unlikely Evidence D

Warfarin (Coumadin)

Fish oil may have antiplatelet effects and might increase the risk of bleeding if used with warfarin.
Fish oil has antiplatelet effects at high doses. Case reports show elevated INR in patients taking warfarin and fish oil 1-2 grams daily. However, some clinical research shows that taking fish oil 3-6 grams daily does not significantly increase INR in patients taking warfarin.

Likelihood Unlikely Evidence B

Monograph

Fish Oil: Uses, Safety & Side Effects

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Reviewed July 2026 ·

The bottom line

Fish oil provides omega-3 fatty acids (EPA and DHA) that are best known for lowering high triglyceride levels. The evidence for other heart and health benefits is mixed, and it is generally well tolerated. Talk with your pharmacist or doctor before starting it, especially if you take blood thinners or have a fish allergy.

Part used: Oil from fatty fish (such as mackerel, salmon, sardines, and anchovies)
Common forms: Softgel capsules, liquid, gummies, and fortified foods

People commonly use it for

High triglycerides
Heart health
Joint pain and inflammation
Brain and eye health
Dry eyes

Popular and traditional uses — not proof it works. See “Uses & effectiveness” below for the evidence.

Safety at a glance

OverallLikely safe

Fish oil is generally well tolerated for most adults at typical supplement doses.

PregnancyLikely Safe

When used orally and appropriately. Intake of fish oil during pregnancy does not appear to adversely affect the fetus or nursing infant. One large cli...

Read the full pregnancy detail

BreastfeedingLikely Safe

When used orally and appropriately. Intake of fish oil during pregnancy does not appear to adversely affect the fetus or nursing infant. One large cli...

Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center). Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

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Overview

Fish oil is a dietary supplement made from the tissues of oily fish such as mackerel, salmon, sardines, herring, and anchovies. It is a rich source of omega-3 fatty acids, mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

Omega-3 fatty acids are considered important for normal body function, including the heart, brain, and eyes. Because many people do not eat enough fatty fish, fish oil supplements are a popular way to add these fats to the diet.

Fish oil comes in capsules, liquids, gummies, and is sometimes added to fortified foods. There are also prescription versions of purified omega-3s used to treat very high triglyceride levels.

How it works

The active parts of fish oil are the omega-3 fatty acids EPA and DHA. The body uses these fats to build cell membranes and to make signaling molecules that help control inflammation.

Omega-3s are thought to lower triglycerides by reducing how much fat the liver makes and releases into the blood. They may also have mild effects on blood vessel function, heart rhythm, and the way platelets clump together.

Many of the proposed effects on inflammation come from laboratory and animal studies. While these mechanisms are biologically reasonable, they do not always translate into clear benefits in people.

Effectiveness

Does Fish Oil work?

Here’s what the research actually shows for each use — graded by Natural Medicines and reviewed by Dr. Brian Staiger, PharmD.

Evidence overview · 129 uses evaluated

1 Effective 10 Possibly effective 18 Leans ineffective 100 Insufficient evidence

How to read these evidence grades

Natural Medicines’ 7-point scale. We show each rating’s label word-for-word.

1EffectiveStrong, consistent evidence it works.

2Likely EffectiveGood evidence, though not yet conclusive.

3Possibly EffectiveSome evidence suggests a benefit.

4Possibly IneffectiveSome evidence it may not help.

5Likely IneffectiveFairly strong evidence it doesn’t help.

6IneffectiveStrong evidence it doesn’t work.

7Insufficient Reliable Evidence to RateToo little research to say either way.

Effective Hypertriglyceridemia