5 Flaxseed Oil Side Effects and Best Dosage

Dosage Flax Oil While there are many health benefits, there are also some potential flaxseed oil negative effects. This page lists the main 5 side effects of flax oil  occasionally reported and suggests a dosage to reduce the chances of a negative reaction.

1. Blood Thinning Precautions

The omega-3 fatty acids in flax oil can help make blood platelets less sticky, potentially reducing the chances of a dangerous blood clot forming in our arteries.

This same effect though may amplify the action of blood thinning medications. It is very important to check with your doctor before taking flaxseed oil if you are using prescription drugs like warfarin, clopidogrel or even daily aspirin for blood thinning.

Supplementing at high doses with the oil may increase the risk of bleeding during or after surgery. It is recommended to stop taking flax, or any other omega-3 supplements, two weeks before undergoing major surgery.

2. Diabetes and Blood Sugar Levels

Taking large doses of flaxseed oil may slightly lower blood sugar levels. This would generally be a good thing, but there is some concern that diabetes sufferers taking blood sugar lowering medications at the same time as flax oil could reduce their blood sugar too low.

Once again, consult your doctor and avoid taking the oil at the same time as any important medications, regardless of the health condition.

3. Flaxseed Oil and Pregnancy

There are several reasons why flaxseed oil is more important for women, but it is not generally recommended for pregnant women in their second or third trimester.

This is due to some research suggesting a possible increase in the chance of a premature birth with large doses. While far from proven, it would be best to discuss this with your obstetrician or other healthcare professional before taking it during pregnancy.

Some medical resources also suggest not using flaxseed oil when breast-feeding, though no research is cited for this warning. Perhaps a corresponding warning for excessive amounts of omega-6 fats in the diet would be also be relevant for breastfeeding women.

4. Allergic Reactions 

Very occasionally, allergic reactions to flax oil have been reported that may include rashes, itching and swelling. These instances are considered very rare and have generally not been confirmed to actually be caused by flaxseed itself.

5. Gastrointestinal Problems

Gastrointestinal problems are sometimes associated with flax, though this is usually the high-fiber ground meal, rather than the extracted oil.

Occasionally an upset stomach and diarrhea has been reported with taking 30 grams or more in one dose of flaxseed oil. This is a large amount and probably too much to start with initially.

Below is a method for slowly increasing your dosage to get the maximum benefit while reducing the risk of side effects.

Best Flaxseed Oil Dosage

Flax is a powerful supplement and increasing your intake of omega-3 fatty acids and the other nutrients in it can have many health benefits. That said, some people do seem to react badly to large doses of flaxseed oil, especially if they have never had it before.

To minimize the chances of side effects, it is best to start off with the oil slowly and increase your daily dose on a weekly basis. Particularly if your diet has been lacking in omega-3 fats in the past, it will probably be more beneficial to increase your dosage steadily over several weeks, rather than immediately taking your maximum dose.

Taking flaxseed oil in this way gives your body time to adapt to a new omega-3 to omega-6 fat ratio, minimizing the risk of side effects. You can also monitor any positive results from taking the oil and get an idea of your ideal daily intake.

Having flaxseed oil with a meal is usually recommended over having it on an empty stomach. Splitting the dosage between morning and evening is also generally preferred, rather than having it all in one go.

It is also important to use a high-quality oil that is cold pressed and unrefined. There are several of the best of these listed in the page on where to buy flaxseed oil online.

With all this in mind, it can be a good idea to start your first week of flaxseed oil with just 1 gram in the morning with breakfast and 1 gram with your evening meal. This is only around a quarter of a teaspoon of the liquid oil or usually one capsule, but check the dosage information on the container.

For the following week this amount could be doubled to 4 grams a day. Split into 2 grams with breakfast or lunch and 2 grams with dinner. This is around half a teaspoon or two capsules.

By the third week you could double this again to a teaspoon or four capsules at around 4 grams per morning and 4 grams in the evening. 8 to 10 grams daily may be a good flaxseed oil dosage for most people.

If you wish to increase the amount taken beyond here it would be preferable to add to the total amount by just an extra gram per morning and evening for the subsequent weeks.

If you do experience any side effects from taking flaxseed oil you could either stop immediately and try again from the initial dose, or even just 1 grams a day.

Alternatively, you could cut the amount you take back by half or even a quarter and slowly built up by a gram a week to a level where you are seeing the health benefits without any side effects.

Some people report very positive results with 2 tablespoons a day of fresh flax oil. That’s around 30 grams. Others seem to have side effects with flaxseed oil at these larger amounts.

By starting a lower dosage and building up the amount of oil you take each week, your body is less likely to have a bad reaction to it. You may also find you are getting good results at 8 to 10 grams per day or even lower and don’t need to go up to the higher flaxseed oil dose.

Photo 1 credit with thanks: Healthaliciousness / Photo 2 credit with thanks: Acradenia


Click Here to Leave a Comment Below 10 comments

How about one takes 1 tbs. flaxseed 2-3 times per week? This person being on Warfarin, but, not taking at the same time as Warfarin and again, only having a tbs. a couple times per week, that should not be a problem, correct?

    Jim Dillan

    Hi Daniella,

    That doesn’t seem like a large amount as long as it is not taken anywhere near the medication. It’s still always advisable to consult your practitioner if you’re on important medications.


Do you have to take the oil separately or can you include it in meals and avoid treating it as a medicine?

    Jim Dillan

    Hi Jennifer,

    If you can add it to your meals that would be great but flaxseed oil shouldn’t be heated so on a salad is fine but in baked goods or a frying pan isn’t.

    Hope this helps.

James S. Kantor

I have been taking one tablespoon of Barlean’s Organic every day or sometimes every other day, for the last two years. Recently I started taking two tablespoons a day. When I start taking two tablespoon of flax-seed oil I notice an increase in clotting time say after I shave, in one week.

My family doctor said I could go back to my old dose but not to take two tablespoons a day.
I started taking two tablespoons after reading The Healing Power of Flax by Herb Joiner-Bey, ND which is a great book and highly recommend. I would just not take a high dose. I was mixing my flax oil in smoothies, but when I went to two, I was also taking directly by mouth. The recomendation from the book was one tablespoon per 100 pounds of weight.
I am a 55, yo white male, wt 200 lb in general good health. I do have hypertension and hypothyroidism, both treated.

    Jim Dillan

    Hi James and thanks for the information. Two tablespoons is quite high and a bit of a jump from one straight to two. I prefer to see doses go up more slowly, perhaps at a quarter of a tablespoon at a time, though it sounds best to take your doctor’s advice if he thinks it may interfere with medication.

    All the best.


My eye doctor said I should take flaxseed for dry eye. I bought Barlean’s 1200 mg capsules. Directions said 3-9 capsules. I took 3 capsules. Within 24 hours I developed itching all along my backside from upper thigh up to my waist. Wonder if taking 3 at once for my first time could result in this?

    Jim Dillan

    Hi there,

    It suggested to work up to the higher doses with flaxseed oil and 9 1000mg capsules would certainly be too much for some people to start. That you had such a reaction with 3 could mean you are a bit sensitive to them.

    I’d suggest starting with one a day with food for the first week. If this is well tolerated move up to 2 and so on. If you have a reaction move down in the dosage and then try again after a week.

    Hope this helps,



Is it better to take flaxseed oil with lignans or regular? Thanks.


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