If you are currently being treated with any of the following medications, you should not use flaxseed oil without first talking to your healthcare provider.

Blood-thinning Medications
Omega-3 fatty acids may increase the blood-thinning effects of warfarin, aspirin, or other blood-thinning medications. While the combination of aspirin and omega-3 fatty acids may actually be helpful under certain circumstances (such as heart disease), these medications should only be taken together under the guidance and supervision of your healthcare provider.

Cholesterol-lowering Medications
Following certain nutritional guidelines, including increasing the amount of omega-3 fatty acids in your diet and reducing the omega-6 to omega-3 ratio, may allow a group of cholesterol lowering medications known as "statins" (such as atorvastatin, lovastatin, and simvastatin) to work more effectively.

Cyclosporine
Taking omega-3 fatty acids during cyclosporine therapy may reduce toxic side effects (such as high blood pressure and kidney damage) associated with this medication in transplant patients.

Nonsteroidal Anti-inflammatory Drugs (NSAIDs)
In an animal study, treatment with omega-3 fatty acids reduced the risk of ulcers from nonsteroidal anti-inflammatory drugs (NSAIDs). More research is needed to evaluate whether omega-3 fatty acids would have the same effects in people.