No Clinically Significant Interactions Between These Supplements
Based on the available evidence, there are no clinically significant interactions between milk thistle (silymarin), magnesium glycinate, glycine, fish oil (omega-3 fatty acids), and vitamin D3 when taken together at standard supplemental doses.
Evidence Supporting Safety of This Combination
Milk Thistle Drug Interaction Profile
Milk thistle has a low likelihood of drug interactions and can safely be taken with most medications 1. The most robust human pharmacokinetic study demonstrated that 14 days of standardized milk thistle extract produced no significant influence on major cytochrome P450 enzymes (CYP1A2, CYP2C9, CYP2D6, or CYP3A4/5) 2. This is critical because it means milk thistle does not interfere with the metabolism of other substances through the liver's primary drug-processing pathways.
The safety profile is excellent: milk thistle is well tolerated even at high doses of 700 mg three times daily for 24 weeks, with only minor gastrointestinal effects like nausea or diarrhea reported 3. It has limited effect on the pharmacokinetics of several drugs in vivo despite some in vitro concerns 4.
Fish Oil and Vitamin D3 Combination
The combination of fish oil and vitamin D3 has been extensively studied together without safety concerns. The VITAL trial administered 460 mg EPA + 380 mg DHA plus 2000 IU vitamin D3 daily to 25,871 adults for 5.3 years with no reported interactions between these supplements 5, 6. Research specifically examining fish oil plus vitamin D3 supplementation found the combination well-tolerated and effective for metabolic outcomes 7.
Magnesium Glycinate with Vitamin D3
Combined magnesium (360 mg magnesium glycinate) and vitamin D3 (1000 IU) supplementation has been studied in randomized controlled trials without any reported adverse interactions 8, 9. In fact, magnesium serves as a cofactor in vitamin D metabolism, potentially enhancing vitamin D activation 9.
Glycine Safety
Glycine as an oral supplement has minimal adverse effects. The FDA drug label notes that adverse reactions primarily occur with large intravenous doses, not oral supplementation 10. Oral glycine does not interact with the other supplements in this combination.
Synergistic Benefits Without Interactions
Interestingly, some evidence suggests potential synergistic benefits rather than harmful interactions:
- Fish oil combined with silymarin (milk thistle) showed enhanced effects on lipid metabolism in animal models, reducing triglycerides by 45% and cholesterol by 18% 11
- Magnesium enhances vitamin D metabolism as a necessary cofactor, potentially improving vitamin D status more effectively than vitamin D alone 9
- The combination of fish oil and vitamin D3 showed cardiovascular benefits in large-scale trials 5
Practical Recommendations
Take all five supplements together without concern for interactions. Standard supplemental doses are:
- Milk thistle: 140-420 mg silymarin daily
- Magnesium glycinate: 200-400 mg elemental magnesium daily
- Glycine: 3-5 grams daily
- Fish oil: 1-3 grams EPA+DHA daily
- Vitamin D3: 1000-2000 IU daily (or as needed to maintain adequate 25OHD levels)
The only caveat: If you are taking medications with narrow therapeutic windows (like warfarin, certain chemotherapy agents, or immunosuppressants), consult your pharmacist about milk thistle specifically, though clinical evidence suggests minimal risk 3, 1.