supplement timing
20 interactions related to supplement timing
levothyroxine + magnesium
Taking magnesium too close to levothyroxine can modestly reduce how much of the thyroid medicine is absorbed, because magnesium can bind levothyroxine in the gut.
antibiotics + calcium
Calcium can bind to certain antibiotics (tetracyclines and fluoroquinolones) in the gut and reduce how much of the drug is absorbed.
levothyroxine + iron
When taken at the same time, iron can reduce how much levothyroxine your body absorbs by forming a poorly soluble complex in the gut, which can blunt the effect of your thyroid medication and raise TSH.
omega-3 + vitamin d
Fat from omega-3 supports absorption of the fat-soluble vitamin D
vitamin d + magnesium
Magnesium helps activate and support the function of vitamin D; low magnesium can reduce the effectiveness of vitamin D supplementation. This is a beneficial nutrient synergy rather than a harmful interaction.
antibiotics + probiotics
Taken at the same moment, an antibiotic can kill bacterial probiotic organisms before they reach the gut, lowering the probiotic's benefit. Spacing the doses apart fixes it.
doxycycline + iron
Iron forms an insoluble chelate complex with doxycycline in the gut, sharply reducing absorption of the antibiotic. In controlled human studies, ferrous sulfate taken together with doxycycline cut serum antibiotic levels substantially, which can undermine treatment.
curcumin + piperine
Piperine (black pepper extract) substantially increases how much curcumin your body absorbs.
doxycycline + magnesium
Magnesium ions can bind doxycycline in the gastrointestinal tract, forming a poorly absorbed complex that reduces how much antibiotic reaches the bloodstream. Magnesium-containing supplements, antacids, and laxatives can meaningfully lower doxycycline absorption if taken at the same time.
levothyroxine + calcium
Calcium can reduce levothyroxine absorption when the two are taken close together
metformin + vitamin b12
Long-term metformin use can reduce vitamin B12 absorption, sometimes enough to cause deficiency.
doxycycline + calcium
Calcium binds doxycycline in the gut, forming a complex the body cannot fully absorb. Taking doxycycline together with calcium supplements, calcium-based antacids, or large dairy servings can lower how much antibiotic reaches the bloodstream, though doxycycline binds calcium less than older tetracyclines.
vitamin c + iron
Vitamin c enhances absorption of non-heme iron from supplements and plant foods, a beneficial nutrient synergy, though the real-world benefit across a full diet is usually modest.
calcium + iron
Calcium can reduce the absorption of iron when the two are taken together, with the effect most pronounced for non-heme iron from supplements and plant foods.
iron + zinc
High-dose iron and zinc supplements can compete for absorption in the small intestine when taken together, especially in solution on an empty stomach, potentially reducing the effectiveness of one or both minerals. The competition is minimal when the minerals are taken with food or hours apart, or at ordinary dietary amounts.
tetracycline + zinc
Zinc forms a chelate with tetracycline in the gastrointestinal tract, modestly reducing absorption of the antibiotic. The interaction also reduces zinc absorption. Doxycycline is much less affected.
tetracycline + calcium
Calcium binds to tetracycline in the gut, forming an insoluble chelate that the intestine cannot absorb. Dairy products, calcium supplements, and calcium-based antacids can sharply reduce how much tetracycline reaches your bloodstream, which can drop levels below what is needed to treat the infection.
creatine + carbohydrates
Taking creatine together with carbohydrate raises insulin, which increases how much creatine skeletal muscle retains by stimulating the sodium-dependent creatine transporter. The effect mainly speeds up the loading phase; long-term muscle saturation is reached either way with daily consistency.
levofloxacin + calcium
Calcium binds (chelates) levofloxacin in the gastrointestinal tract, modestly lowering the antibiotic's peak blood level. Total drug exposure over the dosing interval is largely preserved, so the effect is smaller than with iron, magnesium, or aluminum. Separating the doses by a couple of hours avoids the interaction.
magnesium + zinc
At high supplemental doses, zinc and magnesium can each modestly reduce the other's absorption in the gut — and the better-documented direction is zinc lowering magnesium absorption, not the reverse. The effect is minor and dose-dependent; ordinary multivitamin amounts rarely matter.