Supplements for people on metformin

The metformin-companion stack — rationale by ingredient

Vitamin B12 (methylcobalamin or hydroxocobalamin) — the non-negotiable one

Metformin reduces B12 absorption via interference with calcium-dependent terminal-ileum uptake. The 2024 ADA Standards of Care recommend periodic B12 monitoring in long-term metformin users, especially those with anaemia or neuropathy. Test serum B12 (and methylmalonic acid if borderline) every 1–2 years. Supplement at 500–1000 mcg/day if low or borderline. The B12 depletion effect is dose- and duration-dependent — patients on >1500 mg/day for >5 years are higher-risk.

Magnesium glycinate 300–400 mg elemental nightly

Low magnesium status is more common in type 2 diabetes and is associated with worse insulin sensitivity. The 2025 meta-analysis on magnesium and glycaemic control suggests modest improvement in HbA1c with supplementation in deficient patients. The glycinate form is the most GI-friendly. Particularly useful at night for sleep and muscle cramps.

CoQ10 (ubiquinol) 100–200 mg/day

Modest evidence that metformin reduces CoQ10 levels via mitochondrial-complex-I effects, though smaller than the statin effect. Worth considering in patients on metformin + statin combination or with documented exercise intolerance. Take with a fat-containing meal for absorption.

Omega-3 EPA/DHA 1.5–2 g/day

Foundational cardiovascular adjunct in diabetes. Reduces triglycerides and supports overall lipid management. Pair with a real cardiovascular care plan.

Vitamin D3 to a 25-OH-D of 30–50 ng/mL

Deficiency is more common in type 2 diabetes cohorts. Test first; supplement to the normal range. Routine high-dose empirical dosing is not appropriate.

Psyllium husk 5–10 g/day

Soluble fibre with FDA cholesterol claim and modest glycaemic effect (reduces postprandial glucose excursions). Take separately from metformin and other medications by 1–2 hours to avoid binding interactions.

Alpha-lipoic acid 600 mg/day (if neuropathy)

Best-evidenced supplement for diabetic peripheral neuropathy. Modest improvement in nerve-conduction studies and patient-reported pain at 600 mg/day. Use only if you have neuropathic symptoms; not a routine prophylactic.