Minocycline is one of the listed drugs that cause vitamin B12 malabsorption.
Minocycline also has anti-thyroid effects.
Long term treatment with minocycline (at least 100 mg/day) can cause hyperpigmentation of the skin, nails, bones, thyroid, teeth, palate, eye, heart valves. Thyroid cancer is frequently found with black thyroid syndrome (macroscopic black discolouration of the thyroid gland).