A client is being discharged on oral iron supplements. Which instruction is most important to prevent the most common adverse effect?

ORAL IRON SUPPLEMENTATION TEACHING: MOST COMMON ADVERSE EFFECT: GI distress — nausea, constipation, stomach cramps; dark/black stools (expected, not a sign of GI bleeding unless bright red); MANAGING GI EFFECTS: Take with small amount of food to reduce nausea (reduces absorption slightly but improves adherence); increase fluid and fibre intake; stool softener may be ordered; start at lower dose and increase gradually; MAXIMISING ABSORPTION: Vitamin C (ascorbic acid) significantly increases iron absorption — orange juice, tomato juice, or vitamin C supplement with the dose; avoid coffee, tea, milk, calcium supplements, antacids within 2 hours (inhibit absorption); DIFFERENT FORMULATIONS: Ferrous sulphate (most common); ferrous gluconate (more expensive, gentler on GI); LIQUID FORM: Use a straw to prevent tooth staining; PATIENT EDUCATION: Expected black stools; expected mild GI upset initially; do not stop without notifying provider; takes 4-8 weeks to see improvement in fatigue/haemoglobin.