Read the Patient Information Leaflet if available from your pharmacist before you start taking gefitinib and each time you get a refill. If you have any questions, ask your doctor or pharmacist.

Take gefitinib by mouth with or without food as directed by your doctor, usually once daily.

If you have trouble swallowing the tablet, you may place the tablet in a glass of water (4 to 8 ounces/120 to 240 milliliters). Stir well for 15 minutes. Drink all of the mixture right away. Rinse the cup with another 4 to 8 ounces (120 to 240 milliliters) of water and drink the rinse water to make sure you get the full dose.

Medications that reduce stomach acid (such as antacids, proton pump inhibitors/PPIs, H2 blockers) may make gefitinib work less well. If you take PPIs (such as lansoprazole, omeprazole), take gefitinib 12 hours before or 12 hours after taking the PPI. If you take antacids or H2 blockers (such as famotidine, nizatidine), take gefitinib 6 hours before or 6 hours after taking the antacid or H2 blocker.

The dosage is based on your medical condition, response to treatment, lab tests, and other medications you may be taking. Be sure to tell your doctor and pharmacist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

Use this medication regularly to get the most benefit from it. To help you remember, take it at the same time each day.

Do not increase your dose or use this drug more often or for longer than prescribed. Your condition will not improve any faster, and your risk of side effects will increase.