The recommended adult dose of Tagrisso® is 80 mg taken by mouth once a day. If necessary, the dose may be reduced to 40 mg once a day.
It can be taken with or without food at the same time each day and should be swallowed whole with water. The tablet should not be crushed, split or chewed.
If unable to swallow the tablet, it may first be dispersed in 50 mL of non- carbonated water (room temperature). The tablet should be dropped in the water, without crushing, stirred until dispersed and immediately swallowed. An additional 50 mL of water should be added to ensure that no residue remains in the glass and then immediately swallowed. No other liquids should be added.

Osimertinib is a Tyrosine Kinase Inhibitor (TKI), and is an oral, potent, and selective irreversible inhibitor of both Epidermal Growth Factor Receptor (EGFR) sensitizing- mutations (EGFRm) and T790M resistance mutation (T790M) that has limited activity against wild-type EGFR.

Skin and nail problems can occur. You may get rash, dry skin, itching and problems with your nails. These are more likely in areas exposed to the sun. This can include paronychia which is red, hot, painful pus-filled blisters or swelling around the nail or an infection where the nail and skin meet at the side or the base of a fingernail or toenail. Consider using moisturizers regularly on your skin and nails to help control these problems.
Eye problems can occur. You should tell your doctor right away if you get any symptoms of eye problems: eye pain, swelling, redness with a gritty feeling, watery eyes; blurred vision, sensitivity to light, sudden changes in your eyesight, or other eyesight changes. If left untreated, your eye problems may worsen and may lead to loss of eyesight. You may be at increased risk if you wear contact lenses.
Driving and using machines: Do not drive or use any tools or machines if you feel dizzy or get any symptoms that affect your eyesight, ability to concentrate or react.
Side effects may include:

• Decrease in appetite, sores inside the mouth
• Vomiting
• Headache, dizziness, decreased ability to concentrate or react
• Weakness, feeling tired
• Back pain
• Cough
• Nose or throat infection, runny or stuffy nose
• Nose bleeds
• Changes in eyesight

Do not use if you are allergic to osimertinib.
Use with caution if you:

• have suffered from interstitial lung disease (including pneumonitis) which means that your lungs were inflamed or scarred.
• have ever had heart problems.
• have liver disease or kidney disease.
• have a history of eye problems

Effective birth control must be used during treatment as osimertinib can cause miscarriage and birth defects.  Men must use a condom because the drug may pass into the sperm.  After finishing treatment with osimertinib women must keep using birth control for at least 2 months and men for at least 4 months.
This medication may change how well some birth control methods work including birth control pills. Talk to your doctor about the most appropriate methods of birth control. You may need to add a barrier method to your birth control.

Osimertinib should not be taken if breastfeeding.

The following medications may reduce how well osimertinib works:

•  Phenytoin, carbamazepine or phenobarbital.
•  Rifabutin or rifampicin.
•  St. John’s Wor

Osimertinib may reduce effectiveness of the following medications:

• Warfarin 
• Pimozide 
• Tizanidine 
• 'Statin’ medicines 
• Oral hormonal birth control pill 
• Phenytoin 
• Alfentanil, fentanyl and other painkillers 
• Ciclosporin, sirolimus and tacrolimus
• Daunorubicin, doxorubicin, paclitaxel and topotecan 
• Migraine medicines called ‘ergot alkaloids’ 
• Quinidine, digoxin, disopyramide, amiodarone, sotalol, dofetilide, ibutilide, verapamil and diltiazem, procainamide, dronedarone, flecainide, propafenone 
• Loop, thiazide and related diuretics; laxatives and enemas; amphotericin B and high-dosecorticosteroids