Promethazine should only be taken as prescribed by a healthcare professional. Consult your doctor or pharmacist for personalised instructions. The recommended adult dose for Promethazine to aid sleep is 25 to 50 milligrams taken orally at bedtime.  Follow these guidelines: Take the medication exactly as prescribed. Do not exceed the recommended dosage. Take promethazine shortly before bedtime to maximise its effects. Swallow tablets whole with water. Avoid alcohol and any other drugs with sedative properties while using Promethazine. Use promethazine for sleep when necessary and as prescribed. Short-term use is typically recommended.