Dose: Adults: 10mg three times daily during the day, 3-4 hours, max 40mg/day. Geriatric patients may refer to adult dose. Patients with renal impairment: 2.5 mg three times daily, gradually increasing to a tolerable dose. Dosage: Dose approximately 3-4 hours apart – morning before waking, noon, afternoon (no later than 6PM). Avoid taking after dinner or four hours before bedtime. One hour after taking 10mg, standing systolic blood pressure may increase by 15-30mmHg. The effect may last for 2-3 hours. Do not lie in bed immediately after taking the drug. Side effects: >10% 1. Cardiovascular: Recumbent hypertension (7%-13%). 2, skin: erect hair (13%), itching (12%) 3, genitourinary: urinary urgency, urinary retention or polyuria, difficulty in urination (no more than 13%). 4. Neuromuscular and skeletal: abnormal sensation (18%) 1-10% 1. Central nervous system: chills (5%), pain (5%) 2, skin: rash (2%) 3. Gastrointestinal tract: abdominal pain. <1% Anxiety, mouth ulcers, confusion, dizziness, dry skin, erythema multiforme, facial flushing, headache, sensory allergy, insomnia, increased intracranial pressure, nausea, drowsiness, fatigue, dry mouth. Caution: 1. Use with caution in patients with diabetes mellitus and hepatic impairment; 2. Use with caution in patients with urinary retention and reduce initial dose; 3. Use with caution in patients with visual impairment, especially with concomitant hormone use; 4. Not recommended in patients with ambulatory hypertension, monitor liver and kidney function prior to and during treatment. Drug Interactions: 1. Beta-blockers: Enhance bradycardia effect (Risk C: monitoring required). 2.Calcium channel blockers: enhance the effect of bradycardia (Risk C: need to be monitored). 3, cardiac glycosides: to enhance the bradycardia effect (Risk C: need to be monitored). 4, cannabinoids: enhance the tachycardia effect of sympathomimetic drugs (Risk C: need to be monitored). 5.Iodobenzylguanidine I 123: sympathomimetic drugs may reduce the effect of iodobenzylguanidine I 123 (Risk X: avoid combination). 6.Monoamine oxidase inhibitors: enhance the hypertensive effect of α1 agonists (Risk X: avoid combination). 7, sympathomimetic drugs: enhance the toxic side effects of other sympathomimetic drugs (Risk C: need to monitor). 8, tricyclic antidepressants: strengthen the vasopressor effect of α1 agonists (Risk D: consider adjusting the medication).