Clinical practice has demonstrated that some drugs can reduce the efficacy of levodopa and some can increase its toxic side effects. In order to maintain better efficacy of levodopa and prevent toxic side effects, drugs that should not be applied simultaneously with levodopa include: (1) Vitamin B6: It is a coenzyme of dopa decarboxylase, which can strengthen the activity of peripheral dopa decarboxylase and accelerate the rate of dopa decarboxylation into dopamine outside the brain, while reducing the entry of levodopa into the brain and decreasing its efficacy. Therefore, the use of vitamin B6 and foods rich in vitamin B6 should be limited. However, the effect on compound levodopa is not significant. (2) Rifampin and its compound preparations (such as compound Rifampin tablets, Adafin, hypocretin, hypocretin, hypotensive static, hypotensive etc.) should be avoided because they can increase the depletion of dopamine in the terminal vesicles of dopamine neurons. In hypertensive patients without Parkinson’s disease, long-term, heavy medication can also cause Parkinson’s syndrome. (3) Valium and phenothiazines: they can antagonize the effect of levodopa and should be avoided as much as possible, including chlorpromazine, endorphin, fluphenazine, promethazine, etc. These drugs can cause Parkinson’s syndrome and postural hypotension, so they should not be used at the same time. (4) Non-selective monoamine oxidase inhibitors can impede the inactivation of dopamine and other catecholamines, causing the accumulation of dopamine in the blood, resulting in increased blood pressure and even hypertensive crisis and hyperthermia. Therefore, such drugs, such as eugenol, isocarbohydrazide, and phenelzine, should be discontinued at least 2 weeks prior to the use of levodopa. In contrast, B-type monoamine oxidase inhibitors (e.g., Sigfrancine or Kingspine at daily doses of 20 mg or less) generally do not cause elevated blood pressure. (5) Tricyclic antidepressants: such as amitriptyline, amoxapine and chlorpromazine can enhance the efficacy of levodopa, but can cause cardiac rhythm disturbance, especially in elderly patients who are more prone to it, and should be avoided.