Can Hei Shun Pian and Ephedra be used interchangeably?
Generally speaking, Heishunpian (black顺片) and Ephedra (Ma Huang) are not interchangeable. Detailed analysis is as follows:

Heishunpian is hot in nature and pungent in taste. It functions to dispel cold, relieve pain, warm the middle jiao, and alleviate vomiting and counterflow qi. It is mainly used to treat pain caused by cold-damp obstruction, cold abdominal pain, and similar symptoms. Ma Huang is warm in nature and pungent in taste, with functions to induce perspiration, resolve exterior syndromes, ventilate the lungs, and relieve asthma. It is primarily used to treat wind-cold common cold and symptoms such as coughing and wheezing. As their therapeutic effects and targeted conditions differ, they should not be substituted for each other arbitrarily.
Additionally, Heishunpian contains certain toxic components, such as aconitine, and is contraindicated for pregnant women. Individuals with a heat constitution should also use it cautiously. Ma Huang may cause side effects such as palpitations, insomnia, and anxiety. Special populations, including pregnant women and patients with hypertension, should use it with caution. These contraindications further limit the interchangeability of these two herbs. When using Heishunpian and Ma Huang, formulations should be tailored according to the patient's specific condition and constitution, strictly following medical instructions.
During the treatment period, it is also advisable to avoid consuming raw, cold, greasy, spicy, or other irritating foods, to prevent compromising drug effectiveness or worsening physical discomfort.