Background and Objective: Theophylline has been used for decades in human medicine for its psychostimulant, anti-inflammatory, and bronchodilator effects. Historically, in pulmonary medicine, theophylline has been used in the treatment of obstructive pulmonary diseases such as bronchial asthma (BA) or chronic obstructive pulmonary disease (COPD). This review aims to determine whether theophylline still has its place in the therapy of obstructive pulmonary diseases or whether we can even extend its use to other diagnoses such as atropine-resistant cardiac arrests, apnea of prematurity, or others. Moreover, we also aim to determine if there is a rationale for using low-dose theophylline due to its immunomodulatory and anti-inflammatory effect, or if the future of methylxanthines lies in newly synthesized derivates of theophylline such as bamifylline, or doxofylline. Methods: The narrative review is based on a literature search of the articles indexed in the PubMed database in 2023. We searched the database since the year 2009 using the MeSH terms “theophylline”, “aminophylline”, and “methylxanthines” and we included original articles in the English language. Key Content and Findings: Theophylline has a number of adverse drug reactions (ADRs), the most serious of which is its effect on the cardiovascular system. It can cause severe arrhythmias or even cardiac arrest when overdosed. On the other hand, there is still a substantial amount of its applications in current clinical practice. Conclusions: There is considerable controversy associated with its use in current medicine, which can be attributed both to its narrow therapeutic range and its mentioned cardiotoxic effect. Herein, we summarize the current state-of-art of theophylline and its use in human medicine.