No. Oral tolerability does not establish inhaled tolerability. Delivering a substance to the airways changes the exposure and can introduce risks that are not apparent from oral-supplement research.
A small randomized crossover experiment found airway narrowing after nebulized glutathione in people with mild asthma. The study is limited in size and setting, but its result is enough to challenge the assumption that an antioxidant must be harmless when inhaled.
A helpful cellular role does not validate a route
A substance can participate in normal protective biology without being beneficial in every concentration, formulation or delivery setting. The relevant question is how the administered preparation affects the actual patient.
The route determines which tissues encounter the preparation first and under what conditions. That is why one route's evidence should not be used to authorize another. A shared ingredient name does not erase the difference.
An airway reaction also cannot be safely reclassified as productive clearing or detoxification on the basis of a sensation. Breathing symptoms require appropriate clinical interpretation.
What the study does and does not establish
The experiment does not quantify the risk for every person, every lung disease or every preparation. It should not be used to diagnose an individual reaction without assessment.
It also does not support a home strategy for preventing the reaction or modifying the preparation. An experimental comparison conducted under supervision is not an instruction manual for managing a complication.
A meaningful respiratory-treatment claim would require evidence in the relevant diagnosis, with outcomes such as function and symptoms assessed alongside harms. Research on blood antioxidant measures after swallowing a supplement cannot supply that evidence.
Someone with asthma or another respiratory condition should discuss treatment questions with their clinician and avoid replacing prescribed care with an unvalidated route. New breathing difficulty deserves prompt attention.
The central lesson is route specificity: natural occurrence, oral availability and mechanistic plausibility are not substitutes for clinical evidence about inhalation. That distinction is more useful than labeling glutathione globally safe or globally unsafe.