Smell in COVID-19 and Efficacy of Nasal Theophylline (SCENT 3)

Inclusion Criteria: * Participants will be recruited based on the following inclusion criteria: 1. males and females ages 18 to 75 years 2. located within or willing to travel to the state of Missouri or Illinois 3. Olfactory dysfunction that has persisted for \>3 months following suspected COVID-19 infection 4. Baseline University of Pennsylvania Smell Identification Test (UPSIT) consistent with decreased olfactory function (\<= 34 in women, \<=33 in men). This test is a clinically validated 40-question forced-choice odor identification test where microencapsulated odorants on a strip are released by scratching.70 This will determine that patients have both subjectively and objectively diagnosed OD prior to undergoing treatment. 5. Ability to read, write, and understand English and have access to email. Exclusion Criteria: * Individuals will not be allowed to participate in this study if they meet one or more of the following exclusion criteria: 1. History of olfactory dysfunction prior to COVID-19 infection 2. Any use of concomitant therapies specifically for the treatment of olfactory dysfunction 3. Use of or participation in previous trials of intranasal theophylline. 4. Known existence of nasal polyps, prior sinonasal, or anterior skull-based surgery 5. Dependence on theophylline for comorbid conditions such as asthma and chronic obstructive pulmonary disease (COPD) 6. History of an allergic reaction to theophylline or other methylxanthines 7. History of neurodegenerative disease (ie. Alzheimer's dementia, Parkinson's disease, Lewy body dementia, frontotemporal dementia) 8. Pregnant or breastfeeding mothers. 9. Current use of medications with significant (≥40%) interactions with theophylline, which include cimetidine, ciprofloxacin, disulfiram, enoxacin, fluvoxamine, interferon- alpha, lithium, mexiletine, phenytoin, propafenone, propranolol, tacrine, thiabendazole, ticlopidine, and troleandomycin.