Background The inadequate storage of biopharmaceuticals may result in an ineffective therapeutic response since poor conservation can lead to the emergence of protein aggregates and cause immunogenicity in patients, which can increase the risk of adverse events by inducing the production of anti-drug antibodies. This can also lead to significant economic losses for public health, given the high cost of these medicines. The aim of this study was to verify whether the home storage of biopharmaceuticals dispensed by the Unified Public System was in accordance with the manufacturers’ specified standards and whether external variables interfered with the correct home storage. Methods This was a prospective observational study. Patients with a confirmed diagnosis of rheumatoid arthritis, ankylosing spondylitis or psoriatic arthritis who were using a biologic exclusively dispensed by Unified Public System were included. Storage temperature was measured by digital thermometer inserted into the refrigerator of the participant’s home. Fisher’s exact test was performed to cross-reference the temperature data and the qualitative variables obtained using an epidemiologic questionnaire. Mean, minimum, maximum values and standard deviation were described in the quantitative data. Mann-Whitney non-parametric test was performed to the association between temperature excursion and the number of people in the house. Results A total of 81 participants were included and 67 (82.71%) did not maintain home storage correctly. The maximum temperature observed among all patients was 15.5 °C, the minimum was − 4.4 °C and the average was 5.6 °C (standard deviation 2.8); 10 (12.3%) had at least one negative temperature measured. The average time for participants who had an inadequate temperature record was 8 h and 31 min. Nine participants (90%) who stored the medication into the shelf/drawer below the freezer had a temperature excursion (p = 0.011). Most of the participants (88.5%) who stored their biopharmaceutical near the back side, close to the wall of the refrigerator had a negative temperature record (p < 0.001). Conclusion Most of the study participants (82.71%) did not maintain adequate home storage conditions for their biopharmaceutical. Intrinsic factors of household refrigerators may be involved in temperature deviations.