Background: In ALS, determining whether individuals have a substantial response to therapy is a challenge for the field. ALS naturally progresses at variable rates and a personalized approach is required to determine if individuals have a substantial response. A new method to evaluate individual response is proposed and applied to data from the CENTAUR trial of sodium phenylbutyrate/ursodoxicoltaurine (PB/TURSO). Methods: In a post hoc analysis, CENTAUR participants whose actual rate of change from baseline in the ALSFRS-R at week 18 was ≤ their own trial baseline progression rate (ΔFS) were defined as having a substantial individual response in slowing ALS progression. Results: Substantial individual response was observed in a greater proportion of participants receiving PB/TURSO (41%, n=87) vs placebo (19%, n=48; P=0.0076). Conclusions: Response versus ΔFS provides a personalized metric to determine substantial individual response in ALS. ΔFS has been shown to be highly correlated with, but to proportionally underestimate, ALSFRS-R decline in clinical trials. Consequently, those who outperform the ΔFS may be considered to have a substantial individual response. Application to CENTAUR data demonstrates a greater proportion of participants with a substantial individual response in the PB/TURSO arm. These methods may enable greater personalization and analysis of individual response in ALS.