Study of TAK-935 as an Adjunctive Therapy in Adult Participants With Complex Regional Pain Syndrome (CRPS)

Inclusion Criteria: 1. Participant meets the Budapest clinical diagnosis of complex regional pain syndrome (CRPS) at the screening visit and is at least 6 months since onset of symptoms. 2. Participant's pain medications and nondrug treatments must be stable (regimented per prescription) for 1 month prior to screening and remain stable throughout Part A. 3. Participant agrees to use a single previously prescribed rescue medication within the prescribed dose during Part A of the study and to record the daily use of these medications. 4. Participant must have an average 24-hour pain intensity score ≥4 and ≤9 on the 24-hour average pain intensity numeric pain scale (NPS) during screening/baseline. This score will be calculated by averaging the daily 24 hour pain intensity scores for the past seven days prior to randomization. The participant must have daily 24-hour pain intensity scores recorded for at least 6 of the past 7 days. Exclusion Criteria: 1. Currently receiving intravenous (IV) or oral ketamine, history of IV or oral ketamine use within the past 6 weeks prior to screening, or planned use of IV or oral ketamine during this study. 2. Participant is receiving chronic opioid treatment at a dose that has not been stable 28 days prior to screening. 3. Participant is receiving chronic opioid treatment \>160 mg of morphine equivalent per day. 4. Participant has a positive drug screen for phencyclidine, amphetamine/ methamphetamine, or cocaine at screening. Cannabis is allowed.. 5. Participant is positive for hepatitis B or hepatitis C infection at screening. (Note that participants who have been vaccinated against hepatitis B \[hepatitis B surface antibody {Ab}-positive\] who are negative for other markers of prior hepatitis B infection \[eg, negative for hepatitis B core Ab\] are eligible. Also, note that participants who are positive for hepatitis C Ab are eligible if they have a negative hepatitis C viral load by quantitative polymerase chain reaction).