With regard to ketamine, at present there are no absolute contraindications with concomitant medications. However, there are potential risks related to medications that could amplify the sedative effects of ketamine, such as opioids, benzodiazepines, gabapentin or alcohol. Also, there are some reports that GABA active medications (e.g., benzodiazepines) can reduce treatment response, though this has not been consistently found to be the case.
With regard to TMS, there is research suggesting that concomitant benzodiazepine use can worsen outcomes.