In a placebo controlled trial the treatment arms are as follows:

Treatment Arm A IMP + Therapy A + Therapy B
Treatment Arm B Placebo + Therapy A + Therapy B

Therapy A & B are both marketed products used per their authorised forms, and are typically used in combination with other drugs as part of a regimen. Should therapy A & B be classified as IMP?

One line of thought is that they meet the criteria of background treatment and are therefore NIMPs. Another opinion is that they are part of investigational treatment regimens and are therefore IMPs. What is the impact of classifying incorrectly?

Thanks in advance for your thoughts