Surely your Ethics Committee (or IRB) will help with advice and will approve any arrangement for benefits for subjects and hence they will be approved and therefore acceptable. All payments and inducements must be approved by your Ethics Committee. In Phase one clinics it is sometimes acceptable to pay subjects for the large amount of time they spend in the clinic performing tests. It is never acceptable to pay them for any additional risk they are taking or to make such a large payment so as to be an inducement. In other phases of clinical development, subjects are generally not sequestered in a research clinic for long periods of time and the subjects are generally expected to gain some benefit from participation. Hence other phase trials generally do not make payment for subject's time.