A clinical hold is an order by FDA that immediately suspends or imposes restrictions on an ongoing or proposed clinical study. FDA has promulgated regulations authorizing clinical holds for studies involving drugs and biological products. Section 312.42(a) provides the scope and effect of a clinical hold order:

A clinical hold is an order issued by FDA to the sponsor to delay a proposed clinical investigation or to suspend an ongoing investigation. The clinical hold order may apply to one or more of the investigations covered by an IND. When a proposed study is placed on clinical hold, subjects may not be given the investigational drug. When an ongoing study is placed on clinical hold, no new subjects may be recruited to the study and placed on the investigational drug; patients already in the study should be taken off therapy involving the investigational drug unless specifically permitted by FDA in the interest of patient safety. A clinical hold may be complete or partial. Delay or suspension of all clinical work under an IND is considered a complete clinical hold. Delay or suspension of only part of the clinical work under an IND is considered a partial clinical hold. A partial clinical hold could, for example, be imposed to delay or suspend one of several protocols in an IND, a part of a protocol, or a specific study site in a multi-site investigation. FDA's regulation authorizing clinical holds on studies of drugs and biological products sets forth grounds for imposing a hold. Those grounds vary depending on the nature of the study. For all types of studies, however, FDA may impose a clinical hold if it finds that “human subjects are or would be exposed to an unreasonable and significant risk of illness or injury."

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