A critical review is conducted by the Expert Committee in any of the following cases: (1) there has been notification from a Party to the 1961 or the 1971 Convention concerning the scheduling of a substance; (2) there has been an explicit request from the UN Commission on Narcotic Drugs to review a substance; (3) pre-review of a substance has resulted in a recommendation for critical review; (4) information is brought to the attention of WHO that a substance of especially serious risk to public health and society, and of no recognized therapeutic use by any Member State is clandestinely manufactured. If therapeutic use of the substance is confirmed subsequently by any Member State in respect of case (4), the substance shall be subject to a pre-review.

All the five substances under critical review at the present meeting were pre-reviewed at the previous meeting of the Committee (4) and recommended for critical review.