Provocholine was first approved by the FDA in 1986 and since then has been included in various asthma, and bronchial challenge testing guidelines (both international and UK specific). Here are links to some examples of relevant guidelines/recommendations which include the methacholine challenge test;

NICE Guideline (NG80) Asthma: diagnosis, monitoring and chronic asthma management (2020)

British Guideline on the management of asthma (2019)

ERS technical standard on bronchial challenge testing: general considerations and performance of methacholine challenge tests

Coates AL, Wanger J, Cockcroft DW, et al.
EurRespir J 2017; 49: 1601526 [].

Guidelines for Methacholine and Exercise Challenge Testing—1999

Crapo RO, Casaburi R, Coates AL, et al.
Am J RespirCrit Care Med 2000; 161: 309–329