Chandy suggested
Consistent with the toxicity of isoniazid in slow acetylators, there is an increased incidence of other drug toxicities in subjects carrying defective alleles, such as lupus erythematosus in patients treated with hydralazine or procainamide (Sim et al., 1988), and haemolytic anemia and inflammatory bowel disease after treatment with sulfasalazine (Chen et al., 2007)
The third counter is the opportunity-cost argument
Springer, Cham Lin JT, Liu CW, Chen YC, Hu CC, Juang LD, Shiesh CC, Yang DJ (2014) Chemical composition, antioxidant and anti-inflammatory properties for ethanolic extracts from Pleurotus eryngii fruiting bodies harvested at different time
However, these pharmacies are more limited in scale and can make GLP-1s for only a narrow set of reasons, not routine prescriptions