OPRM1 and gastroesophageal reflux disease: Farmers in our study used leaves and plants of opium poppy (Papaver somniferum) to treat diarrhoea in their poultry. This implies using the side effects of pain treatment with opioids: hard dry stools and increased gastroesophageal reflux. Activation of mu-opioid receptors by opoids in the gastrointestinal tract is responsible for inhibition of gut motility.