Opioids act on opioid receptors located in the brain as well as in the gastrointestinal (GI) tract to induce changes in motility. A variety of studies have linked chronic opioid use with changes in intestinal and to a lesser extent esophageal motility. Less is known about acute administration effects on distal esophageal motility and LES and even less with respect to proximal esophagus, UES and pharynx. Codeine, an opioid receptor agonist, by acting both centrally as well as in the periphery may induce changes in parts of the GI tract implicated in deglutition. Therefore, to evaluate the hypothesis the researchers will study motility patterns in the pharynx, UES, proximal and distal esophagus and LES in 22 healthy volunteers receiving placebo or codeine (60 mg) in a double-blind randomized cross-over controlled fashion. Motility patterns will be studied using state-of-the-art criteria and analytic tools (Chicago 3.0, AIMPlot analysis).

Inclusion Criteria:

• Healthy volunteers aged between 18-60 years old
• Written informed consent

Exclusion Criteria:

• No chronic disease/medication
• No GI symptoms
• Not pregnant or breast-feeding
• No history of head/neck surgery
• Not allergic to codeine

Double-blind, preparation and administration of codeine or placebo conducted by an independent researcher.