Ticagrelor is associated with more prompt and potent antiplatelet effects compared with clopidogrel, leading to better clinical outcomes, including reduced cardiovascular mortality, across the spectrum of patients with acute coronary syndrome, including those with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PCI). However, in this latter setting a delay in the onset of its antiplatelet effects has been shown. Morphine has been identified as a cause of delayed P2Y12 inhibition in patients with STEMI. In fact, opiates are known to inhibit gastric emptying, leading to delayed absorption and potentially decreasing peak plasma levels of orally administered drugs. Methylnaltrexone is a parenteral peripheral opioid receptor antagonist which has the potential to prevent or reverse opioid-induced peripherally mediated side effects (i.e. gastric emptying inhibition) without affecting analgesia. Studies have shown that methylnaltrexone effectively prevented morphine-induced gut motility change. However, whether the use of intravenous methylnaltrexone may overcome the effects of morphine administration on the pharmacokinetic (PK) and pharmacodynamics (PD) profiles of ticagrelor has not been investigated yet. The proposed investigation will include patients with coronary artery disease and will have a prospective, randomized, cross-over design. Patients will be randomized to receive either intravenous methylnaltrexone or placebo. Immediately after methylnaltrexone administration, patients will receive intravenous morphine and then will receive a 180-mg ticagrelor loading dose 15 minutes after morphine administration. After a 7 ± 2 days wash-out period, patients will cross-over to the alternate study-treatment arm. At each visit, blood samples for PK and PD assessments will be collected at several time points. This study will provide insights on a possible treatment strategy to overcome the impaired P2Y12 inhibition induced by morphine.