Hyoscine hydrobromide, also known as scopolamine hydrobromide, is a medication used in the treatment of motion sickness and postoperative nausea and vomiting. One common side effect is drowsiness. Scopolamine is a tropane alkaloid drug that acts as a competitive antagonist at muscarinic acetylcholine receptors; it is thus classified as an anticholinergic, antimuscarinic drug. Although it is usually referred to as a nonspecific antagonist, there is indirect evidence for m1-receptor subtype specificity.