Hyoscyamine

Hyoscyamine is a naturally occurring tropane alkaloid that blocks muscarinic acetylcholine receptors. It reduces smooth-muscle spasms and secretions, but can also cause anticholinergic effects.

Muscarinic acetylcholine receptor: A G-protein-coupled receptor activated by acetylcholine and blocked by antimuscarinic drugs. Hyoscyamine reduces parasympathetic signaling by blocking these receptors.
Antispasmodic: A medication that reduces involuntary muscle spasms, especially in smooth muscle. Hyoscyamine is used chiefly for its antispasmodic action.
Tropane alkaloid: An alkaloid containing a tropane ring system, a structural feature found in several plant-derived drugs. Hyoscyamine belongs to this chemical family.
Atropine: A tropane alkaloid medication that blocks muscarinic acetylcholine receptors. Atropine is the racemic form associated with hyoscyamine, while hyoscyamine is its naturally active levorotatory form.
Acetylcholine: A neurotransmitter used by neurons at neuromuscular junctions and throughout the parasympathetic nervous system. Hyoscyamine opposes acetylcholine at muscarinic receptors.
Irritable bowel syndrome: A chronic disorder characterized by abdominal pain and altered bowel habits without detectable structural disease. Hyoscyamine may be prescribed to relieve cramping in some cases.
Solanaceae: A flowering-plant family that includes potatoes, tomatoes, tobacco, and several alkaloid-producing species. Hyoscyamine occurs in certain members of this family.
Ipratropium: A quaternary ammonium antimuscarinic drug used mainly as an inhaled bronchodilator. Unlike hyoscyamine, ipratropium is designed for local inhaled effects with limited systemic absorption.
Parasympathetic nervous system: The autonomic nervous system division that supports functions such as digestion, urination, and slowing the heart. Blocking its muscarinic signaling accounts for many of hyoscyamine’s bodily effects.
Gastrointestinal spasm: An involuntary contraction of smooth muscle in the digestive tract that can cause cramping pain. Reducing these contractions is a direct therapeutic aim of hyoscyamine.

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