Flibanserin is a non-hormonal oral medication classified as a Multifunctional Serotonin Agonist and Antagonist (MSAA). It is primarily indicated for treating Hypoactive Sexual Desire Disorder (HSDD) in premenopausal women. 

Medical Description and Indications

• Target Population: It is used in premenopausal women under 65 years old to treat acquired, generalized HSDD characterized by low sexual desire that causes significant distress or interpersonal difficulty.
• Exclusions: It is not intended for use in men, postmenopausal women, or for enhancing general sexual performance. It should not be used if the condition is caused by a co-existing medical or psychiatric issue (e.g., depression), relationship problems, or side effects from other medications.
• Clinical Efficacy: In trials reviewed by the NEJM and AAFP, flibanserin demonstrated a modest increase in satisfying sexual events (SSEs) and sexual desire scores compared to a placebo. 

Pharmacological Mechanism
Flibanserin acts on the central nervous system to rebalance neurotransmitters involved in the sexual response cycle. 

• Serotonin Modulation: It acts as a postsynaptic 5-HT1A receptor agonist and a 5-HT2A receptor antagonist.
• Neurotransmitter Release: This activity results in an increase of dopamine and norepinephrine (excitatory neurotransmitters) and a decrease in serotonin (an inhibitory neurotransmitter) specifically in the prefrontal cortex. 

Clinical Pharmacology and Metabolism

• Dosage: The recommended dose is 100 mg taken orally once daily at bedtime. Bedtime administration is critical to reduce the risk of daytime sedation, hypotension, and syncope.
• Absorption: It has an absolute bioavailability of approximately 33%. Taking it with food increases absorption by up to 56%.
• Metabolism: It is extensively metabolized in the liver, primarily by the CYP3A4 enzyme and, to a lesser extent, by CYP2C19.
• Elimination: The average terminal half-life is about 11 hours. 

Safety and Contraindications 

• Alcohol Interaction: It carries a Boxed Warning due to the risk of severe hypotension and syncope when combined with alcohol. Current labels advise not consuming alcohol within two hours of taking flibanserin.
• Drug Interactions: It is contraindicated with moderate or strong CYP3A4 inhibitors (e.g., fluconazole, ketoconazole, grapefruit juice) which can dangerously increase drug levels.
• Liver Health: Contraindicated in patients with hepatic impairment (liver disease) due to significantly increased exposure.
• Common Side Effects: Dizziness, somnolence (sleepiness), nausea, fatigue, insomnia, and dry mouth.