Approximately 5% of the population experiences a phenomenon termed "musical anhedonia", in which individuals do not experience pleasure from listening to emotionally arousing music despite having the ability to perceive the intended emotion that is conveyed in passages of music. A clinical study from January 2019 that assessed the effect of a dopamine precursor (levodopa), dopamine antagonist (risperidone), and a placebo on reward responses to music – including the degree of pleasure experienced during musical chills, as measured by changes in electrodermal activity as well as subjective ratings – found that the manipulation of dopamine neurotransmission bidirectionally regulates pleasure cognition (specifically, the hedonic impact of music) in human subjects. This research suggests that increased dopamine neurotransmission acts as a "sine qua non" condition for pleasurable hedonic reactions to music in humans. The various stages of copulation may also be described as inducing euphoria in some people. Various analysts have described either the entire act of copulation, the moments leading to orgasm, or the orgasm itself as the pinnacle of human pleasure or euphoria. A euphoriant is a type of psychoactive drug which tends to induce euphoria. Most euphoriants are addictive drugs due to their reinforcing properties and ability to activate the brain's reward system. Dopaminergic stimulants like amphetamine, methamphetamine, cocaine, MDMA, and methylphenidate are euphoriants. Nicotine is a parasympathetic stimulant that acts as a mild euphoriant in some people. Chewing areca nut (seeds from the "Areca catechu" palm) with slaked lime (calcium hydroxide) – a common practice in South- and Southeast Asia – produces stimulant effects and euphoria. The major psychoactive ingredients – arecoline (a muscarinic receptor partial agonist) and arecaidine (a GABA reuptake inhibitor) – are responsible for the euphoric effect. Certain depressants can produce euphoria; some of the euphoriant drugs in this class include alcohol in moderate doses, , and ketamine. Some barbiturates and benzodiazepines may cause euphoria. Euphoriant effects are determined by the drug's speed of onset, increasing dose, and with intravenous administration. Barbiturates more likely to cause euphoria include amobarbital, secobarbital and pentobarbital. Benzodiazepines more likely to cause euphoria are flunitrazepam, alprazolam and clonazepam.