{{Chimiebox général|
nom = Éphédrine | 
image = Ephedrine.svg |
tailleimage =  160  |
commentaire = Structure de l'éphédrine |
formule = C<sub>10</sub>H<sub>15</sub>NO |
nom scientifique = (1RS,2SR)-2-(méthylamino)<br/>-1-phénylpropan-1-ol|
CAS = 134-71-4 |
ATC = R03CA02 |
apparence = cristaux blancs ou incolores
}}

L''''éphédrine''' est une amine sympathicomimétique fréquemment utilisée comme décongestionnant. Chimiquement parlant, c'est un alcaloïde dérivé de diverses plantes du genre ''Ephedra'' (famille des Ephedraceae). Son sel, le '''chlorhydrate d'éphédrine''' a diverses utilisations en regard de son effet sympathicomimétique.

==Historique==
L'éphédrine est isolée en 1885 par un pharmacien japonais Nagai Nagayoshi.<ref name="larousse"/>Il la synthétise avec Kanao en 1920.<ref name="synthese"></ref>

L'éphédrine est listée au tableau I de la Convention contre le trafic illicite de stupéfiants et de substances psychotropes de 1988 .

==Chimie==
L'éphédrine présente une isomérie optique et possède deux centres de chiralité. Par convention, les énantiomères qui ont une stéréochimie opposée autour des centres de chiralité sont désignés comme éphédrine, alors que la pseudoéphédrine possède la même stéréochimie autour de ses carbones chiraux. C'est-à-dire, les énantiomères (1''R'',2''R'') et (1''S'',2''S'') sont appelés pseudoéphédrine, alors que les énantiomères (1''R'',2''S'') et (1''S'',2''R'') sont appelés éphédrine. 

L'isomère mis initialement sur le marché est la (-)-(1''R'',2''S'')-éphédrine. (Reynolds, 1988)

Comme la phényléthylamine, l'éphédrine a une structure similaire aux amphétamines. L'éphédrine peut être utilisée dans la synthèse de méthamphétamines par réduction chimique de la fonction alcool.

L'éphédrine est un précurseur très largement utilisé dans la fabrication des méthamphétamines et de la methcathinone. Par oxydation, l'éphédrine peut facilement être synthétisée en methcathinone.

===Synthèse===
Sa synthèse s'obtient en faisant agir du nitroéthane sur du benzaldéhyde et en réduisant le dérivé nitré obtenu en présence de zinc en milieu acétique.<ref name="synthese"/>

==Pharmacologie==
L'éphédrine est une récepteurs adrénergiques.

Elle potentialise l'action de l'adrénaline.

==Usage médical==
thumb|right|Flacons d'éphédrine
L'herbe chinoise traditionnelle ''Ma Huang'' (''Ephedra sinica'') contient de l'éphédrine comme principe actif principal et est utilisé comme antiasthmatique et vasoconstricteur.<ref name="larousse"></ref> Ceci est également vrai pour de nombreuses herbes à base d'extraits d'espèces d'''Ephedra''.

Dans la médecine occidentale, elle a servi de décongestionnant nasal, de bronchodilatateur et contre l'asthme, mais sa popularité décroît face à de nouvelles substances plus sélectives et présentant moins d'effets négatifs. Elle est encore utilisée en intraveineuse contre l'hypotension.

{{drugbox |
| width = 200
| image = Efedryna.svg
| image2 = Ephedrine-3d-CPK.png
| IUPAC_name = (1''R'',2''S'')-2-(methylamino)-1-phenylpropan-1-ol
| CAS_number = 299-42-3
| ATC_prefix=R01
| ATC_suffix=AA03
| ATC_supplemental =  
| PubChem=5032
| DrugBank=DB01364
| C=10 | H=15 | N=1 | O=1
| molecular_weight = 165.23
| bioavailability = 85%
| metabolism = minimal hepatic
| elimination_half-life = 3–6 hours
| excretion = 22-99% renal
| pregnancy_AU = A
| pregnancy_US = A
| pregnancy_category = 
| legal_AU = S4
| legal_CA = Schedule VI 
| legal_UK = P
| legal_US = OTC
| legal_status = 
| routes_of_administration = oral, IV, IM, SC
}}
'''Ephedrine''' (EPH) is a Ephedra'' (family Ephedraceae). It is most usually marketed in the '''hydrochloride''' and '''sulfate''' forms.

In traditional Chinese medicines, the herb ''má huáng'' (麻黄, ''identity of ''soma''.

The production of ephedrine in China has become a multi-million dollar export industry. Companies producing for export extract US$13 million worth of ephedrine from 30,000 tons of ephedra annually, 10 times the amount that is used in traditional Chinese medicine.<ref name=Chen> Long, Professor. http://www.chinadialogue.net/article/show/single/en/692-Chinese-medicine-s-great-waste-of-resources</ref>

==Chemistry==
Ephedrine exhibits optical isomerism and has two chiral centres. By convention the enantiomers with opposite stereochemistry around the chiral centres are designated ephedrine, while pseudoephedrine has same stereochemistry around the chiral carbons. That is, (1''R'',2''R'')- and (1''S'',2''S'')-enantiomers are designated pseudoephedrine; while (1''R'',2''S'')- and (1''S'',2''R'')-enantiomers are designated ephedrine. 

The isomer which is marketed is (-)-(1''R'',2''S'')-ephedrine.<ref name=Reynolds></ref>

As with other phenylethylamines, it is also somewhat chemically similar to methamphetamine, although the amphetamines are more potent and have additional biological effects. 

Ephedrine may also be referred to as: (αR)-α-[(1S)-1-(methylamino)ethyl]benzenemethanol, α-[1-(methylamino)ethyl]benzyl alcohol, or L-erythro-2-(methylamino)-1-phenylpropan-1-ol. Ephedrine hydrochloride has a melting point of 187-188°C.<ref name=Budavari>Budavari S, editor. The Merck Index: An encyclopedia of chemicals, drugs, and biologicals, 12th edition. Whitehouse Station: Merck</ref>

==Mode of action==

Ephedrine is a sympathomimetic amine, principal mechanism of its action relies on its direct and indirect actions on the adrenergic receptor system, which is part of the sympathetic nervous system or ''SNS''.  Central nervous system or ''CNS'' involvement is present, but the predominant clinical effects are caused by involvement with the sympathetic segment of the peripheral nervous system because while ephedrine does cross the blood-brain barrier, it doesn't do this very efficiently (efficient crossers with similar modes of action would include amphetamine and methamphetamine).

Ephedrine increases post-synaptic noradrenergic receptor activity by (weakly) directly activating post-synaptic α-receptors and β-receptors, but the bulk of its effect comes from the pre-synaptic neuron being unable to distinguish between real adrenaline or noradrenaline from ephedrine.  The ephedrine, mixed with noradrenaline, is transported through the noradrenaline reuptake complex and packaged (along with real noradrenaline) into vesicles that reside at the terminal button of a nerve cell.  

As an alkaloid, having some small amount of ephedrine within a noradrenaline vesicle increases the overall pH of the vesicle.  This has the effect of increasing likelihood that the affected vesicle will be released during any subsequent action potential the nerve cell experiences.  The nerve cells in question generally fire at some regular baseline rate; the effect of adding ephedrine is to increase the number of vesicles released during each action potential and possibly to extend the time during which noradrenaline has an opportunity to have an effect on the post-synaptic neuron by virtue of the fact that the reuptake complex has to process both noradrenaline AND ephedrine, presumably a longer process.

Ephedrine's mechanism of action on neurotransmission in the brain is wide. Its action as an agonist at most major noradrenaline receptors and its ability to increase the release of both dopamine and to a lesser extent, serotonin by the same mechanism as explained above for norepinephrine, is presumed to have a major role in its mechanism of action. 

Because of ephedrine's ability to potentiate dopamine neurotransmission it is thought to have addictive properties by some researchers.  The ability to potentiate serotonin and noradrenergic activity is clinically relevant, but is not thought to contribute to the potential for abuse.

While ephedrine's role in the serotonin system is less understood there is preliminary documentation of clinically significant agonism at excitory serotonin receptors, perhaps as a downstream response to the large release of norepinephrine in the nucleus accumbens (commonly referred to as the "pleasure center" of the brain). In mice, stereotypical behaviour was both easily induced by administration of ephedrine and its primary alkaloids and reversed when serotonin antagonists were administered.

==Clinical use==
thumb|right|Ephedrine Sulphate (1932) Ephedrine Compound (1932) and Swan-Myers Ephedrine Inhalant No. 66 (ca. 1940)
===Indications===
Ephedrine was once widely used as a ganglionic blocking agents, antiadrenergic agents, or other medications that lower blood pressure.<ref name=Bicopoulous>Bicopoulos D, editor. AusDI: Drug information for the healthcare professional, 2nd edition. Castle Hill: Pharmaceutical Care Information Services; 2002.</ref> It can be used in narcolepsy and nocturnal enuresis.  It also remains the only non-steriodal drug available to treat the symptoms of certain types of Congenital Myasthenia.

In traditional Chinese medicine, ephedrine has been used in the treatment of asthma and bronchitis for centuries.<ref name=Ford>Ford MD, Delaney KA, Ling LJ, Erickson T, editors. Clinical Toxicology. Philadelphia: WB Saunders; 2001. ISBN 0-7216-5485-1
Research Laboratories; 1996. ISBN 0-911910-12-3</ref> 

An body builders before workouts due to the increased amount of energy and alertness.

For many years, the US Coast Guard recommended ephedrine together with an equal 25 mg dose of promethazine to its sailors to combat seasickness. Promethazine manages nausea and ephedrine fights the ensuing drowsiness. Commonly referred to as the Coast Guard cocktail, ephedrine may still be available for prescription for this purpose.

===Adverse effects===
Adverse drug reactions (ADRs) are more common with systemic administration (e.g. injection or oral administration) compared to topical administration (e.g. nasal instillations). ADRs associated with ephedrine therapy include:<ref name=JFC />

*Cardiovascular: tachycardia, cardiac arrhythmias, Angina pectoris, vasoconstriction with hypertension
*Dermatological: flushing, sweating, acne vulgaris 
*Gastrointestinal: nausea, appetite loss
*Genitourinary: increased urine output due to increased blood flow (difficulty urinating is not uncommon, as alpha-agonists such as ephedrine constrict the internal urethral sphincter, mimicking the effects of sympathetic nervous system stimulation)
*Nervous system:restlessness, confusion, insomnia, mild euphoria, mania/hallucinations (rare except in previously existing psychiatric conditions), delusions, formication (may be possible, but lacks documented evidence) paranoia, hostility, panic, agitation
*Respiratory: dyspnea, pulmonary edema
*Miscellaneous: dizziness, headache, tremor, hyperglycemic reactions

The approved maximum daily dosage of ephedrine for use as a bronchodilator is 150mg, as specified on the packaging of the bronchodilator and expectorant combination, '''Bronkaid''', made by Bayer pharmaceuticals.

Overdose can lead to death, although the approved dose is not likely to cause severe reactions when used as directed.

Ephedrine can also lead to damage of the brain receptors' over a period of high usage; this is because of its constant action on the neurochemicals. It also leads to high increase in blood pressure which over time can lead to damage in the blood vessels.