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Methylphenidate hydrochloride is a psychostimulant drug commonly used to treat patients with conditions such as ADD/ADHD and Narcolepsy.
It has shown some success as a treatment for those affected by treatment-resistant depression, eating disorders and as a replacement therapy for patients affected by cocaine or methamphetamine addiction.
It functions by blocking re-uptake of dopamine, noradrenaline and (to a lesser extent) serotonin in the brain. It's effects are increased alertness and concentration, side effects include anxiety, tachycardia, and chest pain in higher doses.
Methylphenidate is a synthetic central nervous system stimulant--also well described as a substituted amphetamine, though its mechanism of action is distinct from the classical amphetamines-- which is prescribed worldwide for a variety of diagnoses, such as Attention-Deficit (Hyperactivity) Disorder, Postural Orthostatic Tachycardia Syndrome, Chronic Fatigue Syndrome, narcolepsy, depression, obesity and (rarely) Obsessive-Compulsive Disorder. It has been shown to possess neuroprotective effects.  It is sold as a racemic mixture under the brand names Ritalin, Ritilana, Ritaline, Attenta, Penid, Ribufen, Concerta, Metadate, Methylin and Daytrana.
The compound itself is a member of the piperidine class, and despite not being a member of the same family, it bears some structural resemblance to amphetamine but its effects are likened to those of cocaine.
It is most commonly sold as the water-soluble salt, methylphenidate hydrochloride.
Methylphendate can provide a very satisfying high, However, when repeatedly abused, the user can build a tolerance to this drug very quickly, a high tolerance will reduce both the recreational and medicinal value of the drug.
Ritalin 10mg (Novartis)
Intranasal or Intravenous use.
 The slow-release mechanism of transdermal patches intentionally decreases the recreational potential of a drug, but is ideal for treatment.
The oral bioavailability of methylphenidate ranges between 11-52%
Snorting crushed tablets may cause damage to the inside of the nose via vasoconstriction by the drug itself and corrosion by binders used in pill manufacture. As with cocaine, it is reasonable to assume that long-term abuse in this manner may lead to permanent damage, including destruction of the septum, which separates the nostrils. Thus, it is advised that an extraction be performed to obtain a relatively pure methylphenidate hydrochloride before attempting this, though extraction may reduce, but does not eliminate the potential for damage.
comedown effects similar to those of amphetamines and cocaine, though usually less severe, The comedown effects commonly include
Chronic abuse or very high doses can lead to auditory hallucinations and stimulant psychosis.  The long-term effects of methylphenidate use are unknown. 
Amphetamine is a drug with similar effects as methylphenidate; it has the same indications, especially ADD/ADHD. However, methylphenidate is not an amphetamine, despite structural resemblances. Amphetamine's action slightly differs from methylphenidate's insofar as it also promotes the release of neurotransmitters into the synapse and significantly affects serotonin. 
A Drugs-Forum poll shows a significant majority of users preferring the effects of Adderall (mixed amphetamine salts) over methylphenidate.
alcohol (ethanol) can enhance euphoria, libido and sociability as well as counteracting alcohol's drowsiness. It also often makes the user feel less drunk than they really are, and can be dangerous for this reason.
Ethylphenidate is a homologue of methylphenidate, which has an ethyl - instead of a methyl - group attached to the single-bonded oxygen of the acetate. This is shown in the above diagram by an extra angle at the top-left, representing the replacement of the methyl's last hydrogen with one carbon and three hydrogens.
Ethylphenidate is created in the human body when ethanol and methylphenidate are ingested at the same time, by a process called transesterification. The liver removes the methyl from methylphenidate and the ethyl from ethanol. Methanol is an expected byproduct of this reaction, but in such insignificant quantities as to pose no real risk to the body, especially due to the presence of ethanol, which is an antidote to poisoning by the former. The same process results in the formation of cocaethylene when cocaine and alcohol are co-ingested. 
Selective serotonin reuptake inhibitors are prescribed for the treatment of depression, anxiety and Obsessive-Compulsive Disorder. There are no serious dangers inherent to combining methylphenidate with an SSRI. Some antidepressants, such as venlafaxine (Effexor), also inhibit the reuptake of noradrenaline, which can cause feelings of agitation and panic attacks when combined with methylphenidate.
Monoamine oxidase inhibitors are last resort antidepressants which inhibit the action of an enzyme called monoamine oxidase (MAO). MAO's function involves deanimation through the oxidation of monoamine compounds (such as neurotransmitters serotonin, dopamine and noradrenaline), which renders them inactive. By inhibiting this enzyme, the levels of these monoamines increase.
Methylphenidate should never be taken with an MAOI, and up to two to six weeks or more after taking any MAOI, since the rise in dopamine, norepinephrine, and serotonin levels associated with methylphenidate usage could provoke hypertensive crisis, serotonin syndrome, stroke, heart attack and death. The clinical use of combinations of stimulants, such as methylphenidate, and MAOIs is exclusively done in a hospital setting under very close medical supervision.
Methylphenidate is a dopamine and noradrenaline/norepinephrine reuptake inhibitor (DNRI). It competitively binds to the transporter proteins which remove these neurotransmitters from the synaptic cleft, thereby allowing them to agonise receptors for longer. This is similar to the mechanism by which SSRI antidepressants inhibit the reuptake of serotonin. 
Dopamine and Noradrenaline
Endogenous phenethylamine neurotransmitters.
It's primary metabolic path is hepatic by the cytochrome P450 as a substrate inhibitor of enzyme CYP2D6.
Investigated as a carcinogen, mutagen and teratogen. No evidence of such activity found. (expand + source)
Methylphenidate was first synthesised 1944 in Basel, Switzerland, by Ciba (Chemische Industrie Basel). 
Popularity of Methylphenidate over time:
Drugs Act 1984, section 8, subsection 1b)
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