Ritalin - Methylphenidate - dopamine reuptake inhibitor. Dose usually 30-90mg. Essentuially a long-lasting synthetic cocaine minus the anesthetic effect. It's a stimulant but not as 'strong' as amphetamines and as such it is a lot safer in terms of brain health.
Adderall - amphetamine mixture - essentially 75% destro-amphetamine and 25% laevo-amphetamine. It's the closest thing you're going to get to "street speed" in pharmaceutical form. Dose 10-120mg, depending on tolerance. Adderall XR is an extended release formulation consisting of either a speckled tablet (usually 30mg) or a capsule with beads in it (everything else - read the capsule it's printed with the dosage). These beads (or the tablet) contains a mixture of amphetamine salts that is roughly equivalent to 75% of the "prescribed weight" in amphetamine freebase.
First a primer on salts- amphetamine freebase is an oily corrosive liquid. Hence it is always sold as a salt - usually a sulphate or hydrochloride. These salts dissolve well in water, while the freebase won't dissolve at all and will prefer to stay in hydrocarbon solvents.
The lowdown on dextro versus laevo amphetamines -
Dextroamphetamine is the "centrally active" compound that produces stimulant effects. Releases both norepinephrine and dopamine in good amounts in "normal" dosing.
Laevoamphetamine is basically a super pseudoephedrine - a strong norepinephrine releaser but otherwise not a good central stimulant. Basically this means it makes your body stimulated (increasing heart rate, breathing rate, increasing blood pressure and constricting blood vessels) but doesn't effect your mind so much.
The two compounds are, de facto, created in a 1:1 mixture unless the chemist uses special techniques, called chiral synthesis, to make just one of them. This mixture is called "racemic" amphetamine and is whats seen on the streets of Europe as "speed paste" (mixed with sugar, alcohol, & water).
All amphetamines are absorbed extraordanirally well orally. There is no need to snort or inject them as they can cause damage due to either impurities or their vasoconstrictive effects. Smoking amphetamine salts may cause tooth and gum damage from the volatile chemicals that are created. ("meth mouth")
Adderall was developed as a "special blend" of salts for weight loss, then rebranded as a stimulant for ADD because the manufacturer didn't want to retool their whole production line for a new stimulant. This explains why there is a small 25% balance of laevo-amphetamine salts in it that are not "centrally active".
Vyvanase - lisdexamphetamine - is a chemnical compound of dextroamphetamine adn the amino acid lysine, designed as a sort of chemical time release. Your body has enzymes in the blood that remove thhe lysine molecule and convert it to d-amphetamine. It is essnetnially 60% as potent as an equivalent dose of amphetamine, and should be administered orally.
Dexedrine - dextroamphetamine - is pure D-amphetamine and is the "golden standard" of stimulants.
Desoxyn is D-methamphetamine. It is rarely prescribed for weight loss and ADD/ADHD.
Amphetamine has a half life of 12 hours, whish makes it a rather long-lasting stimulant. Methamphetamine lasts even longer. Methylpheindate, on the other hand, is degraded by the body fairly rapidly (like cocaine) thanks to an ester bridge and so it only has a half life of 1 to 2 hours.
Methylpheidate too is produced in two formulations - a racemic one and the "active" trans-laevo-methylphenidate or "Focalin", which is reputed to be 2x as effective.
The total duration of the compunds in the average individual are as follows -
Methylphenidate, 30mg. - Duration: 3-4h.
Amphetamine, 30mg. - Duration: 6-8h.
Methamphetamine, 30mg. - Duration: 12-18h.
There are of course many offshoots and "research chemicals" that mimic the effects of stimulant NDRI and NDRA's (Norepinephrine Dopamine Reuptake Inhibitors/Release Agents) such as methiopropamine (NDRA, analog of methamphetamine), methcathinone & derivatives (mephedrone, MDPV - NDRI's), ethylphenidate (NDRI), diphenylmethylprolinol (NDRI), 2-DPMP (NDRI), etc.
One should take caution and always research the potency and duration of a compound before experimenting with it.