Amphetamine is a chiral molecule that has isomers. Specifically it has a single stereocenter, which means it has two possible stereoisomers [D-amphetamine, L-amphetamine] that are non-superimposable mirror images of each other. Furthermore these two stereoisomers are also enantiomers, which are designated as (R)-amphetamine and (S)-amphetamine. From a pharmacological point of view the the different enantiomers each attribute to different psychoactive effects where D-amphetamine [(R)-amphetamine] has a higher activity on dopamine receptors responsible for alertness, reaction speed, concentration, memory and much more. In higher doses the stimulation of these specific receptors causes euphoria whereas L-amphetamine contributes to the negative effects of the drug and is the main culprit often responsible for the comedown sickness and the nausea.
Using stereochemistry one can isolate dextro from levo isolating pure D-amphetamine. In theory this should be the most pleasant euphoric experience with the least side-effects possible. The easiest way is to react racemic amphetamine with L-tartaric acid. In this reaction the acid only reacts with levo orientation making it possible to extract the unreacted dextro orientation.
Methamphetamine on the other hand is a different compound altogether (different chemical formula). By nature it is more potent than amphetamine because of the added methyl group (CH3-). This makes it more lipophilic. The primary result of this is the ability to readily pass the blood-brain-barrier immediately once it is carried by blood cells to which it adheres from the lungs (if smoked). This property also leads to prolonged effects and increased potency as it also accumulates in the fatty tissues across the body making it harder for the body to metabolize. In the brain it is metabolized by MAOs which are a family of enzymes that are responsible for the breakdown of monoamine neurotransmitters such as [dopamine, norepinephrine, serotonin]. MAOs convert methamphetamine to amphetamine directly in the brain causing immediate and highly potent effects compared to administering amphetamine. Additionally, it can also be metabolized by other enzymes such as cytochrome P450 (CYP450) enzymes, but this is a minor pathway compared to MAO-mediated metabolism.
In terms of psychological effects they are basically the exact same thing with methamphetamine simply being much more potent.
Using stereochemistry one can isolate dextro from levo isolating pure D-amphetamine. In theory this should be the most pleasant euphoric experience with the least side-effects possible. The easiest way is to react racemic amphetamine with L-tartaric acid. In this reaction the acid only reacts with levo orientation making it possible to extract the unreacted dextro orientation.
Methamphetamine on the other hand is a different compound altogether (different chemical formula). By nature it is more potent than amphetamine because of the added methyl group (CH3-). This makes it more lipophilic. The primary result of this is the ability to readily pass the blood-brain-barrier immediately once it is carried by blood cells to which it adheres from the lungs (if smoked). This property also leads to prolonged effects and increased potency as it also accumulates in the fatty tissues across the body making it harder for the body to metabolize. In the brain it is metabolized by MAOs which are a family of enzymes that are responsible for the breakdown of monoamine neurotransmitters such as [dopamine, norepinephrine, serotonin]. MAOs convert methamphetamine to amphetamine directly in the brain causing immediate and highly potent effects compared to administering amphetamine. Additionally, it can also be metabolized by other enzymes such as cytochrome P450 (CYP450) enzymes, but this is a minor pathway compared to MAO-mediated metabolism.
In terms of psychological effects they are basically the exact same thing with methamphetamine simply being much more potent.