These are both very large topics, about which there is ongoing disagreement in the scientific literature (unless the scientific literature has changed a lot since my last major data corpus update).

A reasonably well regarded abstract from a 2005 lit review on Alzheimers by Paul T Francis starts: "Evidence exists for both cholinergic and glutamatergic involvement in the etiology of Alzheimer's disease. Acetylcholine (ACh), a neurotransmitter essential for processing memory and learning, is decreased in both concentration and function in patients with Alzheimer's disease. This deficit and other presynaptic cholinergic deficits, including loss of cholinergic neurons and decreased acetylcholinesterase activity, underscore the cholinergic hypothesis of Alzheimer's disease. The glutamatergic hypothesis links cognitive decline in patients with Alzheimer's to neuronal damage resulting from overactivation of N-methyl-d-aspartate (NMDA) receptors by glutamate. The sustained low-level activation of NMDA receptors, which are pivotal in learning and memory, may result from deficiencies in glutamate reuptake by astroglial cells in the synaptic cleft."

Methylphenidate is the generic name of a drug with trademarks that include Ritalin and Concerta, which is quite similar to meth, but different enough that the US FDA has chosen to tolerate it as a prescription drug in spite of the risk of addiction and abuse. A 2018 lit review by Stephen V Faraone on the similarities and differences included: "The primary pharmacologic effect of both amphetamine and methylphenidate is to increase central dopamine and norepinephrine activity, which impacts executive and attentional function. Amphetamine actions include dopamine and norepinephrine transporter inhibition, vesicular monoamine transporter 2 (VMAT-2) inhibition, and monoamine oxidase activity inhibition. Methylphenidate actions include dopamine and norepinephrine transporter inhibition, agonist activity at the serotonin type 1A receptor, and redistribution of the VMAT-2. There is also evidence for interactions with glutamate and opioid systems."

One of the very few overlaps here (other than broad claims like "they are both related to the brain") is a possible involvement of the glutamate system in both Alzheimers and Ritalin, which both quotes contain, but neither quote dwell on as being of central interest.
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