A bit more complicated than that. Meth isn't just a dopamine releasing agent, it's also a DRI in and of itself (at lower doses this effect is more pronounced), as well as an MAO-B substrate (basically takes up the enzyme responsible for metabolizing not just methamphetamine, but things like dopamine, phenethylamine (a TAAR1 agonist), norepinephrine. Meth is also, in and of itself, a TAAR1 agonist (trace amine autoreceptor). In high doses, it's releasing properties are so powerful and vast, it ends up forcing dopamine (as well as norepinephrine and to a large extent serotonin as well) to released in reverse back outward from the dopamine/serotonin transporters. Think a massive traffic highway collision, with backups/pileups. See, there is even things like N-methylphenethylamine, that your brain produce in small amounts during peak experiences, self regulating process and whatnot, and its only one carbon away from methamphetamine so the metabolism blockade is very real, just by virtue of introducing such a similar molecule into the same limited, confined space (your body/brain). It does force the brain to produce more dopamine, however that just gets fed into the same process, all discombobulated and whatnot, and even with all the dopamine in the world the receptors eventually get downgraded to the point where youre only feeling the positive effects upon the initial burst/rush of dopamine induced by peak levels of the drug.