They act in different ways to increase dopamine in the brain. Cocaine works by blocking the dopamine transporter; that is, it doesn’t allow dopamine to be recycled back into the neuron after it has done its work. Methamphetamine interferes with this recycling process as well, but it also causes too much dopamine to be released. Another difference is that cocaine disappears from the brain quickly, while methamphetamine stays much longer. The long presence in the brain ultimately makes methamphetamine very harmful to brain cells.