If alcohol and marijuana are both believed to increase the dopamine in your brain, why do they produce different highs?
There are many differences between alcohol and marijuana highs. [1]  Alcohol has a higher potential to cause health issues, and can even lead to death if consumed in excess.  [1][2]  Marijuana, on the other hand, has almost no health risks, and would have to be consumed in high amounts to even approach the toxicity of alcohol. [1]  Marijuana also has many other benefits, like aiding with pain and inflammation. [3]
Although alcohol and marijuana seem to have commonalities in that both increase dopamine in users' brains, there are important differences in how they work [1, 2]. For example, while alcohol affects the cerebellum and the cerebral cortex, lowering inhibitions, marijuana works by targeting receptors in the brain, the central nervous system, and throughout the body [1, 2]. Additionally, the effects of alcohol on the cerebellum and cerebral cortex can cause a person to lose balance and coordination, whereas marijuana affects the receptors and the nervous system, with effects that can include restoring, and even enhancing, neurogenesis in the hippocampus [1, 2]. Cannabis also appears to have positive effects on the brain later in life, counteracting age-related memory impairments and depression [2]. This means that whereas alcohol is likely to erode your brain, marijuana may help your brain function better in certain ways [2].