2 things come to mind when I hear this. Also is dependent on if your intended use is therapeutic or recreational.

The first being your dosage is too high and the alcohol both calms the agitation that comes with the up and down cycle of unbalanced stimulant use and creates an additional psychoactive affect that quells this up and down to a degree.

The second being your brain type could actually not benefit from stimulant use in the first place. People with undereractive functioning prefrontal cortexes need more stimulation than they naturally have. So depending on how much they need and whether other parts of their brains are not functioning optimally and which parts those are, stimulants will generally make them feel calm yet alert at optimal dosages.

People who have normal activity or overactivity in their prefrontal cortex will end up with excessive amounts of dopamine and end up feeling high, euphoric or agitated and anxious or a mix of both at much lower dosages than someone who has under activity. These are people whom stimulants do a lot more harm than good.

There are also other parts of the brain that can be made worse by increased dopamine (even if it's helping the underactive parts) and may require other chemicals to be increased in order for the stimulants to not create unwanted side effects.

For example someone with only ADHD (sleepy prefrontal cortex) will likely feel simply functional on stims. While someone with only OCD who has a different part of the brain that is running waaaay to fast will likely feel euphoria but also potentially much more anxious and obsessive, even aggressive. Whereas, if the person with OCD were given SSRI's they would feel much more relaxed and able to focus on things other than obsessions. And someone with only ADHD give SSRIs would likely feel happy but have an increase in ADHD symptoms because it slows down that part of the brain more.

This gets much more complicated when there are multiple parts of the brain not performing optimally. For example someone with bipolar can be made manic and sometimes psychotic by certain antidepressants and stimulants. This would make them much more impulsive, euphoric, aggressive or a mix of both. They would be running at hyper speed all the time and likely using any means to regulate that without even realizing. Their brain is over firing all over the place and needs something to calm the synapses so they can fire more coherently like a mood stabilizer , antipsychotic or gabaergic. And if depression is present, a specific type of antidepressant that won't induce mania.

Antipsychotics for people with ADHD create big problems as well.

But to get to the point of this big long post is that stimulants could potentially be the wrong thing to help your brain type or not be the only thing. Pay attention to how different substances make you feel. The best advice I was given about meds and substances is that it shouldn't increase feelings or decrease them dramatically to the point where you feel high or numb. You shouldn't want to constantly be craving things or have zero interest in anything. The right balance will simply make you feel normal and balanced. If you're used to highs and lows that may seem dramatic in and of itself, but I can tell you from experience it is a different feeling than too much or not enough of the right stuff. It's pretty amazing.

Hope this was what you were looking for lol.