Yep, it completely antagonizes the dopaminergic effects and leaves you feeling like a zombie. A complete buzz-kill, literally.
That is why taking benzodiazepines with stimulants is a waste, unless the idea actually is to counteract the stimulant. There are sedatives and hypnotics which do not do this, but they are not as common as they once were -- like barbiturates and non-barbiturate sedative-hypnotics.. There was more than one manufacturer who made a combination of dextroamphetamine and secobarbitone in a capsule, and a version with three colours of beads in it which also had hyoscine (scopolamine) in it, which was really good to mix with Percs, Vikes, Tylenol With Codeine Nº 4, Emprazil With Codeine Nº 5, and Synalgos DC for pain
Booze and pot are also popular to take with speed, of course. I think that narcotics are better to combine with speed and vice versa, but I think narcotics are better to combine with everything . . .
Taking the downers with C-Jam is popular too, like eight lines of Bolivian Marching Powder and several reds (secobarbitone) which can have an effect of anything from pleasant, aware calm to essentially turning into a werewolf . . . Methylphenidate with methaqualone is a great combination . . .
The only combination I have heard of with benzodiazepines and stimulants are the people who like to take acid with Valium, but not being an acid fancier, I am not sure what the attraction is . . .
Doing amphetamines with barbiturates or meprobamate and other downers is known as a set-up, and these combinations were actually available as diet pills from the 1930s to the early 1980s. Combinations of amphetamine, dextroamphetamine, methamphetamine and a couple of others with meprobamate were big both as diet pills (Appetrol) and less-sleepy versions of meprobamate for daytime sedation, and I think there may have been a diet pill with amphetamine, meth, and meprobamate with sodium bicarbonate in it too; Dexamyl was a very popular diet pill which was dextroamphetamine and amobarbitone, known as Christmas Trees and I think the Eskatrol Jimmy Buffett sings about was dextroamphetamine plus prochlorperazine . . . the bottle of rum with it would make it feel better as the prochlorperazine is a downer but surely not a barbiturate . . .