that's a street name for chlorpromazine in the Republic of Zimbabwe. It's used to treat people with schizophrenia, bipolar disorder, and acute psychosis but is widely abused by some Zimbos for recreational purposes, especially in poor high-density areas.
Oftentimes, people confuse dombo with mutoriro, assuming it means the same thing for the latter, when in fact that's not the case at all. Mutoriro is simply crystal methamphetamine aka ice or glass.
Lastly, if you find yourself in a habit of taking dombo you are supposed to religiously and steadfastly stay off the liquor just as much as you do when you are sipping ngoma ("codeine cough syrup") otherwise, trouble.