There's a lot of individual variability on this point. Many people might have a higher susceptibility to similar substances (like heroin and oxycodone), then to a slightly lesser degree broader groups like "uppers" or "downers," and then finally some people will take anything they can get their hands on.

There are wrinkles to that general formula. Some people only want cocaine and have no affinity for amphetamines, but will take opiates or benzodiazepines without discrimination.

It's pretty messy, sorry I don't have a better answer but's that's how it is.