Subject: why are many medicines 'something-zine HCl'?

In looking at the labelling of several over-the-counter
medicines and adverstisements of prescription medicines in
popular magazines, I see that the active ingredient is
often andquot;something-zine HClandquot;.  I assume andquot;HClandquot; means 
hyrdochloride.  Why do many medicines take this form?  Is
a chlorine atom tacked onto a hydrogen in order to make
the active ingredient water soluble?  Or does this HCl group
have some other function?

Thanks in advance.

Re: why are many medicines 'something-zine HCl'?