BP be careful in parts of Amsterdam too!
Well, the advice is the same. Never share whatever implement/protection you use to achieve whatever mental/physical state you desire, with anybody else.
If you employ the services of certain ladies, they will provide the necessary protection as part of the deal. And if you visit smart shops, coffee shops and such, all the necessary stuff to enjoy things safely can be bought there too.
As far as illegal stuff (yes there is some that's illegal, even in Amsterdam): The Dutch government even has programs in place where registered drugs addicts can exchange their needles for free. So much for Darwin...
(I'm not going to be more specific or explicit, otherwise the mods might throw me out. But for me, I just make sure my beerglass is clean.)