where clauses with and

Here's an odd one:
I can't seem to make a where clause containing 'and' work

db=# select orgname,usertype from users where usertype='Drug
Addiction';
              orgname               |    usertype
------------------------------------+----------------
 Turning Point Scotland             | Drug Addiction
 Govan Youth Access Project         | Drug Addiction
 Community Learning West Team       | Drug Addiction
 Possil Learning Centre             | Drug Addiction
 Langside College (Glenwood Campus) | Drug Addiction
 Rehab Remanufacturing Services Ltd | Drug Addiction
 Greater Pollok Addiction Service   | Drug Addiction

db=# select orgname,usertype from users where usertype='Alcohol
Addiction';
              orgname               |     usertype
------------------------------------+-------------------
 Possil Learning Centre             | Alcohol Addiction
 Greater Pollok Age Concern         | Alcohol Addiction
 Rehab Remanufacturing Services Ltd | Alcohol Addiction
 Greater Pollok Addiction Service   | Alcohol Addiction



db=# select orgname from users where usertype='Alcohol
Addiction' and usertype ='Drug Addiction';
 orgname | usertype
---------+----------
(0 rows)

I would expect orgnames:
 Greater Pollok Addiction Service,
Rehab Remanufacturing Services Ltd
to be returned.
Any idea where I'm going wrong?

Cheers

Paul Butler