This was true a hundred years ago.
The Catholic Church has mellowed on this subject over the centuries as knowledge of mental illness and depression has increased.
Catholics believe suicide when committed in full knowledge and deliberate consent is a complete turning away from God (a mortal sin) and will send a person to hell.
There are 3 conditions of a mortal sin: grave matter, full knowledge, and deliberate consent.
While suicide (or any kind of murder) is always a grave matter, people who commit suicide may not always have full knowledge of what they're doing. Drugs can definitely impair one's thinking, as can other things, such as diseases, intense pain, or anguish.
Therefore, suicide is not automatically treated as a mortal sin.
We are commanded by Christ not to judge others so we leave final judgment to God who alone knows each person's heart.
The Code of Canon Law does not list suicide as a reason to deny a person a Catholic funeral or burial in a Catholic cemetery. http://www.vatican.va/archive/ENG1104/__P4C.HTM
http://www.holycrosscemeteries.com/faq/#Section_17
http://home.att.net/~faithleap/suicide.htm
For more information, see the Catechism of the Catholic Church:
On mortal sin, paragraphs 1857-1859: http://www.usccb.org/catechism/text/pt3sect1chpt1art8.htm#1857
On suicide, paragraphs 2282-2283: http://www.usccb.org/catechism/text/pt3sect2chpt2art5.htm#2282
With love and prayers in Christ.