Drinking alcohol can be harmful when combined with certain cancer treatments and antidepressant medications, so you will need to check with your GP or specialist. If it is safe for you to drink, continuing to socialise can be a positive thing when you are going through cancer treatment, a welcome distraction, and a way of not feeling different from everyone else.
However, remember that too much alcohol can actually cause problems. It can be damaging to relationships, reduce the quality of your sleep making you feel more tired, and have a depressant effect making you feel even more low. So keep alcohol to a minimum.
Recreational drugs can make you feel better short-term, but long-term they may be very damaging to your health, and should be avoided altogether.