How do YOU cure sadness?

Wait for it to pass. Of course, you can also expose yourself to comedic stimuli.

I agree with @Blackberry that it take time. Meanwhile, religion if you’re so inclined, music, hard walking or other strenuous exercise (to get the anger out). For a quick temporary fix: a good movie, preferably a comedy and a hot fudge sundae. What can friends do? Be there. Cook a meal or two. Take walks together and let your friend talk or not talk. Do things together.

Is someone else sad? There is not much you can do except tell them you are there for them. The mean it: contact them.

If you are sad, there is nothing much to be done but get through it. Experience your feeling s fully. Time will lessen the pain.

Time heals most, and what it can’t heal at least starts to feel less painful… distractions that make you happy (and not think about the sad stuff) is the only place to start

A huge hug.

Wait until it passes.
Find something else to think about.
Exercise.

Do something else to not think about it, until I believe I’m clear and calm enough to be able to start dealing with it. I guess it really depends on what it is, but if you need to deal with it, personally I find that shoving it in the background for a bit helps to better deal with it later on. Do something you like, such as a hobby, read or watch something you love.

I usually just wallow in it for a while and fall asleep, I’ve found even a short nap to help out with bouts of sadness. Interesting how sometimes small children cry because they are tired, but we rarely make the connection when we’re adults ;-)

Can’t cure it or get rid of it completely, you just find a way to work around it and handle life with it.

A temporary distraction is good if the sadness is overwhelming you. At some point, though, you just have to feel the sadness fully, and allow time to do its work. I’m sorry you and your friend are sad, and I hope it passes soon.

Never stifle it, you’re fighting a losing battle there.
Face it full on, process it in a healthy/practical way that can only lead to ultimate closure & positivity.
In other words, don’t let the bastards grind you down.

By applying Martin Seligman’s PERMA model. Google it in case you’re interested. The recommendations are based on sound scientific studies.