The best way is to be light-hearted and sorta halfway joking. Say "Dude, what is UP with your mood lately?" or jokingly ask her "Did you dog die or something?"

I would ask straight up, staring with "We love how/when you do/act like ___(something she does that's cool_. We haven't seen you doing that as much lately. Is something up? Have you felt a change?" .....something like that. It's specific, to the point, non-threatening, compassionate. She may even answer I hope so.

Once again, I completly disagree with Luisa (surprise, surprise). Saying something like that will totally trivialize someone's emotions and will NOT make them want to talk about it. Please don't do what she has suggested. To me, your friend sounds like she is suffering from depression. I would tell her that you have noticed she seems really down a lot and other people have as well. I would just tell her that you are feeling concerned about her because she is not acting like herself. Then just listen, she might have a lot to say and be greatful for the opportunity to have someone listen who cares. She may need to go see a counsellor or go on antidepressants. Don't be confrontational, approach her in a way which shows that you are concerned, she can't get mad at that. Good luck.

I totally agree with Janine22. Your friend needs your help, not your blame. If you're more concerned about your Friday nights getting ruined than your friend's potentially dangerous mental state, then you're not really a friend.

I agree with sunshowers. You are more concerned about what the other people around you think about her, than you are with what the root of the problem is. How hard is it to ask someone who's supposed to be your best friend, "Hey, you seem to be a little depressed lately. Anything you need to talk to someone about?" If you were truly her best friend, or a good friend at all, you certainly wouldn't need to come to a public form to figure out how to ask yuor BF what's wrong. Don't blame her for ruining your Friday nights. If it concerns you that much, just stop asking her to go out with you.

Do you ever meet your friend when you don't go out? Or is this more of a friendship that builds around going out and having fun? Do you talk about your life and serious issues? It might be that you don't know that much about your friend and there is a reason for her being down and you are just not aware of it. A lot of people also keep their worries to them selfs.
I would ask her, but not jokingly and also not when there are other people around so you can really talk. Tell her that you have noticed her being down and if there is anything you can do or if she would like to talk about it with you.
But if she really isn't that good of a friend and just a buddy you go out with and now that she is not a lot of fun anymore, be honest with yourself. Do you want to be a friend to her, even if that means it is not all fun and games, or are you not really that good friends and now that she is no more fun you prefer not to hang out?

I'll third Janine22's suggestions. Being depressive myself, I know how easy it is to slide into an even lower depression and not really realize it. What I've most appreciated is when friends or loved ones who *have* noticed the change come to me when no one else is around, and let me know that they've noticed I've been down a bit lately and ask what they could do to help me.

If she seems unsure what is wrong or what to do about it, maybe suggest that it might be helpful for her to find someone who's got experience helping people who aren't sure why they feel bad or what to do about it to help her figure out what she can do to get over this little bump. It's not as direct as just suggesting she see a shrink, but the goal is to put it to her in a way that doesn't sound judgmental or like you think she's "crazy," and indicates that you see her as someone who can help herself, but maybe just needs a bit of a nudge in the right direction. And if she needs something more than just a few sessions, she'll be in a place where the therapist can bring that up, while you provide her with moral support.

Whatever you do, I hope your friend gets to feeling better soon!

Listen to Janie22. It sounds like your friend is depressed and she needs your total support and understanding. I would suggest seeing a therapist. If she wants to consider antidepressants I can tell you as a sufferer of anxiety and depression that they do not work for everybody.

To another depressed person I would suggest: Talking to your friends (you), eating healthy, being active - interests / physical activities, staying away from drugs and drink (at least not binging) and last but not least: Talk to a specialist. The sooner she acts the better.

I also have a "feel good" mix every morning: Saint Johns Wort, Omega 3 and all the B vitamins.

Remember to be as supportive as possible and she will thank you when she gets better. If you feel lost and don't know how to "deal with" her, there is lots of information online as well as support groups for friends and relatives of people with mental health problems.

I agree with most of the other posters. It sounds like your friend is suffering from depression. Instead of worrying about what other people think and getting annoyed with her, you should let her know that you're there for her. That's what best friends do.

I went through a very dark time in my life 2 yrs ago. I was seriously battling depression and I have to say I lost some friends during this period. They found it more important to plan their nights out than trying to be supportive of what I was going through.

If I was down they just made the situation worse by thinking it was something they had done since when they would try and cheer me up and it just made me feel worse. It seemed like it was always about them. She could seriously be going through a very dark time and assuming it's just her being a "debbie downer" is tad insensitive.

It could be a lot more serious than you think.

SO happy to see posters give great advice on depression and being a good friend. It is great that you and her sister actually noticed her depression because most people tend to be too self-involved to give others a second thought. Unfortunately, you DO seem more concerned with how she comes off to outsiders than actually worrying about her mental state. Please put aside yourself for two seconds and ask your friend what you can do and explain that you are worried about her. It's the least you can do for your BEST FRIEND.

I agree with the commenters above - sounds like depression.

My mother once casually left a few pages that she had printed from a website on the coffee table, of course the intent was for me to find them. The pages discussed signs of depression, symptoms, treatments, etc. I don't think I was depressed - just going through "the whole world is against me" teenage years, but it did get her message across in a subtle, non-confrontational way.

Perhaps you or the girl's sister could find a book about depression, and 'accidentally' leave it out in a place where you know she will see it.

Don't "jokingly ask" if her dog died... what kind of question is that??

If it IS depression, try to approach the subject with care... make sure she knows you are concerned and want to be there for support.

I hate downers.

I had to get rid of all of the ones in my life. It was kind of sad but for the best.

I think the 20s are so filled with stress and uncertainty that its extra important to stay positive for your own mental health.

At first I dropped hints to my downer friends, then I stopped hanging out with them and was just vague and busy whenever they called, and then finally I just had to tell them that I needed to surround myself with positive people for my own sake.

It didnt really go over well, but at least I was free of the negativity and it has had such a profound effect on me that I hardly ever fall into my negative ways anymore like I used to when I was encouraged by the downers!

I would just politely bring up the situation. She could be depressed and might need someone to just make a gesture.

If it was my best friend, I would ask her gently about it (in private). I would be open to a heart-to-heart talk.

since its a best friend and not just an acquaintance bringing down the mood, you should talk to her privately.. and dont make it a joke like the first comment says thats just rude and will make things worse.

I'd talk to her about it and forcer her to tell her what to day. It could just be because it's winter and she feels couped up and is irritable. It could also be a case of depression that she should get some help with.

Forcing her to talk wouldn't be appropriate - she may need some time to think about what she feels comfortable saying or who she's most comfortable saying it to. This is one area where being confrontational could be disastrous, because if she actually *is* depressed and gets put on the defensive, it can actually make her depression worse. It may take her a bit to accept the idea that she could be depressive and realize she needs help - if that is, indeed, the case. You need to approach her gently and sort of follow her lead, with maybe a GENTLE nudge now and again if she seems to stay stuck in this low-mood mode.

I couldn't let this one go. I work in a hospital ER and suicidal people, suicide attempters and those who've died come in ALL THE TIME.
I want to echo the suggestions of others - take another friend with you, meet your friend for coffee and ask her if she's depressed and even ask her if she has thought about hurting herself. Offer to help her get help. Encourage her to get help. Do what you can.
I know it's hard to understand if you've never been through more than a few hours or even a few days of feeling down, but think, if she did commit suicide, what would you be saying "I'm so sorry I didn't try to help." OR "Wow, but she was such a downer."???