Short answer: not in the form most people mean by it, and there is decent evidence that the straightforward version can make some people feel worse.
That is not a comfortable thing to say in the wellness field, where positive thinking is close to a house religion. But something more useful survives once you take the wishful part out, and it is worth being precise about what that is.
The basic question
Does positive thinking work?
Deciding to think positive thoughts, on its own, is a weak intervention, and for people who are already struggling it can backfire.
The problem is mechanical rather than moral. A thought like "everything is going to be fine" has to get past a mind that has evidence to the contrary. When it does not get past, you have not changed your mood. You have added a second unpleasant experience on top of the first: the original worry, plus the fresh information that you cannot even think correctly about it.
What does work is a set of narrower, less inspiring practices. Changing what you attend to. Examining whether the story you are telling yourself is actually accurate. Doing one small thing. None of these require you to feel positive first, which is exactly why they work when you do not.
Why do positive affirmations sometimes make people feel worse?
Because a statement you do not believe invites your mind to argue with it, and your mind wins.
Say "I am confident and capable" to yourself when you do not feel it, and notice what actually happens next. Most people report an immediate internal rebuttal, and the rebuttal arrives with supporting evidence. You have effectively prompted yourself to list your failures.
Research on positive self-statements has found this effect is not evenly distributed: people who already feel good about themselves get a mild lift, while people with low self-esteem, the group the advice is usually aimed at, tend to feel worse afterward (Wood, Perunovic, and Lee, 2009, Psychological Science, https://doi.org/10.1111/j.1467-9280.2009.02370.x).
This is the central irony of the genre. The advice works best for the people who need it least.
Isn't this just toxic positivity?
Toxic positivity is not positive thinking done badly. It is positive thinking pointed at someone else.
Applied to yourself, insisting on the bright side is mostly ineffective. Applied to another person who is struggling, it does real damage, because "at least" and "everything happens for a reason" tell them their experience is unwelcome. The most common result is not comfort. It is that they stop telling you things.
Patty put this well in her article on what reframing is, and what it is not. The bright side, she notes, is usually offered by people who are not currently standing in the dark.
What to do instead
What is the difference between optimism and positive thinking?
Positive thinking asserts that the outcome will be good. Optimism expects that you will be able to handle whatever outcome arrives. Only the second one survives contact with a bad week.
The distinction matters because the two feel similar from the inside and behave completely differently under pressure. Positive thinking is a claim about the world, and the world can contradict it. Optimism is a claim about your own capacity to cope and adapt, and it is much harder to disprove, because most of the time it is true. You have handled everything so far.
If you want one thing to move, move that. Not "this will be fine" but "whatever this turns out to be, I will deal with it."
What actually works, if not positive thinking?
Three things, in rough order of how reliably they work:
Accuracy, rather than positivity. Ask whether the story you are carrying is the most accurate one available, not the nicest one. Often it is not accurate, and correcting it downward toward the truth feels better than inflating it upward toward the pleasant. This is cognitive reappraisal, and it is among the better studied ways of regulating emotion. Patty's piece on reframing walks through the method properly.
Attention, rather than content. You have very little control over which thoughts arrive. You have considerably more over which ones you stay with. This is the entire premise of meditation practice and it is a genuinely different skill from thinking better thoughts.
Action, rather than either. Doing one small concrete thing changes your emotional state faster than any amount of internal argument. Answer the email you have been dreading. Take the walk. Motivation is more often a result of action than a prerequisite for it.
Does gratitude actually change anything?
Gratitude is the most robust member of this family, with a real caveat: it works when it is specific and honest, and does very little when it is a list.
"I am grateful for my health, my family, my job" is a category list, and your mind processes it as one. "I am grateful that my neighbor took the bins out on Tuesday without mentioning it" is an actual memory, and it arrives with the feeling attached.
The effect sizes in gratitude research are consistently positive but moderate. It is not a cure for anything. It is a small reliable adjustment to what your attention notices by default, which over months is not nothing.
How long before I notice a difference?
For attention practices, most people notice something within two to three weeks of near-daily practice. Not serenity. Something smaller and more useful: a half-second gap between an event and your reaction to it, which was not there before.
That gap is the whole thing. Everything else is built on it.
Where meditation fits
People often assume meditation is positive thinking with better posture. It is close to the opposite.
Nothing in the practice asks you to think pleasant thoughts, or any thoughts at all. What you are training is the capacity to notice what your mind is doing while it is doing it, and to choose whether to follow. Some sessions are lovely. Plenty are boring or uncomfortable, and those count exactly the same, because you are not practicing feeling good. You are practicing noticing.
That is why it holds up on the days positive thinking collapses. You do not need to believe anything in particular in order to notice what is happening.
If you want somewhere concrete to start, three simple breathing practices for a busy workday will take you about five minutes. The companion piece to this one, on why you cannot stop thinking, deals with the objection almost everyone raises first.
One honest caveat
Everything here is about ordinary difficulty: a bad week, a hard conversation, work that has become heavy.
Some things are not in that category, and no amount of attention training or accurate reframing is the right tool for them. If what you are carrying is persistent, or getting heavier rather than lighter, that is worth talking to a professional about. That is not a failure of practice. It is knowing which tool the situation calls for, which is itself a form of clear thinking.