I recently went from taking 20 mg celexa (citalopram) to 40 mg celexa (citalopram), about 4 days ago. When will I start to feel better?

2-3 weeks minimum. for all SSRIs like citalopram, 2-3 weeks for a partial effect, 4-6 weeks for a full effect.
Patience. it can take up to 4 weeks to see a response as we're waiting for new protein synthesis in brain neurons.
Weeks. It can happen faster, but an increase in an SSRI like citalopram typically requires 2 to 3 weeks to develop an noticeable result.
It can take. days to weeks, and the changes are usually subtle. Often it's other people who notice changes before you do, such as you're smiling a little easier than usual, or you do a little more than you were. Ask the people around you to let you know what they notice over the next few weeks, if you feel comfortable with that; it may help you to keep track of how you're actually doing. Good luck!
Depression, Celexa (citalopram) Celexa (citalopram) is a medication for Depression. It is likely that the dose was increased due to your continued depression and lack of response with Celexa (citalopram) 20mg/day. Improvement in Depression will happen from adding psychotherapy, improving self-esteem, Breathing Relaxation, Visual imagery, Tai Chi, Yoga, Meditation and exercise. See a Psychiatrist for Therapy for stressors and monitoring of medication.
It depends. on your unique sensitivity, other medications affects on the antidepressant, other associated medical illnesses, comorbid psychiatric illnesses , liver enzyme profile, side effects of the antidepressant itself, and whether the dose is adequate to provide remission. It can occur very early, as soon as several days, to six weeks. Gradual improvement is more typical rather than snapping out of it.
Days to weeks. I may take some where from a few days but rather weeks to feel a difference.
Two weeks. I explain to my patients on antidepressants that it usually takes about two weeks for noticeable effects to begin to kick in, about four weeks to have the majority of the benefits show up.
Couple of weeks. It can take a couple of weeks or more to have the full effects of this medication. Some people will detect some changes sooner.
4-6 weeks. could take up to 4-6 weeks to experience the full benefit of the med change. (although unsure as to the symptoms you are referring to). May likely notice some benefit sooner. Difficult to say for sure. best to work on other non-med options (exercise, therapy, engaging activities, etc) to help in the mean time and not rely on the medication alone to help with symptom relief.
On average 4 weeks. On average it takes 4-5 weeks for maximal effect of Celexa, (citalopram) either when starting the medication or increasing the dose. However, this is when it's used for treating depression. It may be less effective for treating anxiety and, taken by itself, may actually aggravate the symptoms of bipolar illness. Please stay in touch with doctor who's treating you!