Citalopram at 20 mg is the standard starting dose for treating depression in adults, and for some people it’s also the maintenance dose they stay on long-term. It works by increasing the amount of serotonin available in your brain, which gradually improves mood, energy, and emotional stability over the course of several weeks. For adults over 60 or those with liver problems, 20 mg is actually the maximum recommended dose.
How It Works in Your Brain
Citalopram belongs to a class of antidepressants called SSRIs, or selective serotonin reuptake inhibitors. Serotonin is a chemical messenger that carries signals between nerve cells. Normally, after serotonin delivers its signal, it gets pulled back into the cell that released it. Citalopram blocks that recycling process, leaving more serotonin circulating between nerve cells. The word “selective” matters here: unlike older antidepressants that affected multiple brain chemicals at once, citalopram primarily targets serotonin, which is one reason it tends to cause fewer side effects than earlier medications.
Once you swallow a 20 mg tablet, your liver processes it with a half-life of about 35 hours, meaning it takes roughly a day and a half for your body to clear half the dose. With daily dosing, the drug reaches a stable level in your bloodstream within about one week. That steady level is what allows it to consistently influence serotonin signaling.
What You Can Expect to Feel, and When
The timeline catches many people off guard. You may notice some initial changes within one to two weeks, often in physical symptoms like sleep quality or energy levels. But the full antidepressant effect typically takes four to six weeks of daily dosing. For anxiety-related conditions (generalized anxiety, social anxiety, panic disorder), a similar pattern applies: early improvements within two weeks, with continued gains through week four to six.
This delay doesn’t mean the medication isn’t working. Your brain needs time to adapt to the new serotonin levels and make downstream adjustments in how nerve cells communicate. The lag is a normal part of the process, not a sign that the dose is wrong.
Common Side Effects at This Dose
Most side effects are mild and tend to appear in the first week or two, often fading as your body adjusts. In clinical trials, the most frequently reported issues were:
- Nausea (21% of patients, compared to 14% on placebo)
- Dry mouth (20% vs. 14%)
- Drowsiness (18% vs. 10%)
- Insomnia (15% vs. 14%)
- Increased sweating (11% vs. 9%)
- Diarrhea (8% vs. 5%)
- Tremor (8% vs. 6%)
Sexual side effects are common enough to be worth knowing about. Among men in clinical trials, about 6% experienced delayed ejaculation, nearly 4% reported decreased sex drive, and about 3% reported erectile difficulties. For women, decreased sex drive and difficulty reaching orgasm were reported at lower rates (around 1% each), though sexual side effects in women are widely thought to be underreported.
Several of these side effects are dose-dependent, meaning they become more likely at higher doses. Fatigue, insomnia, drowsiness, increased sweating, and yawning all showed a clear pattern of increasing with dose in clinical studies. This is one reason many doctors start at 20 mg and only increase if needed.
Why 20 mg Is the Maximum for Some People
For most adults under 60, the dose can range from 20 to 40 mg. But 20 mg is the hard ceiling for several groups: adults over 60, people with liver impairment, and people whose genetics make them slow metabolizers of the drug (specifically, those with reduced activity of a liver enzyme called CYP2C19). All of these factors cause the drug to build up to higher-than-normal levels in the bloodstream.
The concern is a heart rhythm issue called QT prolongation, where the electrical cycle of the heartbeat takes slightly longer than it should. At 20 mg per day, citalopram extends this interval by an average of 7.5 milliseconds, a small and generally safe change. At 60 mg, that number jumps to 16.7 milliseconds, which starts to carry meaningful risk. For people who already clear the drug more slowly, even a standard dose produces higher blood levels, so the lower cap protects against this cardiac effect.
People with preexisting heart rhythm disorders, very slow heart rates, or recent heart failure need extra caution. Citalopram also shouldn’t be combined with other medications that affect heart rhythm, since the effects can stack.
What Happens If You Stop Taking It
Stopping citalopram abruptly, even at 20 mg, can trigger discontinuation symptoms within a day or two. These may include dizziness, nausea, headaches, irritability, insomnia, vivid dreams, flu-like aches, and a distinctive sensation often described as “brain zaps,” brief electric-shock-like feelings in the head. Depression symptoms can also rebound.
These withdrawal effects aren’t dangerous, but they can be uncomfortable enough to disrupt your daily life. The standard approach is to taper gradually over several weeks, reducing the dose in steps so your brain can readjust to lower serotonin levels. The longer you’ve been taking citalopram, the more gradual the taper typically needs to be.
Factors That Affect How Well It Works for You
Your genetics play a real role. People who are “ultrarapid metabolizers” of CYP2C19 break down citalopram faster than normal, which can mean the drug doesn’t reach effective levels. People who are “poor metabolizers” break it down slowly, leading to higher blood levels and more side effects at the same dose. Pharmacogenetic testing can identify which category you fall into, and clinical guidelines recommend that poor and ultrarapid metabolizers consider an antidepressant that uses a different metabolic pathway.
Other medications matter too. Drugs that inhibit CYP2C19, including some common stomach acid reducers, can raise citalopram levels in your blood. Kidney function, liver function, and age all influence how your body handles the medication. These aren’t reasons to avoid citalopram, but they’re reasons your prescriber may choose 20 mg as both the starting and final dose rather than increasing it.